JP2018134023A - Low-acid fermented milk production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fermented milk production method in which fermentation rate of fermented milk is maintained in a first half period of fermentation, and reduction of pH is effectively suppressed in a latter half period of fermentation.SOLUTION: The fermented milk production method in a first embodiment includes: a primary fermentation step of performing, in a fermentation-promoting temperature range, primary fermentation on a fermented milk base material in which a lactobacillus starter is added to a raw material mix; a heat treatment step of holding fermented milk base material after being subjected to the primary fermentation step for a predetermined period of time in a middle and high temperature range of 53 to 63°C which is temperature higher than the fermentation-promoting temperature range; and a secondary fermentation step of performing secondary fermentation on the fermented milk base material after the heat treatment step in the fermentation-promoting temperature range. The fermented milk production method in a second embodiment is also provided that is identical to the fermented milk production method in the first embodiment except that: heat treatment step is started at a stage where pH of the fermented milk base material reaches 6 to 4 in the primary fermentation step; time for holding the fermented milk base material in the middle and high temperature range in the heat treatment step is 2 to 30 minutes; time required until pH of the fermented milk base material reaches from 4.6 to 4.4 in the secondary fermentation step is 1.9 house or more; and time required until pH of the fermented milk base material reaches 4.6 in the primary fermentation step is 30 hours or less.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for producing fermented milk. If it demonstrates concretely, this invention relates to the manufacturing method of fermented milk which suppressed the raise of the acidity during fermentation.

  Fermented milk is milk or milk containing non-fat milk solids equal to or higher than milk or lactic acid bacteria or yeast in Japan's “Ministerial Ordinance on Component Standards for Milk and Dairy Products” (hereinafter referred to as “Milk Ordinance”). It is defined as a fermented paste-like or liquid form or a frozen form thereof. Examples of fermented milk are set-type yogurt (solid fermented milk), soft-type yogurt (paste-like fermented milk), and drink-type yogurt (liquid fermented milk). Set-type yogurt is obtained mainly by fermenting a raw material mix after filling into a container and solidifying it in the container. Soft yogurt can be obtained by fermenting the raw material mix, crushing the curd in a large tank, etc., mixing with pulp or sauce as necessary, and then filling the container. The drink yogurt can be obtained by finely crushing the above set type or soft yogurt with a homogenizer or the like, mixing it with pulp or sauce as necessary, and filling it into a container.

In addition, fermented milk must have a non-fat milk solid content of 8.0% or more and a total number of lactic acid bacteria of 1.0 × 10 ⁷ cfu / g or more in accordance with the ingredient standards of the Japanese milk ministerial ordinance. It has been established. Furthermore, the international standard for yogurt by FAO / WHO also stipulates that a large amount of microorganisms (Bulgaria, Thermophilus) must survive in the final product.

  Thus, fermented milk contains a large amount of live bacteria such as lactic acid bacteria. Therefore, when fermented milk (or a fermented milk base material used as a raw material thereof) is stored for a long period of time, the pH is lowered by lactic acid produced by lactic acid bacteria and the sourness becomes strong. In this way, when fermented milk is stored for a long period of time, the pH will decrease with time compared to that immediately after production, and it is therefore difficult to maintain the flavor and quality of fermented milk for a long period of time. It was.

  Various methods have been proposed in the past to solve the above-described problem of pH reduction of fermented milk. As means for suppressing the sourness increase of fermented milk, for example, a method of adding peroxidase (Patent Document 1), a method of using low-temperature sensitive lactic acid bacteria (Patent Document 2), and a method of aging in an ice temperate zone after the end of fermentation (Patent Document 3) is known.

JP-A-10-262550 JP 2000-270844 A JP 2003-259802 A

  However, in the conventional methods disclosed in the above-mentioned patent documents, new additives such as peroxidase are further added, applicable lactic acid bacteria are limited, or a new cooling process such as ice temperate ripening is introduced. As a result, there are problems such as complicated manufacturing.

  Also, in the case of mass production of fermented milk industrially, considering its production efficiency, the fermentation rate of the raw material mix is increased (fermentation time is shortened) in the first half of fermentation from pH 6.6 to pH 4.6. It is desirable to do. However, if the fermentation rate is increased, lactic acid and the like are produced at an early stage. Therefore, when fermented milk is stored for a long period of time, there is a problem that the pH is lowered in the latter half of the fermentation and the sourness becomes stronger. . In response to this problem, no technology has yet been proposed that can maintain the fermentation rate in the first half of the fermentation at a rate suitable for mass production of fermented milk, while effectively suppressing the decrease in pH in the second half of the fermentation. .

  In particular, concentrated fermented milk such as Greek yogurt requires several hours for the concentration process in which the fermented milk is allowed to stand and separate into light liquid (whey) and heavy liquid (concentrated fermented milk). As fermentation progresses, there is a problem that the sourness of the product finally obtained becomes stronger. As a countermeasure for such a problem, in the concentration step, fermentation can be suppressed by lowering the temperature of the fermented milk before concentration, but the separation efficiency of light liquid and heavy liquid is extremely reduced. As another measure, there is a method of using a lactic acid bacteria starter with low acid generation ability, but the difference in pH between concentrated fermented milk at the start of concentration and immediately before the end of concentration increases, and the quality of the final product, especially the degree of acidity There is a problem that it is not suitable for industrial production of concentrated fermented milk. For this reason, when considering the industrial production of concentrated fermented milk, use a lactic acid bacteria starter with a certain acid-producing ability such as Bulgarian bacteria and Thermophilus bacteria, and maintain the temperature of the fermented milk at around 40 ° C in the concentration process. It is desirable. However, under such conditions, fermentation of the fermented milk proceeds in the concentration step, and the sourness of the final product (concentrated fermented milk) becomes strong. Thus, it is said that it is difficult to suppress the sourness and fermentation odor of concentrated fermented milk.

  Therefore, the present invention basically provides a method for producing fermented milk that can effectively maintain the fermentation rate of the fermented milk during the first half of the fermentation and can effectively suppress the decrease in pH during the second half of the fermentation. For the purpose. Furthermore, the present invention uses, for example, a lactic acid bacteria starter having a certain acid-producing ability such as Bulgaria bacteria and Thermophilus bacteria in producing concentrated fermented milk, and maintains the temperature of the fermented milk at around 40 ° C. in the concentration process. Even if it is a case, it aims at obtaining the concentrated fermented milk by which the fall of pH was suppressed in the concentration process and the acidity and fermentation odor were suppressed.

  The inventors of the present invention have intensively studied the means for solving the problems of the conventional invention, and as a result, the fermented milk base material is firstly fermented in the fermentation promotion temperature range, and then the temperature is higher than that in the fermentation process. Lowering the pH in the second half of the fermentation while maintaining the fermentation rate in the first half of the fermentation by performing a heat treatment that is maintained for a certain period of time at a medium to high temperature range of 53 to 63 ° C. The knowledge that it can suppress effectively is acquired. Furthermore, it has been found that if such fermentation technology is developed, concentrated fermented milk with reduced acidity and fermentation odor can be efficiently produced, for example, by suppressing a decrease in pH in the concentration step. The inventors of the present invention have come up with the idea that the problems of the prior art can be solved based on the above knowledge, and have completed the present invention. Hereinafter, the method for producing fermented milk according to the present invention will be specifically described.

  The present invention relates to a method for producing fermented milk. The production method of the present invention includes a primary fermentation process, a heat treatment process, and a secondary fermentation process. The primary fermentation process is a process in which a fermented milk base material in which a lactic acid bacteria starter is added to a raw material mix is subjected to primary fermentation in a fermentation promotion temperature range. The heat treatment step is a step of holding the fermented milk base material after the primary fermentation step in a medium to high temperature range of 53 to 63 ° C. that is higher than the fermentation promotion temperature range for a certain period of time. The secondary fermentation step is a step of subjecting the fermented milk base material after the heat treatment step to secondary fermentation in a fermentation promotion temperature range. In addition, the temperature which carries out the secondary fermentation of the fermented milk base material should just be in a fermentation promotion temperature range, and may differ from the temperature which carries out primary fermentation of a fermented milk base material.

  Reduce fermentation rate in the first half of fermentation by holding the fermented milk base material during fermentation for a certain period of time in the middle and high temperature range that is above the fermentation acceleration temperature and does not kill the lactic acid bacteria starter as in the above process However, it succeeded in slowing the fermentation rate in the second half of the fermentation and suppressing acid production. Thereby, it is possible to efficiently produce a savory fermented milk in which acidity and fermentation odor are suppressed. Further, according to the present invention, the acidity during long-term storage can be controlled with respect to the problem that it is difficult to keep the quality of fermented milk constant for a long time. Furthermore, since the sourness and fermentation odor can be reduced, other flavor substances added to fermented milk and adjunct starters (starters that do not affect card formation but have a role such as flavor addition) can be added. Can be maintained.

  In the present invention, in the heat treatment step, the pH (acidity) of the fermented milk base material in the primary fermentation step is preferably 6 to 4, more preferably 5.8 to 4.1, and still more preferably 5.5 to 4. 2. It is particularly preferable to start at the stage when the value becomes 5.2 to 4.3. That is, the heat treatment step is executed in a period immediately before fermentation of the fermented milk base material proceeds to some extent and reaches the target pH. In this way, by strictly controlling the start time of the heat treatment step, it is possible to effectively suppress a decrease in pH in the second half of the fermentation while maintaining the fermentation rate in the first half of the fermentation. That is, when the heat treatment step is performed before the pH of the fermented milk base material reaches 5.2, the pH of the fermented milk base material is delayed until reaching the target value, and thus the production efficiency is lowered. On the other hand, when the heat treatment step is performed after the pH of the fermented milk base is less than 4.3, the pH of the fermented milk is excessively lowered, and the acidity and fermentation odor cannot be suppressed. Therefore, in the present invention, the pH of the fermented milk base material is accurately measured, preferably 6 to 4, more preferably 5.8 to 4.1, still more preferably 5.5 to 4.2, particularly preferably pH 5. It is better to start the heat treatment step in the range of 2 to 4.3.

  In this invention, it is preferable that the time which hold | maintains a fermented milk base material in a middle-high temperature range in a heat processing process is 2 to 30 minutes. If the holding time in the medium and high temperature range is less than 2 minutes, the effect of the heat treatment step cannot be exhibited, but if it exceeds 30 minutes, the lactic acid bacteria starter in the fermented milk base material may be killed. Therefore, it is preferable to control the holding time in the medium to high temperature range to 2 to 30 minutes.

  In the present invention, the fermentation promotion temperature range is 30 to 50 ° C. In this case, after the primary fermentation process, the fermented milk base material in the fermentation promotion temperature range is continuously heated to the medium-high temperature range without cooling the fermented milk base material, and the heat treatment in this medium-high temperature range is performed. It is preferable to carry out. When the fermented milk base in the 30-50 ° C fermentation promotion temperature range is once cooled and then heated to a medium-high temperature range of 53-63 ° C, the temperature difference becomes too large, and the lactic acid bacteria in the fermented milk base There are concerns that many starters will die or their vitality will decline significantly. If it does so, there exists a problem that fermentation of a fermented milk base material will not be performed moderately in a secondary fermentation process. In addition, if time and energy are consumed in the cooling process before the heat treatment process, the production efficiency is lowered, and therefore it is not suitable for industrial production of fermented milk. Therefore, as described above, the primary fermentation step and the heat treatment step are preferably performed continuously without passing through the cooling step. Conventionally, it has been considered that such a heating treatment is not preferable because further heating of the fermented milk base material during the fermentation process leads to deterioration of the yogurt tissue. By performing the heat treatment under heating conditions (temperature and time), there was no problem in the flavor of the fermented milk finally obtained.

  In the present invention, the time required for the pH of the fermented milk base material to change from 4.6 to 4.4 is preferably 1.9 hours or more. In particular, the required time is preferably 4 hours or more. As an example, in the secondary fermentation process, the fermented milk base material may be allowed to stand at 43 ° C. When the fermented milk base is fermented without passing through the heat treatment step, the time required for the pH to change from 4.6 to 4.4 is generally about 1 hour. On the other hand, according to the present invention, this required time can be doubled or more by performing the heat treatment step. Therefore, in the secondary fermentation process, the fermented milk base material was allowed to stand at around 40 ° C. (about ± 3 ° C.), and a concentration process was performed to separate light liquid (whey) and heavy liquid (concentrated fermented milk). Even if it is a case, the acidity and fermentation odor of the obtained concentrated fermented milk can be suppressed. For this reason, according to this invention, the concentrated fermented milk represented by Greek yogurt can be manufactured efficiently.

  In the present invention, the time required from the start of the primary fermentation process until the pH of the fermented milk base becomes 4.6 is preferably 30 hours or less, more preferably 8 hours or less, and 4 hours. It is particularly preferred that In addition, the time of the start of a primary fermentation process is the time of completing inoculation of the lactic acid bacteria starter to a raw material mix. Thus, it can avoid that the manufacturing efficiency of fermented milk falls by making time to reach pH 4.6 from the time of the start of a primary fermentation process (at the time of completion of lactic acid bacteria starter inoculation) to 8 hours or less. Moreover, when fermented milk base material is fermented without passing through the heat treatment process, the time required from the start of the fermentation process to reaching pH 4.6 is generally about 4 hours. Therefore, also in the present invention, by setting the required time to 4 hours or less, even when the heat treatment step is performed, the fermentation rate in the primary fermentation step (first half of fermentation) is set to the case where the heat treatment step is not performed. Can maintain the same speed.

  In the present invention, the lactic acid bacteria starter preferably contains Bulgaria bacteria and Thermophilus bacteria. Bulgarian bacteria and Thermophilus bacteria have a certain acid-producing ability. According to the present invention, even when such a lactic acid bacteria starter is used, acid production in the latter half of the fermentation is suppressed, and the resulting fermented milk is obtained. The sour taste and fermentation odor can be suppressed.

In the present invention, when the pH of the fermented milk base material reaches 4.6, the heat treatment step is started, and after that, when the secondary fermentation step is performed by cooling to 10 ° C., 7 hours from the start of the primary fermentation step. The pH of the fermented milk base material after the passage of days is preferably 4.2 or more. In this case, the total number of lactic acid bacteria in the fermented milk base material after 35 days from the start of the primary fermentation process is preferably 1.0 × 10 ⁷ cfu / g or more. Thus, according to the present invention, the pH of 4.2 or higher can be maintained even after storing the fermented milk for a long period of time, so it can be said that the acidity is suppressed. Moreover, even after 35 days, the total number of lactic acid bacteria (1.0 × 10 ⁷ cfu / g or more) determined by the Japanese ordinance of milk can be maintained.

  The production method of the present invention further includes a heat sterilization step for heat sterilizing the raw material mix, a primary cooling step for cooling the raw material mix after the heat sterilization step, and a lactic acid bacterium in the raw material mix during or after the primary cooling step. A starter addition step of adding a starter to obtain a fermented milk base material, a primary heating step for heating the fermented milk base material after the starter addition step to a fermentation promoting temperature range, and a fermented milk base material after the primary fermentation step It is preferable to further include a secondary heating step for heating to a medium-high temperature range and a secondary cooling step for cooling the fermented milk base material after the heat treatment step to a fermentation promotion temperature range.

  According to the present invention, it is possible to effectively suppress a decrease in pH in the second half of fermentation while maintaining the fermentation rate of the fermented milk in the first half of fermentation. Furthermore, according to the present invention, in producing concentrated fermented milk, a lactic acid bacteria starter having a certain acid-producing ability such as Bulgarian bacteria and Thermophilus bacteria is used, and the temperature of the fermented milk is maintained at around 40 ° C. in the concentration process. Even if it does, it can suppress the fall of pH in a concentration process, and can obtain the concentrated fermented milk by which the acidity and fermentation odor were suppressed.

FIG. 1 is a flowchart showing the manufacturing process of a manufacturing method according to an embodiment of the present invention. FIG. 2 schematically shows the transition (1) of the pH of the fermented milk base material when the heat treatment is performed according to the present invention and the transition (2) of the pH of the fermented milk base material when the heat treatment is not performed. It is a graph.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. This invention is not limited to the form demonstrated below, The thing suitably changed in the range obvious to those skilled in the art from the following forms is also included.

  In the present specification, the “raw material mix” means a liquid containing milk components such as raw milk, whole milk, skim milk, whey and the like before the starter addition step. Here, raw milk refers to animal milk such as milk. In addition to milk components such as raw milk, whole milk, skim milk and whey, the raw material mix includes processed products (for example, whole milk powder, whole fat concentrated milk, skim milk powder, condensed skim milk, condensed milk, whey powder, Including buttermilk, butter, cream, cheese, whey protein concentrate (WPC), whey protein isolate (WPI), α-lactalbumin (α-La), β-lactoglobulin (β-Lg), etc.) Can do. The “fermented milk base (yogurt base)” means a state after adding a lactic acid bacteria starter to a raw material mix. Moreover, "fermented milk" means a product obtained in a state after completion of the fermentation process, obtained by fermenting a fermented milk base material. In the present specification, “A to B” means “A or more and B or less”.

  The present invention relates to a method for producing fermented milk. An example of fermented milk is yogurt. The fermented milk may be a set-type yogurt, a soft-type yogurt, or a drink-type yogurt. It is also possible to use the fermented milk produced according to the present invention as a material for frozen yogurt. It is also possible to use the fermented milk produced according to the present invention as a cheese material. In the present invention, the fermented milk may be any of “fermented milk”, “dairy lactic acid bacteria beverage”, “lactic acid bacteria beverage” and the like defined by an ordinance of milk.

  FIG. 1 is a flowchart showing each step of a manufacturing method according to an embodiment of the present invention. As shown in FIG. 1, the method for producing fermented milk according to the present invention includes a raw material mix preparation step (step S1), a heat sterilization step (step S2), a primary cooling step (step S3), and a starter addition step (step S4). ), Primary heating step (step S5), primary fermentation step (step S6), secondary fermentation step (step S7), heat treatment step (step S8), secondary cooling step (step S9), secondary fermentation step (step) S10) and a tertiary cooling step (step S11) are preferably included.

  As shown in FIG. 1, a raw material mix preparation step (step S1) is first performed in producing fermented milk. A raw material mix preparation process is a process of preparing the raw material mix used as the material of fermented milk. The raw material mix is also called yogurt mix. In this invention, a well-known thing can be used for a raw material mix. For example, the raw material mix may consist only of raw milk (raw milk 100%). In addition to raw milk, whole fat milk, skimmed milk, whey and other milk components, the raw material mix includes processed products (for example, whole milk powder, whole fat concentrated milk, skim milk powder, skimmed concentrated milk, condensed milk, whey powder) , Buttermilk, butter, cream, cheese, whey protein concentrate (WPC), whey protein isolate (WPI), α-lactalbumin (α-La), β-lactoglobulin (β-Lg), etc.) It may be prepared as described above. In addition to milk components, the raw material mix includes soy milk, sugar, sugars, sweeteners, flavors, fruit juice, pulp, vitamins, minerals, fats and oils, ceramides, collagen, milk phospholipids, polyphenols, food ingredients and It can contain food additives and the like. In addition, the raw material mix may contain stabilizers such as pectin, soybean polysaccharide, CMC (carboxymethylcellulose), agar, gelatin, carrageenan, gums, thickener, gelling agent, and the like, if necessary. . In the raw material mix preparation step, it is preferable to finely sulfurize (pulverize) fat globules and the like contained in the raw material mix by a homogenization step of homogenizing the raw material mix. By this homogenization process, it is possible to suppress or prevent the raw material mix, the fermented milk base material, and the fat content of the fermented milk from separating or rising during the manufacturing process or after the manufacturing of the fermented milk.

  The heat sterilization step (step S2) is performed after the raw material mix preparation step. The sterilization process is a process of heating and sterilizing the raw material mix. For example, in the heat sterilization step, heat treatment may be performed by adjusting the heating temperature and the heating time to such an extent that germs in the raw material mix can be sterilized. In the present invention, a known method can be used for the heat sterilization step. For example, in the heat sterilization process, heat treatment may be performed with a plate heat exchanger, tube heat exchanger, steam injection heating device, steam infusion heating device, energizing heating device, etc. Heat treatment may be performed. In the heat sterilization process, when the yogurt is plain type, hard type or soft type, heat treatment such as high temperature short time sterilization (HTST) may be performed. Heat treatment such as sterilization treatment (UHT) may be performed. Furthermore, for example, in the heat sterilization process, the high temperature short time sterilization process (HTST) may be a process in which the raw material mix is heated to 80 ° C. to 100 ° C. for about 3 minutes to 15 minutes. ) Should just be the process heated to 110 to 150 degreeC for about 1 second-30 second.

  The primary cooling process (step S3) is performed after the heat sterilization process. The primary cooling step is a step of cooling the heat-sterilized raw material mix to a predetermined temperature. In the primary cooling step, the raw material mix is cooled to a temperature lower than the fermentation promotion temperature range (for example, 30 ° C. to 50 ° C.). In the present invention, a known method can be used for the primary cooling step. For example, in the primary cooling step, the cooling process may be performed by a plate heat exchanger, a tube heat exchanger, a vacuum (reduced pressure) evaporative cooler, or the cooling process may be performed by a tank with a jacket. Specifically, in the primary cooling step, the raw material mix is preferably cooled to 15 ° C. or lower. In the primary cooling step, the raw material mix is preferably cooled to 1 to 15 ° C, more preferably 3 to 10 ° C, and 5 to 8 ° C. Is more preferable.

  In the primary cooling step, it is preferable to rapidly cool the raw material mix at about 100 ° C. whose temperature has been increased in the heat sterilization step to a low temperature (15 ° C. or lower). And, for example, in the primary cooling process, when the sterilization process is a heat treatment, the time for cooling the raw material mix of about 100 ° C. whose temperature has increased in the sterilization process to 15 ° C. is preferably within 10 minutes, It is more preferably within 5 minutes, further preferably within 1 minute, and particularly preferably within 30 seconds. By this cooling step, it is possible to suppress or prevent the protein from being denatured or the sugar from being browned in the raw material mix.

  The starter addition process (step S4) is performed after the cooling process or during the cooling process. The starter addition step is a step of obtaining a fermented milk base material by adding (mixing) lactic acid bacteria starter to the raw material mix. That is, after the heat sterilization process, the lactic acid bacteria starter may be added after the raw material mix has been lowered to the predetermined temperature, or the lactic acid bacteria starter is added while the raw material mix after the heat sterilization process has been lowered to the predetermined temperature. May be. In the present invention, a known method can be used for the starter addition step. However, in the present invention, the lactic acid bacteria starter preferably includes at least Bulgarian bacteria and Thermophilus bacteria. That is, “Bulgaria” is L. bulgaricus, and “Thermophilus” is Streptococcus thermophilus. In the present invention, a known lactic acid bacterium may be added (mixed) in addition to the Bulgarian bacterium and Thermophilus bacterium in the starter addition step. For example, in the starter addition process, gasseri (L. gasseri), lactis (L. lactis), cremollis (L. cremoris), bifidos Bacteria (such as Bifidobacterium) may be added (mixed). The lactic acid bacteria starter is particularly preferably a lactic acid bacteria consisting only of Bulgarian bacteria and Thermophilus bacteria. On the other hand, the addition amount of the lactic acid bacteria starter may be a quantity employed in a known method for producing fermented milk, and is preferably 0.1 to 5% by weight of the fermented milk base material, for example, 0.5 It is more preferably ˜4% by weight, still more preferably 1 to 3% by weight.

  In addition, in the starter addition step, the numbers of bacteria (viable bacteria) of Bulgarian bacteria and Thermophilus bacteria contained in the lactic acid bacteria starter may be any numerical value employed in a known method for producing fermented milk. For example, the ratio of the number of Bulgarian bacteria to the number of Thermofilus bacteria contained in the lactic acid bacteria starter is generally 1: 4 to 1: 5. Specifically, in the starter addition step, the ratio of the number of Bulgarian bacteria when the number of Thermophilus bacteria contained in the lactic acid bacteria starter is 1 (standard) (the number of Bulgarian bacteria / the number of Thermophilus bacteria) The number) may be 0.01 to 0.8, preferably 0.05 to 0.7, more preferably 0.1 to 0.5, and 0.2 to 0.4. More preferably. On the other hand, in the starter addition process, the number of Bulgarian and thermophilus bacteria contained in the lactic acid bacteria starter (viable cell count) can include a larger number of Bulgarian bacteria than the number of thermophilus bacteria in advance. . For example, the ratio of the number of Bulgarian bacteria to the number of Thermophilus bacteria contained in the lactic acid bacteria starter may be 1.0 to 5.0 or 1.5 to 4.0. The number of lactic acid bacteria may be measured according to a known method.

  The primary heating process (step S5) is performed after the starter addition process. The primary heating step is a step of heating the fermented milk base material, which has been cooled to such an extent that lactic acid bacteria starter can be added (1 ° C to 15 ° C), to a fermentation promotion temperature range (for example, 30 ° C to 50 ° C). . Here, “fermentation promotion temperature range” means a temperature at which microorganisms (such as lactic acid bacteria) are activated and fermentation of the fermented milk base proceeds or is promoted. In the present invention, a known method can be used for the primary heating step. For example, in the primary heating step, the heat treatment may be performed by a plate heat exchanger, a tube heat exchanger, or the like, or the heat treatment may be performed by a tank with a jacket. And, for example, 30 ° C. to 50 ° C. is common in the fermentation promotion temperature range of lactic acid bacteria. In addition, specifically, in a heating process, it is preferable that the fermented milk base material is heated to 30 degreeC or more. Further, in the primary heating step, the fermented milk base material is preferably heated to 30 ° C. to 50 ° C., more preferably 33 ° C. to 47 ° C., and 35 ° C. to 44 ° C. More preferably, it is heated.

  Further, in the primary heating step, it is preferable to heat the fermented milk base material whose temperature has been lowered in the primary cooling step to the fermentation promotion temperature range in a predetermined time (in a relatively short time). For example, in the primary heating step, the time for heating the fermented milk base of about 10 ° C. whose temperature has been lowered in the low temperature holding step to the fermentation promotion temperature range is preferably within 1 hour, and within 30 minutes. Preferably, it is within 10 minutes, more preferably within 1 minute. In the primary heating step, the fermented milk base material, whose temperature has been lowered, is directly moved to a fermentation room set at a room temperature of about 30 ° C. to 50 ° C. and heated while gradually raising the temperature in the fermentation room. Temperature treatment can also be performed.

  A primary fermentation process (step S6) is performed after a primary heating process. The primary fermentation step is a step of performing primary fermentation while maintaining the fermented milk base material heated in the fermentation promotion temperature range in the fermentation promotion temperature range. In addition, fermented milk base material does not fully ferment only by a primary fermentation process, and moderate fermentation is complete | finished by performing the secondary fermentation process demonstrated later in addition to this primary fermentation process. In this invention, a well-known method can be used for a primary fermentation process. For example, in the primary fermentation process, the fermentation process may be performed in a fermentation chamber or the like, and the fermentation process may be performed in a jacketed tank. Further, for example, in the primary fermentation process, the temperature in the fermentation chamber (fermentation temperature) is maintained at 30 ° C. to 50 ° C., and any process for fermenting the fermented milk base material in the fermentation chamber may be used. The temperature (fermentation temperature) may be 30 degreeC-50 degreeC, and the process which ferments a fermented milk base material in the tank may be sufficient. Here, in the primary fermentation process, the conditions for fermenting the fermented milk base should be adjusted as appropriate in terms of the fermentation temperature, fermentation time, etc., taking into account the raw material mix, the type and quantity of lactic acid bacteria, and the flavor and texture of the fermented milk. That's fine. Specifically, in the primary fermentation process, the fermented milk base material is preferably held at 30 ° C. or higher. Furthermore, in the primary fermentation process, the fermented milk base material is preferably held at 30 ° C to 50 ° C, more preferably held at 33 ° C to 47 ° C, and held at 35 ° C to 44 ° C. More preferably. Further, specifically, in the primary fermentation process, it is preferable that the fermented milk base material be maintained in the state of the fermentation promotion temperature range for 1 hour or more. And in a fermentation process, it is preferable that the period (fermentation time) which hold | maintains a fermented milk base material is 1 hour-10 hours, It is more preferable that it is 1.5 hours-6 hours, 2 hours-4 hours More preferably.

  Moreover, a primary fermentation process is complete | finished when the pH of a fermented milk base material falls to the predetermined value, and transfers to a subsequent secondary heating process and heat processing process. The standard pH for shifting from the primary fermentation process to the secondary heating process and the heat treatment process is preferably 5.2 to 4.3, more preferably 5.1 to 4.5, and more preferably 5. It is especially preferable that it is 0-4.6. In the primary fermentation step, the fermentation may proceed while measuring the pH of the fermented milk base material, and the primary fermentation may be terminated when a predetermined pH is reached. In order to produce a refreshing flavor while suppressing the acidity of the fermented milk obtained by fermenting the fermented milk base material, the pH of the fermented milk is 4.2 or more, and in particular, the pH is 4.6 to 4.2. It can be said that the range is preferable. In the present invention, the primary fermentation process is terminated immediately before the final pH range of the fermented milk (pH 4.6 to 4.2), and the process proceeds to the secondary heating process and the heat treatment process. As a result, the pH of the fermented milk can be kept in the target range (pH 4.6 to 4.2) for a long time. As a result, the fermented milk rich in flavor with suppressed acidity can be stored for a long period of time, and further, the fermented milk can be concentrated while suppressing the occurrence of acidity.

  In this specification, the pH is measured according to the following method. That is, using a glass electrode type pH meter (HM-30R, manufactured by Toa DKK, with temperature calibration function), the glass electrode is inserted into 100 g of the sample, and when the value becomes constant, the measured value is read to obtain the pH of the sample. .

  The secondary heating process (step S7) is performed after the primary fermentation process. In the secondary heating step, the fermented milk base material that has undergone primary fermentation based on the predetermined pH is heated to a medium to high temperature range (specifically, 53 to 63 ° C.) suitable for the subsequent heat treatment step. It is a process. In the secondary heating step, as in the primary fermentation step, heat treatment may be performed by a plate heat exchanger, a tube heat exchanger, or the like, or heat treatment may be performed by a jacketed tank. In the secondary heating step, it is preferable to heat the fermented milk base in the fermentation promotion temperature range to a medium to high temperature range in a predetermined time (relatively short time). For example, in the secondary heating step, the time for heating the fermented milk base material in the fermentation promotion temperature range to the middle to high temperature range is preferably within 1 hour, preferably within 30 minutes, and 10 minutes. Is more preferably within 1 minute, and particularly preferably within 1 minute.

  Moreover, it is preferable to perform a secondary heating process continuously with a primary fermentation process. That is, it is good to perform a secondary heating process, without reducing the temperature of the fermented milk base material which exists in a fermentation promotion temperature range by a primary fermentation process. For this reason, a fermented milk base material is not cooled between a primary fermentation process and a secondary heating process. Thereby, fermented milk can be manufactured efficiently in a short time while maintaining the vitality of the lactic acid bacteria starter. Conventionally, it has been thought that such a heating treatment is not preferable because further heating of the fermented milk base material during the fermentation process leads to deterioration of the yogurt tissue. By performing the heat treatment under the conditions (temperature and time), there is no problem in the flavor of the fermented milk finally obtained even if the fermented milk base is further heated during the fermentation process.

  The heat treatment process (step S8) is performed after the secondary heating process. The heat treatment step is a step of holding the fermented milk base material in the middle of fermentation in a medium to high temperature range of 53 to 63 ° C. higher than the fermentation promotion temperature range for a predetermined time. That is, when the pH of the fermented milk base finally reaches just before the target pH range (pH 4.6 to 4), the primary fermentation process is terminated, and the heat treatment process in the middle and high temperature range is started. . The timing for starting the heat treatment step (that is, the timing for ending the primary fermentation step) is preferably when the fermented milk base has reached pH 6 to 4, more preferably pH 5.8 to 4.1, and pH 5.5. To 4.2 is more preferred, pH 5.2 to 4.3 is more preferred, and pH 5.0 to 4.6 is particularly preferred. Among them, the timing for starting the heat treatment step is more preferably in the vicinity of pH 4.6, that is, pH 4.7 to 4.5. In addition, the heating temperature and heating time in the heat treatment step are set to a temperature and time that do not completely kill the lactic acid bacteria starter (particularly Bulgarian bacteria and Thermofilus bacteria) contained in the fermented milk base material. Specifically, the heating temperature in the heat treatment step is 53 to 63 ° C, particularly preferably 53 to 60 ° C, and more preferably 53 to 55 ° C. The heating time in the heat treatment step is 2 to 30 minutes, particularly preferably 5 to 30 minutes, may be 10 to 30 minutes or 15 to 30 minutes, and may be 20 to 30 minutes or 25 to 25 minutes. More preferably, it is 30 minutes. In the heat treatment step, as in the secondary heating step, the heat treatment may be performed by a plate heat exchanger, a tube heat exchanger, or the like, or the heat treatment may be performed by a tank with a jacket.

  Even if the fermented milk base material is further heated in the middle of the fermentation process by carrying out an appropriate heat treatment under the above heating conditions (temperature / time), there is a problem with the flavor of the fermented milk finally obtained. It can be avoided. Moreover, as for the fermented milk base material in the primary fermentation process, and the fermented milk base material in the heat processing process, it is preferable that the temperature difference is 3-33 degreeC, and it is 5-30 degreeC or 10-25 degreeC. More preferably, it is 13-23 degreeC. If the temperature difference of the fermented milk base material is large between the primary fermentation step and the heat treatment step (for example, exceeding 40 ° C), many lactic acid bacteria starters in the fermented milk base material will die or the vitality will be remarkable. There is concern about the decline. If it does so, there exists a problem that fermentation of a fermented milk base material will not be performed moderately in a subsequent secondary fermentation process. For this reason, the load given to the lactic acid bacteria starter in the fermented milk base material is reduced by suppressing the temperature difference of the fermented milk base material to an appropriate range (for example, 33 ° C. or less) between the primary fermentation process and the heat treatment process. Can maintain vitality.

  FIG. 2 schematically shows the effect of the heat treatment step in the present invention. In FIG. 2, graph (1) shows that when the final target pH is in the range of 4.6 to 4.2, the heat treatment is performed immediately before the pH of the fermented milk base reaches the target pH. The transition of pH when performed is shown, and graph (2) shows the transition of pH when heat treatment is not performed. In addition, the example shown in FIG. 2 assumes a case where the lactic acid bacteria starter consists of only Bulgarian bacteria and Thermophilus bacteria. As shown in FIG. 2, when heat treatment is performed on the fermented milk base material for a predetermined time in a medium to high temperature range, the pH of the fermented milk base material is a target range (pH 4.6 to 4.2). Will stay for a long time. For this reason, by performing such heat treatment, it becomes possible to suppress the sourness of the finally obtained fermented milk even when stored for a long time. Moreover, since it becomes possible to preserve | save a fermented milk base material for a long period in the range of pH 4.6-4.2, it was a case where concentrated fermented milk was manufactured by lengthening the secondary fermentation period of a fermented milk base material. However, the acidity of the obtained concentrated fermented milk can be suppressed. In addition, as shown in FIG. 2, when the heat treatment is performed immediately before pH 4.6, the time until the pH of the fermented milk base material reaches 4.6 is the case where heat treatment is performed and the case where heat treatment is not performed. It can be seen that there is no significant difference. That is, by performing the heat treatment immediately before pH 4.6, it is possible to avoid that the fermentation time until the end of the primary fermentation is significantly delayed. For this reason, even when it heat-processes, it becomes possible to manufacture fermented milk efficiently. Thus, by heat-treating the lactic acid bacteria substrate in a predetermined pH range, the fermentation rate of the fermented milk is maintained in the first half of the fermentation, and the pH reduction is effectively suppressed in the second half of the fermentation. be able to.

  In the case where the lactic acid bacteria starter consists only of Bulgarian bacteria and Thermophilus bacteria, it is preferable that the start time of the heat treatment step, the heating temperature, and the heating time are as follows. That is, the start time of the heat treatment process is the time when the pH of the fermented milk base material is around 4.6 (pH 4.7 to 4.5), and the heating temperature is around 55 ° C. (53 to 57 ° C.). Yes, the heating time is preferably 15 to 30 minutes. By performing the heat treatment step under such conditions, the fermentation time in the first half of the fermentation can be shortened, and the pH can be suppressed particularly effectively in the second half of the fermentation.

  The secondary cooling process (step S9) is performed after the heat treatment process. The secondary cooling step is a step of cooling the fermented milk base material heated to the middle to high temperature range in the heat treatment step again to the fermentation promotion temperature range (for example, 30 ° C. to 50 ° C.). In the secondary cooling process, as in the primary cooling process, the plate-type heat exchanger, tube-type heat exchanger, and vacuum (reduced pressure) evaporative cooler may be used for cooling, and the jacketed tank is used for cooling. Also good. Moreover, in a secondary cooling process, it is preferable to cool the temperature of the fermented milk base material which rose to the middle-high temperature range to the fermentation promotion temperature range in a short time. For example, the time of the secondary cooling step is preferably within 10 minutes, more preferably within 5 minutes, further preferably within 1 minute, and particularly preferably within 30 seconds.

  The secondary fermentation process (step S10) is performed after the secondary cooling process. The secondary fermentation step is a step of subjecting the fermented milk base material cooled from the middle to high temperature range to the fermentation promotion temperature range to secondary fermentation while maintaining the fermentation fermentation temperature range. In the secondary fermentation step after the heat treatment step, sufficient fermentation of the fermented milk base is completed, and as a result, fermented milk is obtained. Similar to the primary fermentation process, the secondary fermentation process may be performed by a fermentation chamber or the like, or by a tank with a jacket. In the secondary fermentation process, the conditions for fermenting the fermented milk base material may be adjusted as appropriate, such as the fermentation temperature and fermentation time, taking into account the type and quantity of the raw material mix and lactic acid bacteria, and the flavor and texture of the fermented milk. . Specifically, in the secondary fermentation process, it is preferable that the fermented milk base is held at 30 ° C. or higher. Furthermore, in the secondary fermentation step, the fermented milk base material is preferably held at 30 ° C to 50 ° C, more preferably held at 33 ° C to 47 ° C, and held at 35 ° C to 44 ° C. More preferably. Further, specifically, in the secondary fermentation process, it is preferable that the fermented milk base material be maintained in the state of the fermentation promotion temperature range for 1 hour or more. In particular, the secondary fermentation process is preferably performed for a longer time than the above-described primary fermentation process. For example, the period (fermentation time) for holding the fermented milk base material in the secondary fermentation process is preferably 5 hours or more, 8 hours or more, or 10 hours or more.

  The secondary fermentation process may be either a post-fermentation process or a pre-fermentation process. When performing the post-fermentation treatment, the fermented milk base material is subjected to secondary fermentation after filling the fermented milk base material into a container for actually selling as a product. For example, when post-fermentation treatment is performed, fermented milk (fermented milk card) that is an intermediate product obtained by fermenting a container (sealed) filled with a fermented milk base material by leaving it in a fermentation chamber or the like Is cooled in a re-cooling step described later, and fermented milk (set type yogurt, plain type yogurt) as a final product may be obtained. Moreover, when performing a pre-fermentation process, before filling the fermented milk base material into the container for actually selling as a product, fermented milk base material is subjected to secondary fermentation. For example, when pre-fermentation is carried out, the fermented milk (fermented milk card), which is the intermediate product obtained by fermenting by leaving a tank with a jacket filled with a fermented milk base, for example, is crushed or finely divided. After cooling, it is cooled in the re-cooling process described later, and if necessary, after mixing pulp, vegetables, fruit juice, vegetable juice, jam, sauce, preparation, etc., it is filled into a (sealed) container, and finally What is necessary is just to obtain fermented milk (soft type yogurt, drink type yogurt) which is a product.

  Moreover, according to this invention, long-term fermentation is possible in the secondary fermentation process, suppressing the raise of the acidity of a fermented milk base material. For this reason, this invention is suitable for manufacture of the concentrated fermented milk which suppressed acidity. Therefore, in the secondary fermentation process, a fermented milk base material may be left still, and a concentration process for separating the fermented milk base material into a light liquid (whey) and a heavy liquid (concentrated fermented milk) may be performed. After the separation step, fermented milk (concentrated fermented milk) in which milk components are concentrated can be obtained by removing the light liquid from the fermented milk base material. “Standing” as used herein means that the fermented milk base can be separated into a light liquid with a heavy mass and a heavy liquid with a large mass in a natural state without stirring or mixing the fermented milk base material. It means to keep the material quietly without applying external pressure. When performing such a concentration process, it is preferable that the temperature of the fermented milk base material in the secondary fermentation process is in a fermentation acceleration temperature range of 30 ° C to 50 ° C (preferably 43 to 47 ° C). In the secondary fermentation process, the temperature of the fermented milk base material can be cooled to, for example, 10 ° C. or less. In the present invention, the concentration step is not an essential step, and ordinary fermented milk (yogurt) that does not undergo the concentration step can also be produced.

  In addition, the secondary fermentation process may be completed when the pH of the fermented milk base material is lowered to a predetermined value. It is preferable that pH used as the reference | standard which complete | finishes a secondary fermentation process is 4.4-4.2. In particular, even when the fermentation time in the secondary fermentation process is a long period of 5 hours or more, 8 hours or more, or 10 hours or more, the pH of the fermented milk base material is preferably not lower than 4.2. . As described above, by performing the heat treatment step before the secondary fermentation step, it is possible to perform a long-term fermentation while suppressing a decrease in pH. The secondary fermentation process ends after a lapse of a predetermined time and when the pH of the fermented milk base material is lowered to a predetermined value.

  The tertiary cooling process (step S11) is performed after the secondary fermentation process. A tertiary cooling process is a process of cooling fermented milk (especially concentrated fermented milk) obtained by secondary fermentation. In the tertiary cooling step, the progress of fermentation is suppressed by lowering the temperature of the fermented milk. At this time, in the tertiary cooling step, the fermented milk is cooled to a temperature lower than the fermentation promotion temperature range. In the present invention, a known method can be used for the tertiary cooling step. For example, in the tertiary cooling process, the cooling process may be performed by a refrigerator room or a freezer room, and the cooling process may be performed by a plate heat exchanger, a tube heat exchanger, or a tank with a jacket. Specifically, it is preferable that the fermented milk is cooled to 15 ° C. or lower in the tertiary cooling step. In the tertiary cooling step, the fermented milk is preferably cooled to 1 to 15 ° C, more preferably 3 to 10 ° C, and 5 to 8 ° C. Is more preferable. By cooling the fermented milk to a temperature suitable for food by this tertiary cooling process, it is possible to suppress or prevent changes in flavor (such as acidity), texture (such as touch of tongue) and physical properties (such as hardness) of fermented milk. it can. The fermented milk after the tertiary cooling step can be stored in a refrigerator or the like and stored for a long time at a low temperature of 3 ° C to 10 ° C.

  Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the following examples, and various improvements based on known methods can be added.

1. Fermentability of yogurt
[Examples 1-1 to 1-13]
Non-fat dry milk: 100 g and tap water: 900 g were mixed to prepare a yogurt mix. The yogurt mix was sterilized by heating to a temperature of 95 ° C., and then cooled to 10 ° C. Then inoculate the yogurt base with 2% by weight of lactic acid bacteria starter containing Bulgarian bacteria (L.bulgaricus OLL1171 (NITE BP-01569)) and Thermophilus (S.thermohilus OLS3615 (NITE BP-01696)). Obtained. Thereafter, the yogurt base was allowed to stand at 40 ° C. until it was lowered to a predetermined “heat treatment starting pH” for primary fermentation. The yogurt base after the primary fermentation was heat-treated at a predetermined “treatment time” and “treatment temperature”. Thereafter, the yogurt base after the heat treatment was cooled and subjected to secondary fermentation at 40 ° C. until the pH decreased to 4.40 to obtain fermented milk as an example of the present invention. Here, in Examples 1-1 to 1-13, as shown in Table 1 and Table 2, the heat treatment conditions of “heat treatment start pH”, “treatment time”, and “treatment temperature” were changed, respectively. The “heat treatment starting pH” according to the example is any one of pH 5.0, pH 4.65, and pH 4.6, and the “treatment time” is 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, or It was either 30 minutes, and the “treatment temperature” was 53 ° C., 55 ° C., or 60 ° C. Table 1 shows the time required for the yogurt-based pH to reach 4.55 to 4.40 in each example. In each Example, Table 2 shows the time required to reach pH 4.55 from the start of fermentation. In addition, the start of fermentation was the time when the inoculation of lactic acid bacteria starter was completed to the raw material mix.

  In addition, Lactobacillus delbrueckii subsp. Bulgaricus OLL1171 was issued on March 13, 2013 at the Japan Institute for Product Evaluation Technology Patent Microorganism Depositary Center (2-5-8 Kazusa Kamashi, Kisarazu City, Chiba Prefecture 292-0818, Japan). , Accession Number: NITE BP-01569 is deposited internationally. Streptococcus thermophilus OLS3615 has been internationally deposited at the National Institute of Technology and Evaluation Patent Microorganisms Deposit Center on August 23, 2013 as accession number: NITE BP-01696.

[Comparative Examples 1-1 and 1-2]
Then, fermented milk used as a comparative example was manufactured on the same conditions as the said Example except the point which did not heat-process in the middle of a yogurt base fermentation. That is, skim milk powder: 100 g and tap water: 900 g were mixed to prepare a yogurt mix, and this yogurt mix was sterilized by heating to a temperature of 95 ° C., and then cooled to 10 ° C. Then inoculate the yogurt base with 2% by weight of lactic acid bacteria starter containing Bulgarian bacteria (L.bulgaricus OLL1171 (NITE BP-01569)) and Thermophilus (S.thermohilus OLS3615 (NITE BP-01696)). Obtained. Thereafter, the yogurt base was fermented at 40 ° C. until the pH decreased to 4.40 to obtain fermented milk as a comparative example. Table 1 shows the time required for the yogurt-based pH to reach 4.55 to 4.40. Table 2 shows the required time from the start of fermentation until reaching pH 4.55.

  As in Examples 1-1 to 1-13 shown in Table 1 above, when the heat treatment for 5 to 30 minutes in the middle to high temperature range at 53 to 60 ° C. is performed on the yogurt base in the middle of fermentation, the latter half of fermentation The required time from pH 4.55 to pH 4.40 in the season was 1.9 hours at the shortest and 7.4 hours at the longest. In each example, compared with Comparative Example 1-1 in which heat treatment is not performed and Comparative Example 1-2 in which heat treatment is performed at 50 ° C., the required time from pH 4.55 to pH 4.40 is at least about twice or more. Successfully extended.

  In addition, as in Examples 1-1 to 1-13 shown in Table 2 above, when the yogurt base in the middle of fermentation was subjected to heat treatment for 5 to 30 minutes in the middle to high temperature range of 53 to 60 ° C. Even so, the time required to reach pH 4.55 in the first half of the fermentation was 3.4 hours at the shortest and 6.3 hours at the longest. Considering that the required time to H4.55 in Comparative Examples 1-1 and 1-2 is 3.5 hours and 3.6 hours, even when heat treatment is performed as in each Example , The fermentation rate in the first half of the fermentation was not significantly delayed. In particular, Examples in which the time required to H4.55 is 4.5 hours or less (Examples 1-1, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1 -11, 1-12, 1-13), and it can be said that these examples can produce fermented milk as efficiently as the comparative examples.

  Moreover, among various Examples, Examples 1-8, 1-9, 1-11, 1-12, and 1-13 require 5 hours or more from pH 4.55 to pH 4.40. In addition, the time required from the start of fermentation to pH 4.55 was 4.1 hours or less. From these facts, these examples are particularly preferable examples because the fermentation rate of the fermented milk can be maintained in the first half of the fermentation while the pH reduction can be effectively suppressed in the second half of the fermentation. It can be said.

  Then, the result of the sensory evaluation about the sourness and aroma of fermented milk is shown in the following Table 3 and Table 4. The sensory evaluation evaluated the fermented milk of Examples 1-1 to 1-13 and the fermented milk of Comparative Example 1-2 in comparison with the fermented milk of Comparative Example 1-1.

  As shown in Table 3 and Table 4 above, it was confirmed that the sourness and aroma of the fermented milk decreased in any of the examples. Therefore, it was confirmed that the flavor of the obtained fermented milk is improved by performing heat treatment under predetermined conditions during fermentation.

2. Survival rate of lactic acid bacteria and pH change of fermented milk [Examples 2-1 to 2-3]
A raw material mix having a milk fat content of 6% by weight and a protein content of 8% by weight was prepared. The raw material mix was sterilized by heating to a temperature of 95 ° C, and then cooled to 10 ° C. Thereafter, a lactic acid bacterium starter (Bulgaria bacterium and thermophilus bacterium isolated from Meiji Bulgaria yogurt LB81 plain) containing Bulgaria bacterium and Thermophilus bacterium was inoculated into the yogurt mix at 2% by weight to obtain a yogurt base. Thereafter, the yogurt base was allowed to stand at 43 ° C. until the pH decreased to 4.6, and was subjected to primary fermentation. The yogurt base after the primary fermentation was heat-treated for 2 minutes at a treatment temperature of 59 ° C, 60 ° C, or 62 ° C. Thereafter, the yogurt base after the heat treatment was cooled and subjected to secondary fermentation, and allowed to stand after reaching 10 ° C. For each example, fermented milk was applied to each of 24 hours, 7 days (168 hours), 17 days (408 hours), 24 days (576 hours), 35 days (840 hours), and 45 days (1080 hours). The total number of lactic acid bacteria contained and the pH of the fermented milk were measured. The results are shown in Table 5.

[Comparative Example 2]
Then, fermented milk used as a comparative example was manufactured on the same conditions as the said Example except the point which did not heat-process in the middle of a yogurt base fermentation. That is, a raw material mix having a milk fat content of 6% by weight and a protein content of 8% by weight was prepared. The raw material mix was sterilized by heating to a temperature of 95 ° C, and then cooled to 10 ° C. Thereafter, a lactic acid bacterium starter (Bulgaria bacterium and thermophilus bacterium isolated from Meiji Bulgaria yogurt LB81 plain) containing Bulgaria bacterium and Thermophilus bacterium was inoculated into the yogurt mix at 2% by weight to obtain a yogurt base. Thereafter, the yogurt base was allowed to stand at 43 ° C. until the pH decreased to 4.6, and was subjected to primary fermentation. Thereafter, the yogurt base was cooled to 10 ° C. and allowed to stand for secondary fermentation. Two types of fermented milk having the same conditions were prepared. For each comparative example, the total number of lactic acid bacteria contained in the fermented milk and the pH of the fermented milk were measured. The results are shown in Table 5.

  As shown in Table 5 above, in Examples 2-1 to 2-3, compared to Comparative Example 2, the pH of fermented milk is not greatly reduced even when stored in a refrigerator for a long period of time. For example, even after 45 days, the fermented milk of the example maintains pH 4.20 or higher, and it can be said that the acidity is suppressed as compared with the comparative example. Overall, according to the examples, the increase in pH was successfully suppressed by about 0.20 to 0.30 as compared with the comparative examples. Therefore, it was confirmed that the increase in pH during long-term storage can be effectively suppressed by performing heat treatment during fermentation.

  The present invention relates to a method for producing fermented milk such as yogurt. Therefore, the present invention can be suitably used in the manufacturing industry of fermented milk such as yogurt.

Claims (10)

A primary fermentation process in which a fermented milk base material in which lactic acid bacteria starter is added to the raw material mix is subjected to primary fermentation in a fermentation promotion temperature range;
A heat treatment step of maintaining the fermented milk base material after the primary fermentation step in a medium to high temperature range of 53 to 63 ° C., which is higher than the fermentation promotion temperature range, for a certain period of time;
A secondary fermentation step in which the fermented milk base material after the heat treatment step is subjected to secondary fermentation in the fermentation promotion temperature range. The manufacturing method according to claim 1, wherein the heat treatment step is started when the pH of the fermented milk base material is 6 to 4 in the primary fermentation step. The manufacturing method according to claim 2, wherein in the heat treatment step, the time for holding the fermented milk base material in the medium-high temperature range is 2 to 30 minutes. The fermentation promotion temperature range is 30 to 50 ° C.,
The manufacturing method according to claim 3, wherein after the primary fermentation step, the fermented milk base material is heated to the medium-high temperature range without being cooled. The manufacturing method according to claim 4, wherein in the secondary fermentation step, the time required for the pH of the fermented milk base material to change from 4.6 to 4.4 is 1.9 hours or more. The manufacturing method according to claim 5, wherein a required time from the start of the primary fermentation process until the pH of the fermented milk base material becomes 4.6 is 30 hours or less. The manufacturing method according to claim 6, wherein the lactic acid bacterium starter includes a Bulgarian bacterium and a Thermophilus bacterium. The manufacturing method according to claim 1, wherein the pH of the fermented milk base material after 7 days from the start of the primary fermentation process is 4.2 or more. The production method according to claim 7, wherein the total number of lactic acid bacteria in the fermented milk base material after 35 days from the start of the primary fermentation process is 1.0 × 10 ⁷ cfu / g or more. A heat sterilization process for heat sterilizing the raw material mix;
A primary cooling step for cooling the raw material mix after the heat sterilization step;
A starter addition step of obtaining the fermented milk base material by adding the lactic acid bacteria starter to the raw material mix during the primary cooling step or after the primary cooling step;
A primary heating step of heating the fermented milk base material after the starter addition step to the fermentation promotion temperature range;
A secondary heating step of heating the fermented milk base material after the primary fermentation step to the medium-high temperature range;
The manufacturing method according to claim 1, further comprising a secondary cooling step of cooling the fermented milk base material after the heat treatment step to the fermentation promotion temperature range.

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