JP7025842B2 - Method for producing low-sour fermented milk - Google Patents

Description

The present invention relates to a method for producing fermented milk. Specifically, the present invention relates to a method for producing fermented milk in which an increase in sourness during fermentation is suppressed.

Fermented milk is made from milk or milk containing non-fat milk solids equal to or higher than this in Japan's "Ministry Ordinance on Ingredient Standards for Milk and Milk Products" (hereinafter referred to as "Ministry Ordinance for Milk, etc.") using lactic acid bacteria or yeast. It is defined as fermented, pasty or liquid, or frozen. 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 mainly obtained by filling a container and then fermenting the raw material mix and solidifying it in the container. Soft yogurt is obtained by fermenting the raw material mix, crushing the curd in a large tank or the like, mixing it with pulp or sauce as necessary, and then filling it in a container. Drink yogurt can be obtained by finely crushing the above-mentioned set type or soft yogurt with a homogenizer or the like to make it liquid, and if necessary, mixing it with pulp or sauce and then filling it in a container.

In addition, according to the ingredient standards of the Japanese Ministry of Milk, fermented milk must have a non-fat milk solid content of 8.0% or more and a total lactic acid bacteria count of 1.0 x ¹⁰⁷ cfu / g or more. It has been decided. Furthermore, the international standard for yogurt by FAO / WHO also stipulates that a large amount of microorganisms (Bulgarian bacteria, Thermophilus bacteria) must survive in the final product.

As described above, fermented milk contains a large amount of live bacteria such as lactic acid bacteria. Therefore, when fermented milk (or the 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 acidity becomes stronger. In this way, when fermented milk is stored for a long period of time, the pH will decrease over time compared to the one immediately after production, so it is difficult to keep the flavor and quality of fermented milk constant for a long period of time. Was there.

Various methods have been conventionally proposed to solve the above-mentioned problem of lowering the pH of fermented milk. As means for suppressing the increase in acidity 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 temperature zone after fermentation is completed. (Patent Document 3) and the like are known.

Japanese Unexamined Patent Publication No. 10-262550 Japanese Unexamined Patent Publication No. 2000-270844 Japanese Patent Application Laid-Open No. 2003-259802

However, in the conventional method disclosed in the above patent documents and the like, a new additive such as peroxidase is further added, applicable lactic acid bacteria are limited, or a new cooling step such as ice temperate aging is introduced. This causes problems such as complicated manufacturing.

In addition, in the case of industrial mass production of fermented milk, considering the production efficiency, the fermentation rate of the raw material mix is high (the fermentation time is short) 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, so that when the fermented milk is stored for a long period of time, there is a problem that the pH is further lowered and the degree of acidity becomes stronger in the latter half of the fermentation. .. To solve this problem, no technique has been proposed that can efficiently suppress the decrease in pH in the latter half of fermentation while maintaining the fermentation rate in the first half of fermentation at a rate suitable for mass production of fermented milk. ..

In addition, especially in concentrated fermented milk represented by Greek yogurt, the concentration process of allowing the fermented milk to stand still and separating it into a light liquid (whey) and a heavy liquid (concentrated fermented milk) requires several hours. As the fermentation progresses, there is a problem that the acidity of the final product becomes stronger. As a countermeasure against such a problem, fermentation can be suppressed by lowering the temperature of the fermented milk before concentration in the concentration step, but the separation efficiency of the light liquid and the heavy liquid is extremely lowered. In addition, as another measure, there is a method of using a lactic acid bacterium starter with a low acid production capacity, but the difference in pH between the concentrated fermented milk at the start of concentration and immediately before the end of concentration becomes large, 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. Therefore, when considering the industrial production of concentrated fermented milk, a lactic acid bacterium 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. Is desirable. However, under such conditions, fermentation of fermented milk proceeds in the concentration step, and the acidity of the final product (concentrated fermented milk) becomes stronger. Thus, it is difficult to suppress the acidity and fermented odor of concentrated fermented milk.

Therefore, the present invention basically provides a method for producing fermented milk that can effectively suppress a decrease in pH in the latter half of fermentation while maintaining the fermentation rate of fermented milk in the first half of fermentation. The purpose is. Further, in the present invention, for example, in producing concentrated fermented milk, a lactic acid bacterium 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 step. Even in this case, the purpose is to obtain concentrated fermented milk in which the decrease in pH is suppressed in the concentration step and the acidity and fermented odor are suppressed.

As a result of diligent studies on the means for solving the problems of the above-mentioned conventional inventions, the inventors of the present invention first ferment the fermented milk base material in the fermentation promotion temperature range, and then the temperature is higher than that in the fermentation process. By performing heat treatment to maintain for a certain period of time in the medium and high temperature range of 53 to 63 ° C, and then performing secondary fermentation again in the fermentation promotion temperature range, the fermentation rate in the first half of fermentation is maintained and the pH is lowered in the second half of fermentation. It was found that the fermentation process can be effectively suppressed. Furthermore, it has been found that if such a fermentation technique is developed, for example, it is possible to efficiently produce concentrated fermented milk in which the decrease in pH in the concentration step is suppressed and the acidity and fermented odor are suppressed. Then, the present inventors have come up with the idea that the problems of the prior art can be solved based on the above findings, 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 step, a heat treatment step, and a secondary fermentation step. The primary fermentation step is a step of primary fermenting a fermented milk base material in which a lactic acid bacterium starter is added to a raw material mix 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-high temperature range of 53 to 63 ° C., which is higher than the fermentation promotion temperature range, for a certain period of time. The secondary fermentation step is a step of secondary fermentation of the fermented milk base material after the heat treatment step in the fermentation promotion temperature range. The temperature at which the fermented milk base material is secondarily fermented may be within the fermentation promotion temperature range, and may be different from the temperature at which the fermented milk base material is first fermented.

As in the above step, the fermentation rate in the first half of fermentation is reduced by holding the fermented milk base material in the middle of fermentation for a certain period of time in a medium-high temperature range where the fermentation promotion temperature or higher does not kill the lactic acid bacteria starter. Instead, we succeeded in slowing the fermentation rate in the latter half of fermentation and suppressing the production of acid. This makes it possible to efficiently produce a fermented milk having a good flavor with suppressed acidity and fermented odor. Further, with respect to the problem that it is difficult to keep the quality of fermented milk constant for a long period of time, according to the present invention, it is possible to control the acidity during long-term storage. Furthermore, since it is possible to reduce acidity and fermented odor, other flavor substances added to fermented milk and flavors added by ajunct starters (starters that do not affect curd formation but have a role of adding flavor) 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 even more preferably 5.5 to 4. 2. It is particularly preferable to start at the stage of 5.2 to 4.3. That is, the heat treatment step is executed in the period immediately before the fermentation of the fermented milk base material progresses to some extent and reaches the target pH. By strictly controlling the start time of the heat treatment step in this way, it is possible to effectively suppress the decrease in pH in the latter half of fermentation while maintaining the fermentation rate in the first half of fermentation. That is, if 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 will be delayed in reaching the target value, and thus the production efficiency will decrease. On the other hand, if the heat treatment step is performed after the pH of the fermented milk base material becomes less than 4.3, the pH of the fermented milk drops too much and the acidity and fermented 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, and particularly preferably pH 5. It is advisable to start the heat treatment step in the range of .2 to 4.3.

In the present invention, the time for holding the fermented milk base material in the medium and high temperature range in the heat treatment step is preferably 2 to 30 minutes. If the holding time in the medium-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 bacterium starter in the fermented milk substrate may die. Therefore, it is preferable to control the holding time in the medium and 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 step, 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 is performed in this medium-high temperature range. It is preferable to do. If the fermented milk base material in the fermentation promotion temperature range of 30 to 50 ° C is once cooled and then heated to the medium and high temperature range of 53 to 63 ° C, the temperature difference becomes too large, and lactic acid bacteria in the fermented milk base material. There is concern that many starters will die or that their vitality will be significantly reduced. Then, there is a problem that the fermentation of the fermented milk base material is not appropriately performed in the secondary fermentation step. In addition, if time and energy are consumed in the cooling process before the heat treatment process, the production efficiency will decrease, which is not suitable for industrial production of fermented milk. Therefore, as described above, it is preferable that the primary fermentation step and the heat treatment step are continuously performed without going through the cooling step. Conventionally, it has been considered that such a heating treatment is not preferable because further heating the fermented milk base material in the middle of the fermentation process causes deterioration of the yogurt structure. However, as in the present invention, it is appropriate. By performing the heat treatment under heating conditions (temperature and time), there was no problem with the flavor of the fermented milk finally obtained.

In the present invention, it is preferable that 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. In particular, this required time is preferably 4 hours or more. As an example, in the secondary fermentation step, the fermented milk base material may be allowed to stand at 43 ° C. When the fermented milk base material is fermented without going 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, the required time can be doubled or more by performing the heat treatment step. Therefore, in the secondary fermentation step, the fermented milk base material was allowed to stand at around 40 ° C (about ± 3 ° C), and a concentration step was performed to separate it into a light liquid (whey) and a heavy liquid (concentrated fermented milk). Even in this case, the acidity and fermented odor of the obtained concentrated fermented milk can be suppressed. Therefore, according to the present invention, concentrated fermented milk typified by Greek yogurt can be efficiently produced.

In the present invention, the time required from the start of the primary fermentation step to the pH of the fermented milk base material reaching 4.6 is preferably 30 hours or less, more preferably 8 hours or less, and more preferably 4 hours. The following is particularly preferable. The start of the primary fermentation process is the time when the inoculation of the lactic acid bacterium starter into the raw material mix is completed. As described above, by setting the time from the start of the primary fermentation step (at the completion of inoculation of the lactic acid bacterium starter) to reaching pH 4.6 to 8 hours or less, it is possible to avoid a decrease in the production efficiency of fermented milk. When the fermented milk base material is fermented without going through the heat treatment step, the time required from the start of the fermentation step 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 if 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. It can be maintained at the same speed.

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

In the present invention, when the heat treatment step is started when the pH of the fermented milk base material reaches 4.6 and then cooled to 10 ° C. and the secondary fermentation step is carried out, 7 from the start of the primary fermentation step. The pH of the fermented milk base material after the lapse of days is preferably 4.2 or higher. Further, in this case, it is preferable that the total number of lactic acid bacteria in the fermented milk base material 35 days after the start of the primary fermentation step is 1.0 × ¹⁰⁷ cfu / g or more. As described above, according to the present invention, it can be said that the acidity is suppressed because the pH can be maintained at 4.2 or higher even after the fermented milk is stored for a long period of time. In addition, the total number of lactic acid bacteria (1.0 × ¹⁰⁷ cfu / g or more) specified by the Ordinance of the Ministry of Milk, etc. of Japan can be maintained even after 35 days have passed.

The production method of the present invention further comprises a heat sterilization step of heating and sterilizing the raw material mix, a primary cooling step of cooling the raw material mix after the heat sterilization step, and lactic acid bacteria in the raw material mix during or after the primary cooling step. The starter addition step of adding a starter to obtain a fermented milk base material, the primary heating step of heating the fermented milk base material after the starter addition step to the fermentation promotion temperature range, and the fermented milk base material after the primary fermentation step It is preferable to further include a secondary heating step of heating to a medium-high temperature range and a secondary cooling step of 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 the decrease in pH in the latter half of fermentation while maintaining the fermentation rate of fermented milk in the first half of fermentation. Further, according to the present invention, in producing concentrated fermented milk, a lactic acid bacterium 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 step. Even in this case, it is possible to obtain concentrated fermented milk in which the decrease in pH is suppressed in the concentration step and the acidity and fermented odor are suppressed.

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

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. The present invention is not limited to the form described below, and includes a form appropriately modified by a person skilled in the art from the following form to the extent obvious to those skilled in the art.

In the specification of the present application, the “raw material mix” means a liquid containing milk components such as raw milk, whole fat milk, skim milk, and whey, and is in a state before the starter addition step. Here, raw milk means, for example, animal milk such as milk. In addition to milk components such as raw milk, full-fat milk, skim milk, and whey, the raw material mix includes processed products (for example, full-fat milk powder, full-fat concentrated milk, skim milk powder, skim-fat concentrated milk, condensed milk, whey powder, etc. Contains butter milk, butter, cream, cheese, whey protein concentrate (WPC), whey protein isolate (WPI), α-lactoalbumin (α-La), β-lactoglobulin (β-Lg), etc.) Can be done. The "fermented milk base material (yogurt base)" means the state after adding the lactic acid bacterium starter to the raw material mix. Further, "fermented milk" means a production product in a state after the completion of the fermentation process, which is obtained by fermenting the fermented milk base material. Further, in the specification of the present application, "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 by the present invention as a material for frozen yogurt. It is also possible to use the fermented milk produced by the present invention as a material for cheese. In the present invention, the fermented milk may be any of "fermented milk", "dairy product lactic acid bacteria beverage", "lactic acid bacteria beverage" and the like defined by the Ordinance of the Ministry of Milk and the like.

FIG. 1 is a flow chart showing each step of the manufacturing method according to the 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). It is preferable to include S10) and a tertiary cooling step (step S11).

As shown in FIG. 1, in the production of fermented milk, a raw material mix preparation step (step S1) is first performed. The raw material mix preparation step is a step of preparing a raw material mix that is a material for fermented milk. The raw material mix is also called a yogurt mix. In the present invention, known raw material mixes can be used. For example, the raw material mix may be composed only of raw milk (100% raw milk). In addition to milk components such as raw milk, full-fat milk, skim milk, and whey, the raw material mix includes processed products (for example, full-fat milk powder, full-fat concentrated milk, skim milk powder, skim-fat concentrated milk, condensed milk, and whey powder. , Butter milk, butter, cream, cheese, whey protein concentrate (WPC), whey protein isolate (WPI), α-lactoalbumin (α-La), β-lactoglobulin (β-Lg), etc.) It may be prepared by In addition to milk ingredients, the raw material mix includes soy milk, sugar, sugars, sweeteners, flavors, fruit juices, fruit meat, vitamins, minerals, fats and oils, ceramides, collagen, milk phospholipids, polyphenols, and other foods and food ingredients. It can contain food additives and the like. In addition, the raw material mix can contain pectin, soybean polysaccharide, CMC (carboxymethyl cellulose), agar, gelatin, carrageenan, stabilizers such as gums, thickeners, gelling agents and the like, if necessary. .. In the raw material mix preparation step, it is preferable to slightly sulfurize (crush) fat globules and the like contained in the raw material mix by a homogenization step of homogenizing the raw material mix. By this homogenization step, it is possible to suppress or prevent the separation and floating of the raw material mix, the fermented milk base material, and the fat content of the fermented milk during and after the production 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, the heating temperature and the heating time may be adjusted to the extent that various 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 step, heat treatment may be performed by a plate type heat exchanger, a tube type heat exchanger, a steam injection type heating device, a steam infusion type heating device, an energization type heating device, etc., and a tank with a jacket may be used. Heat treatment may be performed. Then, in the heat sterilization step, when the yogurt is a plain type, a hard type, a soft type, etc., heat treatment such as high temperature short time sterilization treatment (HTST) may be performed, and when the yogurt is a drink type, etc., ultra-high temperature may be performed. Heat treatment such as sterilization treatment (UHT) may be performed. Further, for example, in the heat sterilization step, the high-temperature short-time sterilization treatment (HTST) may be a treatment in which the raw material mix is heated to 80 ° C. to 100 ° C. for about 3 to 15 minutes, and is an ultra-high temperature sterilization treatment (UHT). ) May be a process of heating at 110 ° C to 150 ° C for about 1 to 30 seconds.

The primary cooling step (step S3) is performed after the heat sterilization step. 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 type heat exchanger, a tube type heat exchanger, or a vacuum (decompression) evaporation cooler, or may be performed by a tank with a jacket. Specifically, in the primary cooling step, it is preferable that the raw material mix is cooled to 15 ° C. or lower. In the primary cooling step, the raw material mix is preferably cooled to 1 ° C to 15 ° C, more preferably 3 ° C to 10 ° C, and cooled to 5 ° C to 8 ° C. Is more preferable.

Further, in the primary cooling step, it is preferable to rapidly cool the raw material mix having a temperature of about 100 ° C., whose temperature has risen in the heat sterilization step, to a low temperature (15 ° C. or lower). Then, for example, in the primary cooling step, when the sterilization step is a heat treatment, the time for cooling the raw material mix at about 100 ° C., whose temperature has risen in the sterilization step, 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 denaturation of proteins and the browning of sugars in the raw material mix.

The starter addition step (step S4) is performed after the cooling step or during the cooling step. The starter addition step is a step of adding (mixing) a lactic acid bacterium starter to a raw material mix to obtain a fermented milk base material. That is, after the heat sterilization step, the lactic acid bacterium starter may be added after the raw material mix has dropped to a predetermined temperature, or the lactic acid bacterium starter may be added while the raw material mix after the heat sterilization step has dropped to a predetermined temperature. You may. In the present invention, a known method can be used for the starter addition step. However, in the present invention, it is preferable that the lactic acid bacterium starter contains at least Bulgarian bacteria and Thermophilus bacteria. That is, "Bulgarian bacterium" is Lactobacillus bulgaricus (L. bulgaricus), and "Thermus thermophilus" is Streptococcus thermophilus (S. thermophilus). Further, in the present invention, in the starter addition step, known lactic acid bacteria may be added (mixed) in addition to Bulgarian bacteria and Thermophilus bacteria. For example, in the starter addition step, Lactobacillus gasseri (L. gasseri), Lactococcus lactis (L. lactis), Cremoris (L. cremoris), Bifidobacterium. Bacteria (such as Bifidobacterium) may be added (mixed). The lactic acid bacterium starter is particularly preferably composed of only Bulgarian bacteria and Thermophilus bacteria as the lactic acid bacteria. On the other hand, the amount of the lactic acid bacterium starter added may be any amount as long as it is adopted in a known method for producing fermented milk, and is preferably 0.1 to 5% by weight, for example, 0.5% by weight of the fermented milk base material. It is more preferably to 4% by weight, and even more preferably 1 to 3% by weight.

Further, in the starter addition step, the number of Bulgarian bacteria and Thermophilus bacteria contained in the lactic acid bacterium starter (live number) may be any numerical value adopted in the known method for producing fermented milk. And, for example, the ratio of the number of Bulgarian bacteria and the number of Thermophilus bacteria contained in the lactic acid bacterium 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 (reference) (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. Is more preferable. On the other hand, in the starter addition step, the number of Bulgarian bacteria and Thermophilus bacteria contained in the lactic acid bacterium starter can be increased in advance to the number of Bulgarian bacteria rather than the number of Thermophilus bacteria. .. 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, 1.5 to 4.0, or the like. The number of lactic acid bacteria may be measured according to a known method.

The primary heating step (step S5) is performed after the starter addition step. The primary heating step is a step of heating the fermented milk base material, which has been cooled to the extent that a lactic acid bacterium starter can be added (1 ° C to 15 ° C), to a fermentation promotion temperature range (for example, 30 ° C to 50 ° C). .. Here, the "fermentation promotion temperature range" means a temperature at which microorganisms (lactic acid bacteria, etc.) are activated to promote or promote fermentation of the fermented milk base material. 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 type heat exchanger, a tube type heat exchanger, or the like, or may be performed by a tank with a jacket. And, for example, in the fermentation promotion temperature range of lactic acid bacteria, 30 ° C. to 50 ° C. is common. Specifically, in the heating step, it is preferable that the fermented milk base material is heated to 30 ° C. or higher. 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. It is more preferable that it is heated.

Further, in the primary heating step, it is preferable to heat the fermented milk base material whose temperature has dropped in the primary cooling step to the fermentation promotion temperature range in a predetermined time (relatively short time). For example, in the primary heating step, the time for heating the fermented milk base material having a temperature lowered in the low temperature holding step to about 10 ° C. to the fermentation promotion temperature range is preferably within 1 hour, preferably within 30 minutes. It is preferably within 10 minutes, more preferably within 1 minute, and particularly preferably within 1 minute. In the primary heating step, the fermented milk base material whose temperature has dropped is moved as it is to a fermentation chamber set to a room temperature of about 30 ° C to 50 ° C, and heated while gradually raising the temperature in the fermentation chamber. It is also possible to perform thermal treatment.

The primary fermentation step (step S6) is performed after the primary heating step. The primary fermentation step is a step of primary fermentation while maintaining the fermented milk base material heated in the fermentation promotion temperature range in this fermentation promotion temperature range. The fermented milk base material is not sufficiently fermented only by the primary fermentation step, and appropriate fermentation is completed by performing the secondary fermentation step described later in addition to this primary fermentation step. In the present invention, a known method can be used for the primary fermentation step. For example, in the primary fermentation step, the fermentation process may be performed in a fermentation chamber or the like, or the fermentation process may be performed in a tank with a jacket. Further, for example, in the primary fermentation step, the temperature in the fermentation chamber (fermentation temperature) may be maintained at 30 ° C to 50 ° C, and the fermented milk base material may be fermented in the fermentation chamber. The process may be a process in which the temperature (fermentation temperature) is maintained at 30 ° C. to 50 ° C. and the fermented milk base material is fermented in the tank. Here, in the primary fermentation step, the conditions for fermenting the fermented milk base material should be adjusted appropriately in consideration of the raw material mix, the type and quantity of lactic acid bacteria, the flavor and texture of the fermented milk, and the like. Just do it. Specifically, in the primary fermentation step, it is preferable that the fermented milk base material is held at 30 ° C. or higher. Further, in the primary fermentation step, the fermented milk base material is preferably kept at 30 ° C to 50 ° C, more preferably held at 33 ° C to 47 ° C, and held at 35 ° C to 44 ° C. It is more preferable to have. Specifically, in the primary fermentation step, it is preferable that the fermented milk base material is kept in the state of the fermentation promotion temperature range for 1 hour or more. In the fermentation step, the period for retaining the fermented milk base material (fermentation time) is preferably 1 hour to 10 hours, more preferably 1.5 hours to 6 hours, and 2 hours to 4 hours. Is more preferable.

In addition, the primary fermentation step ends when the pH of the fermented milk base material drops to a predetermined value, and the process proceeds to the subsequent secondary heating step and heat treatment step. The reference pH for shifting from the primary fermentation step to the secondary heating step and the heat treatment step is preferably 5.2 to 4.3, more preferably 5.1 to 4.5, and 5. It is particularly preferably 0 to 4.6. In the primary fermentation step, the fermentation may be advanced 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 suppress the acidity of fermented milk obtained by fermenting the fermented milk base material and to produce a refreshing flavor, the pH of the fermented milk should be 4.2 or higher, especially the pH of 4.6 to 4.2. It can be said that it is preferably in the range of. In the present invention, the primary fermentation step is terminated immediately before the final target pH range of the fermented milk (pH 4.6 to 4.2), and the process proceeds to the secondary heating step and the heat treatment step. This makes it possible to keep the pH of the fermented milk in the target range (pH 4.6 to 4.2) for a long time. As a result, it is possible to store the fermented milk having a rich flavor with suppressed sourness for a long period of time, and further to concentrate the fermented milk while suppressing the generation of sourness.

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

The secondary heating step (step S7) is performed after the primary fermentation step. In the secondary heating step, the fermented milk base material for which the primary fermentation has been completed is heated to a medium-high temperature range (specifically, 53 to 63 ° C.) suitable for the subsequent heat treatment step based on the above-mentioned predetermined pH. It is a process. In the secondary heating step, as in the primary fermentation step, the heat treatment may be performed by a plate type heat exchanger, a tube type heat exchanger, or the like, or may be performed by a tank with a jacket. Further, in the secondary heating step, it is preferable to heat the fermented milk base material in the fermentation promotion temperature range to the medium and 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 medium / high temperature range is preferably 1 hour or less, preferably 30 minutes or less, and 10 minutes. It is more preferably within 1 minute, and particularly preferably within 1 minute.

Further, it is preferable that the secondary heating step is continuously performed with the primary fermentation step. That is, it is preferable to carry out the secondary heating step without lowering the temperature of the fermented milk base material in the fermentation promotion temperature range in the primary fermentation step. Therefore, the fermented milk base material is not cooled between the primary fermentation step and the secondary heating step. As a result, fermented milk can be efficiently produced in a short time while maintaining the vitality of the lactic acid bacterium starter. Conventionally, it has been considered that such a heating treatment is not preferable because further heating the fermented milk base material in the middle of the fermentation process causes deterioration of the yogurt structure. However, as will be described later, appropriate heating is performed. By performing the heat treatment under the conditions (temperature and time), even if the fermented milk base material is further heated in the middle of the fermentation process, there is no problem in the flavor of the finally obtained fermented milk.

The heat treatment step (step S8) is performed after the secondary heating step. The heat treatment step is a step of holding the fermented milk base material in the middle of fermentation in a medium / high temperature range of 53 to 63 ° C., which is higher than the fermentation promotion temperature range, for a predetermined time. That is, when the pH of the fermented milk base material finally reaches the target pH range (pH 4.6 to 4), the primary fermentation step is terminated and the heat treatment step in the medium-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 material reaches pH 6 to 4, more preferably pH 5.8 to 4.1, and pH 5.5. -4.2 is more preferable, pH 5.2 to 4.3 is further preferable, and pH 5.0 to 4.6 is particularly preferable. Among them, the timing for starting the heat treatment step is more preferably around pH 4.6, that is, pH 4.7 to 4.5. The heating temperature and heating time in the heat treatment step are set to such a temperature and time that the lactic acid bacteria starter (particularly Bulgarian bacteria and Thermophilus bacteria) contained in the fermented milk base material is not completely killed. Specifically, the heating temperature in the heat treatment step is 53 to 63 ° C, particularly preferably 53 to 60 ° C, and even 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, and may be 10 to 30 minutes or 15 to 30 minutes, 20 to 30 minutes or 25 to 25 minutes. It is more preferably 30 minutes. In the heat treatment step, as in the secondary heating step, the heat treatment may be performed by a plate type heat exchanger, a tube type heat exchanger, or the like, or may be performed by a tank with a jacket.

By performing an appropriate heat treatment under the above heating conditions (temperature and time), even if the fermented milk base material is further heated during the fermentation process, there is a problem with the flavor of the fermented milk that is finally obtained. It can be avoided to occur. Further, the temperature difference between the fermented milk base material in the primary fermentation step and the fermented milk base material in the heat treatment step is preferably 3 to 33 ° C, preferably 5 to 30 ° C or 10 to 25 ° C. More preferably, it is particularly preferably 13 to 23 ° C. If the temperature difference of the fermented milk base material is large (for example, if it exceeds 40 ° C) between the continuous primary fermentation step and the heat treatment step, many lactic acid bacteria starters in the fermented milk base material will die or the vitality will be remarkable. There is concern that it will decline. Then, there is a problem that the fermentation of the fermented milk base material is not appropriately performed in the subsequent secondary fermentation step. Therefore, by suppressing the temperature difference of the fermented milk base material within an appropriate range (for example, 33 ° C. or less) between the primary fermentation step and the heat treatment step, the load applied to the lactic acid bacterium starter in the fermented milk base material can be reduced. You can maintain your vitality.

FIG. 2 schematically shows the effect of the heat treatment step in the present invention. In FIG. 2, in the graph (1), when the finally target pH is in the range of 4.6 to 4.2, the heat treatment is performed at the timing immediately before the pH of the fermented milk base material reaches the target pH. The transition of the pH when the heat treatment was performed is shown, and the graph (2) shows the transition of the pH when the heat treatment was not performed. The example shown in FIG. 2 assumes that the lactic acid bacterium starter consists of only Bulgarian bacteria and Thermophilus bacteria. As shown in FIG. 2, when the fermented milk base material is heat-treated to be held in a medium-high temperature range for a predetermined time, the pH of the fermented milk base material is in the target range (pH 4.6 to 4.2). Will stay for a long time. Therefore, by performing such a heat treatment, it is possible to suppress the acidity of the finally obtained fermented milk even when it is stored for a long period of time. In addition, since the fermented milk base material can be stored for a long period of time in the range of pH 4.6 to 4.2, there is a case where the secondary fermentation period of the fermented milk base material is lengthened to produce concentrated fermented milk. However, the acidity of the obtained concentrated fermented milk can be suppressed. Further, as shown in FIG. 2, when the heat treatment is performed immediately before the pH 4.6, the time until the pH of the fermented milk base material reaches 4.6 is the time when the heat treatment is performed and the case where the heat treatment is not performed. It can be seen that there is no big difference in. 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. Therefore, even when heat treatment is performed, fermented milk can be efficiently produced. In this way, by heat-treating the lactic acid bacterium base material in a predetermined pH range, the fermentation rate of the fermented milk is maintained in the first half of fermentation, and the decrease in pH is effectively suppressed in the second half of fermentation. be able to.

When the lactic acid bacterium starter consists only of Bulgarian bacteria and Thermophilus bacteria, the start time, heating temperature, and heating time of the heat treatment step are preferably as follows. That is, the start time of the heat treatment step is when the pH of the fermented milk base material reaches around 4.6 (pH 4.7 to 4.5), and the heating temperature is around 55 ° C (53 to 57 ° C). The heating time is preferably 15 to 30 minutes. By performing the heat treatment step under such conditions, it is possible to shorten the fermentation time in the first half of fermentation and particularly effectively suppress the decrease in pH in the second half of fermentation.

The secondary cooling step (step S9) is performed after the heat treatment step. The secondary cooling step is a step of cooling the fermented milk base material heated to the medium / high temperature range again in the heat treatment step 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 cooling process may be performed by a plate heat exchanger, a tube heat exchanger, or a vacuum (decompression) evaporation cooler, and the cooling process is performed by a tank with a jacket. May be good. Further, in the secondary cooling step, it is preferable to cool the temperature of the fermented milk base material, which has risen to the medium and high temperature range, to the fermentation promotion temperature range in a short time. For example, the time of the secondary cooling step is preferably 10 minutes or less, more preferably 5 minutes or less, further preferably 1 minute or less, and particularly preferably 30 seconds or less.

The secondary fermentation step (step S10) is performed after the secondary cooling step. The secondary fermentation step is a step of secondary fermentation while maintaining the fermented milk base material cooled from the medium-high temperature range to the fermentation promotion temperature range in this fermentation promotion temperature range. In the secondary fermentation step after the heat treatment step, sufficient fermentation of the fermented milk base material is completed, and as a result, fermented milk is obtained. In the secondary fermentation step, as in the primary fermentation step, the fermentation treatment may be carried out in a fermentation chamber or the like, or the fermentation treatment may be carried out in a tank with a jacket. In the secondary fermentation step, the conditions for fermenting the fermented milk base material may be appropriately adjusted, such as the fermentation temperature and fermentation time, in consideration of the raw material mix, the type and quantity of lactic acid bacteria, the flavor and texture of the fermented milk, and the like. .. Specifically, in the secondary fermentation step, it is preferable that the fermented milk base material is held at 30 ° C. or higher. Further, in the secondary fermentation step, the fermented milk base material is preferably kept at 30 ° C to 50 ° C, more preferably held at 33 ° C to 47 ° C, and held at 35 ° C to 44 ° C. Is more preferable. Specifically, in the secondary fermentation step, it is preferable that the fermented milk base material is kept in the state of the fermentation promotion temperature range for 1 hour or more. In particular, the secondary fermentation step is preferably carried out for a longer time than the above-mentioned primary fermentation step. For example, the period (fermentation time) for retaining the fermented milk base material in the secondary fermentation step is preferably 5 hours or more, 8 hours or more, or 10 hours or more.

The secondary fermentation step may be either a post-fermentation process or a pre-fermentation process. When performing the post-fermentation process, the fermented milk base material is secondarily fermented after the fermented milk base material is filled in a container for actual sale as a product. For example, when performing post-fermentation processing, fermented milk (fermented milk card), which is an intermediate product obtained by fermenting a (sealed) container filled with a fermented milk base material by allowing it to stand in a fermentation chamber. May be cooled in the recooling step described later to obtain fermented milk (set type yogurt, plain type yogurt) which is the final product. In addition, when the pre-fermentation process is performed, the fermented milk base material is secondarily fermented before the container for actually selling as a product is filled with the fermented milk base material. For example, when pre-fermenting, a tank with a jacket filled with a fermented milk base material is allowed to stand to ferment, and the resulting intermediate product, fermented milk (fermented milk curd), is crushed or finely divided. After fermentation, it is cooled in the recooling step described later, and if necessary, it is mixed with fruit meat, vegetables, fruit juice, vegetable juice, jam, sauce, preparation, etc., and then filled in a (sealed) container for final fermentation. Fermented milk (soft type yogurt, drink type yogurt), which is a product, may be obtained.

Further, according to the present invention, in the secondary fermentation step, long-term fermentation is possible while suppressing an increase in the acidity of the fermented milk base material. Therefore, the present invention is suitable for producing concentrated fermented milk with suppressed acidity. Therefore, in the secondary fermentation step, the fermented milk base material may be allowed to stand still, and a concentration step may be performed in which the fermented milk base material is separated into a light liquid (whey) and a heavy liquid (concentrated fermented milk). By removing the light liquid from the fermented milk base material after the separation step, fermented milk with concentrated milk components (concentrated fermented milk) can be obtained. In addition, "standing" here means fermented milk base to the extent that it can be separated into a light liquid with a light mass and a heavy liquid with a heavy mass in the natural state without stirring or mixing the fermented milk base material. It means to leave the material quietly without applying external pressure. When such a concentration step is performed, the temperature of the fermented milk base material in the secondary fermentation step is preferably in the fermentation promotion temperature range of 30 ° C. to 50 ° C. (preferably 43 to 47 ° C.). In the secondary fermentation step, the temperature of the fermented milk base material can be cooled to, for example, 10 ° C. or lower, but in that case, the separation rate of the light liquid and the heavy liquid becomes significantly slow, which is not preferable. In the present invention, the concentration step is not an essential step, and it is also possible to produce ordinary fermented milk (yogurt) that does not undergo the concentration step.

Further, the secondary fermentation step may be completed when the pH of the fermented milk base material drops to a predetermined value. The reference pH for terminating the secondary fermentation step is preferably 4.4 to 4.2. In particular, even when the fermentation time in the secondary fermentation step is 5 hours or longer, 8 hours or longer, or 10 hours or longer, 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 carry out long-term fermentation while suppressing the decrease in pH. The secondary fermentation step is terminated after a predetermined time has elapsed and when the pH of the fermented milk base material has dropped to a predetermined value.

The tertiary cooling step (step S11) is performed after the secondary fermentation step. The tertiary cooling step is a step of cooling the fermented milk (particularly concentrated fermented milk) obtained by the secondary fermentation. By lowering the temperature of the fermented milk in the tertiary cooling step, the progress of fermentation is suppressed. At this time, in the tertiary cooling step, the fermented milk is cooled until the temperature becomes 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 step, the cooling process may be performed by a refrigerating room or a freezing room, or may be performed by a plate type heat exchanger, a tube type heat exchanger, or a tank with a jacket. Specifically, in the tertiary cooling step, it is preferable that the fermented milk is cooled to 15 ° C. or lower. In the tertiary cooling step, the fermented milk is preferably cooled to 1 ° C to 15 ° C, more preferably 3 ° C to 10 ° C, and cooled to 5 ° C to 8 ° C. Is even 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 the flavor (sour taste, etc.), texture (texture, etc.) and physical properties (hardness, etc.) of the fermented milk. can. The fermented milk after the tertiary cooling step can be stored in a refrigerator or the like and stored at a low temperature of 3 ° C to 10 ° C for a long period of time.

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. 1. Fermentability of yogurt
[Examples 1-1 to 1-13]
A yogurt mix was prepared by mixing 100 g of skim milk powder and 900 g of tap water, and the yogurt mix was sterilized by heating to a temperature of 95 ° C. and then cooled to 10 ° C. Then, inoculate the yogurt mix with a lactic acid bacterium starter containing Bulgarian bacteria (L.bulgaricus OLL1171 (NITE BP-01569)) and Thermophilus bacteria (S.thermohilus OLS3615 (NITE BP-01696)) in 2% by weight to make a yogurt base. Obtained. Then, the yogurt base was allowed to stand at 40 ° C. until the pH was lowered to the predetermined “heat treatment start pH” for primary fermentation. The yogurt base after the primary fermentation was heat-treated at a predetermined "treatment time" and "treatment temperature". Then, the yogurt base after the heat treatment was cooled and secondarily fermented at 40 ° C. until the pH dropped to 4.40 to obtain fermented milk according to an example of the present invention. Here, in Examples 1-1 to 1-13, as shown in Tables 1 and 2, the heat treatment conditions of "heat treatment start pH", "treatment time", and "treatment temperature" were changed, respectively. The "heat treatment start pH" according to the examples is any of pH 5.0, pH 4.65, or 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 either 53 ° C, 55 ° C, or 60 ° C. In each example, the time required for the yogurt-based pH to reach 4.55 to 4.40 is shown in Table 1. In addition, in each example, the time required from the start of fermentation to reaching pH 4.55 is shown in Table 2. The start of fermentation was the time when the inoculation of the lactic acid bacterium starter into the raw material mix was completed.

Lactobacillus delbrueckii subsp. Bulgaricus OLL1171 was sent to the National Institute of Technology and Evaluation Patent Microbial Deposit Center (2-5-8 Kazusakamatari, Kisarazu City, Chiba Prefecture, 292-0818, Japan) on March 13, 2013. ， Deposit number: NITE BP-01569 is internationally deposited. In addition, Streptococcus thermophilus OLS3615 has been internationally deposited with the National Institute of Technology and Evaluation Patent Microorganisms Depositary on August 23, 2013 under the accession number: NITE BP-01696.

[Comparative Examples 1-1, 1-2]
Subsequently, a fermented milk as a comparative example was produced under the same conditions as those in the above-mentioned example, except that the heat treatment was not performed during the fermentation of the yogurt base. That is, 100 g of skim milk powder and 900 g of tap water were mixed to prepare a yogurt mix, and the yogurt mix was sterilized by heating to a temperature of 95 ° C. and then cooled to 10 ° C. Then, inoculate the yogurt mix with a lactic acid bacterium starter containing Bulgarian bacteria (L.bulgaricus OLL1171 (NITE BP-01569)) and Thermophilus bacteria (S.thermohilus OLS3615 (NITE BP-01696)) in 2% by weight to make a yogurt base. Obtained. Then, the yogurt base was fermented at 40 ° C. until the pH dropped 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 time required from the start of fermentation to reaching pH 4.55.

As in Examples 1-1 to 1-13 shown in Table 1 above, when the yogurt base during fermentation is heat-treated to be held in a medium-high temperature range of 53 to 60 ° C. for 5 to 30 minutes, the latter half of fermentation. The time required from pH 4.55 to pH 4.40 in the period was 1.9 hours at the shortest and 7.4 hours at the longest. In each example, the time required from pH 4.55 to pH 4.40 is at least about twice as long as that of Comparative Example 1-1 without heat treatment and Comparative Example 1-2 with heat treatment at 50 ° C. I succeeded in extending it.

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

Further, among various examples, Examples 1-8, 1-9, 1-11, 1-12, and 1-13 set the required time from pH 4.55 to pH 4.40 to 5 hours or more. In addition, the time required from the start of fermentation to pH 4.55 was 4.1 hours or less. From this, these examples are particularly preferable examples because they can effectively suppress the decrease in pH in the latter half of fermentation while maintaining the fermentation rate of fermented milk in the first half of fermentation. It can be said that.

Subsequently, Tables 3 and 4 below show the results of sensory evaluation of the acidity and aroma of fermented milk. In the sensory evaluation, the fermented milk of Examples 1-1 to 1-13 and the fermented milk of Comparative Example 1-2 were evaluated in comparison with the fermented milk of Comparative Example 1-1.

As shown in Tables 3 and 4, it was confirmed that the acidity and aroma of the fermented milk were reduced in each of the examples. Therefore, it was confirmed that the flavor of the obtained fermented milk was improved by performing heat treatment under predetermined conditions during fermentation.

2. 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, and the raw material mix was sterilized by heating to a temperature of 95 ° C. and then cooled to 10 ° C. Then, a yogurt base was obtained by inoculating a yogurt mix with 2% by weight of a lactic acid bacterium starter containing Bulgaria and Thermophilus (Bulgaria and Thermophilus isolated from Meiji Bulgaria Yogurt LB81 plane manufactured by Meiji Co., Ltd.). Then, the yogurt base was allowed to stand at 43 ° C. until the pH dropped to 4.6 for primary fermentation. The yogurt base after the primary fermentation was heat-treated at a treatment temperature of 59 ° C., 60 ° C., or 62 ° C. for 2 minutes. Then, the yogurt base after the heat treatment was cooled to perform secondary fermentation, and the yogurt base was allowed to stand from the time when it reached 10 ° C. For each example, fermented milk for 24 hours, 7 days (168 hours), 17 days (408 hours), 24 days (576 hours), 35 days (840 hours), and 45 days (1080 hours), respectively. The total number of lactic acid bacteria contained and the pH of fermented milk were measured. The results are shown in Table 5.

[Comparative Example 2]
Subsequently, a fermented milk as a comparative example was produced under the same conditions as those in the above-mentioned example, except that the heat treatment was not performed during the fermentation of the yogurt base. 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, and this raw material mix was sterilized by heating to a temperature of 95 ° C. and then cooled to 10 ° C. Then, a yogurt base was obtained by inoculating a yogurt mix with 2% by weight of a lactic acid bacterium starter containing Bulgaria and Thermophilus (Bulgaria and Thermophilus isolated from Meiji Bulgaria Yogurt LB81 plane manufactured by Meiji Co., Ltd.). Then, the yogurt base was allowed to stand at 43 ° C. until the pH dropped to 4.6 for primary fermentation. Then, the yogurt base was cooled to 10 ° C. and allowed to stand for secondary fermentation. Two types of fermented milk under 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, the pH of the fermented milk did not significantly decrease even when refrigerated for a long period of time as compared with Comparative Example 2. For example, even after 45 days have passed, the fermented milk of the example maintains a pH of 4.20 or higher, and it can be said that the acidity is suppressed as compared with the comparative example. As a whole, according to the example, it succeeded in suppressing the increase in pH by about 0.20 to 0.30 as compared with the comparative example. Therefore, it was confirmed that the pH increase 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 (9)

A primary fermentation process in which a fermented milk base material containing a lactic acid bacterium starter added to a raw material mix is first fermented in a fermentation promotion temperature range.
When the pH of the fermented milk base material reaches 4.65 to 4.6, the primary fermentation step is terminated and the fermented milk base material is heated to a temperature higher than that in the fermentation promotion temperature range. A heat treatment process that holds the product in a medium / high temperature range of ~ 63 ° C for 15 to 30 minutes ,
Includes a secondary fermentation step in which the fermented milk base material after the heat treatment step is secondarily fermented in the fermentation promotion temperature range for 1 hour or more.
Method for producing concentrated fermented milk. In the secondary fermentation step, the fermented milk base material is separated into whey and the concentrated fermented milk by allowing it to stand, and then the whey is removed to obtain the concentrated fermented milk.
The manufacturing method according to claim 1. The production method according to claim 2, wherein the time for holding the fermented milk base material in the medium-high temperature region in the heat treatment step is 15 to 30 minutes. The fermentation promotion temperature range is 30 to 50 ° C.
The production 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 production 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 production method according to claim 5, wherein the time required from the start of the primary fermentation step to the pH of the fermented milk base material reaching 4.6 is 30 hours or less. The production method according to claim 6, wherein the lactic acid bacterium starter contains Bulgarian bacteria and Thermophilus bacteria. The production method according to claim 1, wherein the pH of the fermented milk base material after 7 days from the start of the primary fermentation step is 4.2 or more. A heat sterilization process that heats and sterilizes the raw material mix, and
A primary cooling step for cooling the raw material mix after the heat sterilization step, and
A starter addition step of adding the lactic acid bacterium starter to the raw material mix during the primary cooling step or after the primary cooling step to obtain the fermented milk base material.
A primary heating step of heating the fermented milk base material after the starter addition step to the fermentation promotion temperature range, and a primary heating step.
A secondary heating step of heating the fermented milk base material after the primary fermentation step to the medium-high temperature range, and a secondary heating step.
The production 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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