JPS58152444A - Production of sterilized yoghurt - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] The present invention relates to a method for producing sterilized yogurt.

BACKGROUND OF THE INVENTION Yogurt is a form of fermented milk that has been coagulated to a smooth, ream-like or custard-like consistency by lactic acid-producing microorganisms. The structure of natural yogurt uses a matrix of deceased body milk.
Optionally, other ingredients such as stabilizers and sugars are included and Lactobacillus bulgaricus (Lactobacillus bulgaricus)
cillus bulgaricus) and Streptococcus thermophilus
us' chemophAlus) beneficial cultures (
starter), then the pH of the substrate is approximately 4.5.
Requires culturing at approximately 100-1101 until it drops to ~4.3. This pH indicates that the Φ conversion to the desired product, ie yogurt, is complete. The yogurt is then cooled to inhibit or prevent the growth of undesirable microorganisms. The milk matrix and the resulting natural yogurt have a solids content of about 11-13% by weight. Cultivation can be carried out in individual containers in which yogurt is sold, or it can be carried out in vats or similar containers and, after completion, transferred to individual containers in which yogurt is sold. Fruits, fruit bouquets or other flavors may be added to the plain yogurt base. In recent years, the increase in yogurt consumption, especially in North America, has been extremely significant (
For example, between 1960 and 1975, per capita consumption in the United States increased by 483%). Due to the significant increase in demand, yogurt is now manufactured on a large scale and sold through a wide variety of retail outlets, including supermarkets and the like. However, the product is highly perishable, even if
Refrigeration is required for storage, even for a limited period of time, and even under refrigerated conditions, natural yogurt's maximum shelf life is only a few weeks.

As a result, it can only be transported to limited areas. Therefore, many attempts have been made to process yogurt to extend its shelf life and eliminate the need for refrigeration. Such attempts take various forms. For example, in U.S. Pat. No. 3,080,236 (Ferguson), whole milk or skim milk with normal milk solids content is inoculated with a culture, incubated at about 100°F for 12 hours, and the resulting yogurt volume is evaporated. - and then drying in a vacuum dryer to produce instant yogurt that does not require refrigeration and has a long shelf life. This product is
When powdered, at least 10% readily soluble water-soluble starch is necessary to impart sufficient body to the reconstituted yogurt, and various other ingredients, including fats, are mixed to give the product the appearance of yogurt. It gives it flavor. U.S. Pat. No. 4,066,794 (Schut) discloses a similar instant yogurt in which gelling agents or curing agents are said to impart a thixotropic, curd-like consistency to the reconstituted product. By adding at least 5% by weight of sodium alginate and 70% by weight of sugar, the reconstituted yogurt is given body. Another route to extend the shelf life of yogurt is proposed by US IL 3932680 (Egli eL
al).

This patent discloses a method for making pasteurized yogurt.

In this method, sterilized and homogenized milk is concentrated to 10%, 10-12% sugar is added, the mixture is cooled, and a culture of lactic acid bacteria is used to produce 2.5-4% milk at 42-44°C. The resulting yogurt was cultured for hours to pH 4.0 to 4.3.
The base is cooled to 30-20°C. The base is then further cooled to 12-4°C and an effective amount of the following stabilizer is added. Stabilizer A contains 20-30% by weight of emulsifier, 20-40% by weight of carrageenan, 30-40% by weight of carboxymethyl cellulose, 2-3% by weight of whole robin meat or powder and 4-8% by weight of guar meal. do. Stabilizer B is potato starch or other starch, and Stabilizer C contains 75-85% by weight of 60% denatured gelatin and sugar (carrier for dissolving or dispersing proteins).

Then, the obtained mixture is left to stand at 4 to 12°C for 5 to 7 hours to once produce yogurt. Furthermore, transfer this yogurt to a sealed container and place it in an autoclave for 6 to 85 minutes.
The container is subjected to a sterilization operation in which the container is heated at a pressure of up to 2 atmospheres at 0.degree. C. for a period sufficient to sterilize the product and container. It is then cooled under pressure to 10-15°C and at its shallowest point, the container is stored at 4-6°C for 2-4 days. All that can be said is that this method is very complex, time consuming and probably cannot be carried out economically on an industrial scale. In fact, at least in North America, there are currently no pasteurized true yogurt products available on the market (overlays of such products have been attempted and failed over the past few years). Furthermore, it should be noted that the relatively high sugar content and the necessity of cooling before heat treatment to avoid whey syneresis in the final product. A variation of US Pat. No. 3,932,68 LJ is described in US Pat. No. 4,235,934.

The production of heat-treated pasteurized yoghurt is accompanied by a number of CI problems, and the fundamental difficulty, which is also important from a consumer acceptance point of view, is that the body or structure of the yoghurt is exposed to heat and is susceptible to commercial manufacturing operations. Easily disassembled by mechanical action such as pumping required in
It consists of a delicate protein matrix that is easily destroyed. In addition, the unique flavor of yogurt due to heat treatment tends to suffer from serious quality deterioration, and many of the conventional heat-treated yogurt products contain "yoghurt" in the final product.
It is necessary to add ingredients to impart "flavor". Therefore, it is not possible to simply pasteurize standard yogurt to obtain a product that is acceptable to consumers. As is well documented in the prior literature, preserving yogurt flavor and texture is essential to obtaining an acceptable product, and traditional products lack one or, generally, both of these characteristics. Many problems remain.

One object of the present invention is to economically provide a pasteurized or shelf-enhanced natural yogurt that has the flavor and texture of natural yogurt and has a long shelf life without refrigeration.

SUMMARY OF THE INVENTION Culture imitation, when the yogurt base is still at high temperature,
Small amounts of each of carrageenan, citric acid, starch and sugar are added and mixed, and the resulting mixture is subjected to a specific time/temperature treatment, whereby the starch has virtually no appreciable effect. It has been shown that the above objective can be achieved by preconditioning the protein without gelatinization and then subjecting it to a one-step homogenization at a pressure lower than the normal pressure, followed by heating to sterilization temperature. found. If desired, usually
After homogenization and before sterilization of the product, fruit or other usual ingredients imparting flavor, color, etc. to the plain yogurt may be added.

DETAILED DESCRIPTION OF THE INVENTION In one aspect, the present invention provides the steps of: a) maintaining a liquid pore substrate at an elevated temperature for a period sufficient to sterilize it; and (b) cooling the sterilized substrate to an incubation temperature of 100 to 115 degrees Fahrenheit. and Ic) inoculating the substrate with a yogurt culture that produces lactic acid and culturing it until the pH drops to 4.5-4.0 to obtain a yogurt base, (di) the yogurt base is still at a high temperature. The following ingredients: Carrageenan 0.1-0.8% citrate ions 0.05-2.0% starch
0.5-2°5% sugar 2.0
~6.0% and, if necessary, water Milk solids content of the entire mixture is ~10
(e) The obtained natural yogurt can be subjected to protein preconditioning without substantial gelatinization of the starch. if) the mixture is subjected to a high temperature/time treatment of up to about 170°F, 500-1
Homogenize in one step under a pressure of 5 LIOPSi, fgl optionally add flavors and/or fragrances to the homogenized mixture, ih) pasteurize the resulting mixture at a temperature of at least 180° F. A method of making pasteurized yogurt is provided which comprises cooling to below 0.5°F.

The mixing of the yoghurt base and other ingredients in step id) can be advantageously carried out by forming the ingredients into an aqueous slurry. This can reduce the possibility of lump formation and aid in uniform, smooth dispersion. Furthermore, this allows the water contained in the slurry to be mixed with the slurry to reduce the solids content of the resulting yogurt to the normally desired 10-15%.
, (bi23 and lc), preferably 1
It is possible to use milk substrates with a solids content of 5-20%. Increasing the solids content reduces the volume to be processed so that smaller scale and less expensive equipment can be used. Also, greater product throughput can be achieved. In step fdl, when adding and mixing each ingredient dry to the yogurt base, care should be taken to ensure proper dispersion of dry solids throughout the mixture, which is achieved using low intensity mixing action to achieve the desired This can be conveniently achieved by uniform dispersion.

In another wI4, the present invention provides the following methods: (3) holding a liquid pore matrix of about 15-20% by weight of total milk solids at an elevated temperature for a sufficient time to sterilize the sterilized substrate of about 100-115 (c) inoculating the substrate with a yogurt culture that produces lactic acid and culturing until the pH drops to about 4.5-4.0 to obtain a yogurt base; fdl While the yogurt base is still at elevated temperature, carrageenan about 0.1-0.8%, preferably about 0.1-0.5% citrate ions about 0.05-2.0% starch
about 0.5-2.5%, preferably about 0
．． 5-1.5% sugar approximately 2.0-6.0% water
The milk solids content of the entire mixture is approximately 10-1
(e) Adding and mixing an aqueous slurry in an amount such that 5% (all percentages are by weight of the total mixture) The mixture is subjected to a high temperature/time treatment that allows for preconditioning of lfl.
Homogenize in one step under a pressure of 0 psi, (- optionally add flavors and/or fragrances to the homogenized mixture, (h) sterilize the resulting mixture at a temperature of at least 180°F, (il sterilize A method of making pasteurized yogurt is provided which comprises cooling the yogurt to below 85 degrees Fahrenheit.

It is also preferred to add up to 0.5% pectin in step (d).

The product can then be filled in previously sterilized containers under aseptic conditions in a manner known per se.

Various parameters are included, and their criticality in the present invention will be explained below.

Milk Substrate Preferably, the yoghurt obtained according to the invention has a milk solids content similar to natural yoghurt, ie about 11-15% by weight, generally 11-13% by weight. In the manufacture of natural yogurt, the milk matrix usually has a total milk solids content similar to the desired total milk solids content in the final product. However, it has been found that in the method of the present invention, the various ingredients described in step fdl above can be advantageously added and mixed into the yogurt base in the form of an aqueous suspension, i.e. there is no additional water in the system. added, thereby reducing the proportion of milk solids. Therefore, the total milk solids content of the milk matrix before pasteurization and inoculation is approximately 15-20% by weight;
Preferably, good results are obtained at about 17-18% by weight. This relatively high milk solids content can be obtained in several ways. For example, it can be obtained by concentrating the liquid pores by vacuum evaporation or the like, or preferably by adding further milk solids in the form of skimmed milk, evaporated milk, etc.

Typically, these milk solids warm the liquid pores (approximately 1°OoF
) and add. Of course, the milk substrate can be used in normal amounts, e.g.
Contains ~4% milk fat by weight.

The milk matrix having the abovementioned total milk solids content is pasteurized by known methods. For example, according to the VAT method, 175-2
Heat at U O'F for 5-30 minutes.

Of course, shorter times will be employed at higher temperatures.

The sterilized substrate is then cooled to an incubation temperature of 95-115F.

Cultivation This is done using about 2-6% standard yogurt-making starters, such as Lactobacillus bulgaricus and Streptococcus thermophilus, at about 95-115°F, preferably about 2% . Do this for 5-4 hours. Known cultured bacteria, their amounts, and general fermentation conditions can be used. Initially, the pH of the substrate is about 6.5, after completion of fermentation it is about 4.5-4.0, usually about 4.2-4.
It decreases to 4.3 (after about 3.5 hours of fermentation). This pH also decreases slightly during subsequent steps, resulting in a final product with a pH of approximately 3,
8 to 4.1. In fact, the completion of culture is indicated when a predetermined pH is reached.

The additives mentioned in step (d) should be added when the yogurt base is at an elevated temperature, i.e., greater than about 95-100°F, and at least the addition is complete after the mixture has cooled to some extent. However, addition should begin when the yogurt base is at that temperature. However, the addition should be completed at a temperature of about 85F. if,
If addition begins after the yogurt base has cooled below about 95-100 degrees Fahrenheit, it will be difficult to evenly distribute the additive throughout the yogurt base, creating clumps that cannot be removed later and creating a non-uniform appearance. , resulting in an unacceptable final product.

The functions of the additives are as follows.

(1) Carrageenan: This helps prevent protein aggregation, whey separation, and helps obtain a smooth product with sufficient body. Rather, it is a counterproductive additive, as it tends to create lumps that damage the structure of the product.
Avoid using excessive amounts.

(11) Citrate ion: This helps prevent sedimentation reactions during sterilization. That is, it provides a more stable protein dispersion.

It functions as a pH buffer and a sequestering agent for heavy metals. Such citrate ion can be added as a salt, such as sodium citrate, or as an acid, and in the case of an acid, also serves as a pH adjuster if necessary.

(Ill starch: It is a smooth starch with a suitable body,
Helps get a homogeneous product. Due to the effect of the particular processing conditions used, the amount of starch required is relatively small.

-V) Sugars: In the present invention, sugars serve as essential dispersants and sweeteners for other additives such as gums to help prevent protein aggregation. Sugar is present at 3-6% by weight, preferably 4-5% by weight.

As mentioned above, these additives are preferably added in the form of an aqueous slurry. The water content of the slurry is approximately 10-15% of the initial total milk solids content, preferably 15-20%, when the slurry and yogurt-base are mixed.
, typically calculated to be reduced to a predetermined value of about 12-14%, preferably about 13% (wt%).

Simply heating natural yogurt results in virtually complete aggregation of the proteins as the temperature increases. This results in hard, relatively large protein clumps that are practically impossible to convert into smaller particle forms;
The resulting yogurt product has an unacceptable quality or grainy mouthfeel. A very important feature of the present invention is the temperature/time processing step in the process, so that the protein does not impart a grainy texture to the product during the particular homogenization step, and
On the contrary, it is preconditioned in such a way that it can be transformed into small shapes that make the product smooth and creamy.

In this preconditioning step, the protein is denatured and becomes soft.
It is believed that it takes on a curd-like shape and can be transformed into a rough, bland granular form during the mild homogenization process.

Yet another factor to consider is the effect of this heat treatment on the starch. Gelatinization of a significant portion of the starch complicates the subsequent processing of the required proteins. According to the invention, this necessary protein preconditioning can be carried out in two ways after preparation of the yogurt base and additive mixture without significant gelatinization of the starch.

(a) Hold the mixture at 140-155°F for 5-20 minutes and then raise the temperature to <17 u'F as quickly as possible when performing the next one-step homogenization step (f). This operation is generally employed when carrying out the process of the invention batchwise.

(b) The temperature of the mixture is adjusted to the next one-step homogenization step (
When performing f), quickly, within about 60 seconds, about 170
Raise it to 0F. This method is normally employed when carrying out the invention in a continuous manner.

Most conventional homogenization processes using continuous two-stage homogenization methods apply pressures of 1500 to 2 (J Oup psi or more) in the first stage, whereas the method of the present invention uses approximately 1500 J Oup psi or more. A one-step homogenization is performed at a medium or low pressure of ~50 (J psi), preferably about 750-1250 psi, more preferably about IUUOp8i.

The homogenization is carried out at a temperature of at least 140°F, advantageously about 150°F.
Perform at high temperatures from 170°F to 100°F.

As mentioned above, yogurt is a structurally relatively delicate product, and the relatively mild homogenization described above surprisingly results in a slightly increased viscosity and a smooth texture, with no protein particles remaining. A product with a smooth mouthfeel, a non-grainy size, and a dispersed state can be obtained. The standard two-step homogenization operation commonly employed destroys the yogurt product and gives the product a grainy texture.

Sterilization Following homogenization, sterilization is performed by increasing the temperature of the mixture. This is preferably carried out in such a way that the work input to the yoghurt is as low as possible, and tube heat exchangers and scraped surface heat exchangers have been found to be suitable for this purpose.

The temperature is then cooled to below 85°F and the mixture is aseptically filled into sterile retail size containers.

Methods and apparatus for sterilizing such containers and aseptically filling fluids therein are well known and widely used. For example, Dole Aseptic Line M
Odel 4520) 19 manufacturing equipment is suitably used in the process of the present invention.

As is common in the processing of fluid foods, care should be taken to use equipment that eliminates the entrainment of air into the product as much as possible, e.g. mixing equipment, as air entrainment may destabilize the product. , mold growth and other negative effects.

It is not essential to immediately homogenize, sterilize and process the mixture obtained by mixing the yogurt base and the additives. The mixture may be cooled and then subjected to a protein preconditioning step, a homogenization step, etc. However, it is essential that the mixing of the additives with the yogurt base begins at a high temperature above 95F, otherwise it will not be possible to blend these ingredients uniformly throughout the yogurt.

In fact, to obtain pasteurized yoghurt batchwise by the method of the invention, the addition of the additives to the yoghurt base is started at the culture temperature, mixed and the resulting mixture is gradually cooled. The entire mixture is finally cooled to about 40<0>F over 4 hours, and mixing of both components is completed in about 3u to 45 minutes before the temperature drops below about 85<0>F.

Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto.

Example 1 120 Bonds of skimmed milk powder was added to 5700 Bonds of whole milk (3.5% milk solids) warmed to 100° F. with stirring. The milk solids content of the mixture is approximately 17.8%, and the milk fat content is approximately 2
．． It was 6%. The mixture was then homogenized and heated at 190°
Sterilize by heating at F for 10 minutes and cool to 110F. This was inoculated with 1801 pounds of Lactobacillus bulgaricus and Streptococcus thermophilus cultures and mixed. Incubation was performed at 110°F until the initial pH of 6 was reduced to approximately 4.4 (required approximately 4 hours). At this point the temperature was rapidly raised to about 140°F and an aqueous slurry consisting of the following ingredients was added.

Citric acid 6 pounds Carrageenan (1) 8-bond sugar (powdered glucose) 360 pounds Pectin (2
118 pounds starch (3) 72 pounds water
17 Bond (1): Lygomme CD S (Lygomme CD S %Frank
Dempsey & 5ons LtdToront
o ) (2): Pecti 7 P M (A/S K
obenhavnsPectinfabrik) (3): Resister starch (Rezista 5tarch
, 5taleyCO0) The resulting mixture was rapidly (approximately 15 minutes) heated to 160°F. During this time, the protein undergoes preconditioning, i.e., soft
It was modified to the extent that it formed a curd, and the starch remained unchanged. The mixture is then heated at a pressure of 1 oopsi for about 6
Homogenization was carried out in one step for 0 minutes.

The material at this stage was of course plain yogurt based and several similar batches were made using the method described above. The following pureed fruit ε and natural fruit flavor combinations were added to each of these batches.

Strawberry m: Fruit 882.65 Bond, Nartuff
(Narrdan) Strawberry-Plain Natural Flavor 2P-3098122, 12 Bond (
0.3%) Raspberries: 882.65 pounds of fruit, raspberries
Flavor 11.05 Bond (0,15%) Peach: Fruit 882.65 Bond (12%), Peach Flavor 150.1 Bond (2,0%) Orange: Fruit 882.
65 pounds (12%), orange flavor 7.36
Bond (0.1%) The fruit was pureed containing fruit chunks. The combination with natural fruit flavors was mixed with the yogurt and the entire mixture was heated in a heat exchanger at 190-200°F for approximately 5 minutes to complete pasteurization and gelatinization of the starch. Next, desired sterilized plain yogurt 11
The item was cooled to below 80'F and prepared for filling on a sterile filling line. Although the Doll sterile line model 520 was used in this embodiment, the present invention does not have the essential feature of using a specific filling line for the filling method.

Example 2 1.31F (3 pounds) of skimmed milk powder was added to 661 whole milk (3.3% milk solids) heated to 100F with stirring. The resulting mixture had a milk solids content of 13.7N and a milk fat content of 2.2X. Sterilize the mixture by heating it to a temperature above 1900F, cool it to 100-1100F, and add Lactobacillus bulgaricus and Staphylococcus thermophilus cultures to 2% by weight (1,361'f, 3 bonds) of the mixture. Bacteria were mixed. Cultivation was carried out for about 5.5 hours, during which time the initial pH of about 6 decreased to about 4.15. The temperature of the mixture was then increased to 1 over a period of 20-25 minutes.
I raised it to 40-145F and preconditioned the protein. A dry mixture consisting of the following ingredients was then sprinkled thereon.

Citric acid 68.19 (0.1% by weight) Reboom CD8 190.5g (0.28% by weight) Sugar (powdered glucose) 2.38g (3.5% by weight) Pectin JM 204.39 (0.3% by weight ) Register starch 816.69 (1.2%) The resulting mixture was homogenized in one step for 15-20 minutes at a pressure slightly less than 1000 psi. This yielded the desired plain yogurt 68Ky (150 bonds), which was then heated in a heat exchanger at 190°F for 2 minutes to complete pasteurization and gelatinization of the starch to obtain the desired texture. The product was cooled and aseptically filled as in Example 1.

As is clear, if desired, the product can be converted into a fruit-flavored product similar to Example 1.

Example 3 A batch of 96 lbs. of whole milk (3.5% milk solids) was heated to 100'F and, with stirring, 2% skimmed milk powder (970 & 2 lbs.) was added to the mixture. was heated to 190°F for 10 minutes. After sterilization, the mixture was cooled to 110°F and 970 g (2
lbs) were mixed. Incubation continued at 110°F until pi (4-4.5 hours) decreased to 4.25.

Separately, a dry mixture of the following components was prepared.

Citric acid 45.49<0.1% by weight) Ligome CD8 127g (0.28% by weight) Sugar
2043g (4.5% by weight) Pectin JM 136.2g (0.3% by weight) Register starch 544.11 (1.2% by weight) Mixture 130
Warm to 20 °F, sprinkle on cultured substrate, and then
The temperature was raised to 145°F over a period of approximately 1 minute. During this time, preconditioning of the desired protein occurred. 100OP of the whole mixture
Homogenize in one step for about 20 minutes under sI pressure and then sterilize for 2 minutes at 190°F. The product was then cooled to below 80°F while being maintained under sterile conditions before filling the containers.

As mentioned above, the resulting product is a brain yoghurt and can be easily converted into the desired fruit-flavored product as in Example 1.

Claims (1)

Claims: (11) holding the sterilized substrate at an elevated temperature for a sufficient period of time to sterilize it; A yogurt base is obtained by inoculating a yogurt culture that produces lactic acid and incubating the substrate until the pH drops to about 4.5-4.0 at that temperature (di the yogurt base is extremely high). While at temperature, add the following ingredients: carrageenan about 0.1-0.8% citric acid ions about 0.05-0.2% starch
Approximately 0.5-1.5% sugar
about 2.0-6.0% and water if necessary.The milk solids content of the whole mixture is about 10%.
(e) The resulting natural yogurt is subjected to protein preconditioning without substantial gelatinization of the starch. (f) subjecting the mixture to a temperature of up to 170° F. for about 500° C.;
Homogenized in one step under pressure of ~1500 psi, fg
l Optionally add flavor and/or flavor to the homogenized mixture.
or adding a flavoring agent; (h) pasteurizing the resulting mixture at a temperature of at least 170°F; and (i) cooling the pasteurized yogurt to below 85°F. (2) Raise the temperature of the natural yogurt to the homogenization temperature in about 0.5 to 5 minutes without lowering it below the culture temperature, and add the ingredients of step fd) until the temperature of the natural yogurt reaches about 145OF. The manufacturing method of item (1) above, which is completed by. (3) The method according to item (1) above, wherein the temperature of the natural yogurt is raised to about 140-1601, and held at this temperature for 5-20 minutes to pre-condition the protein. (4) In step fdl, the ingredients are added to the yogurt base from an incubation temperature of about 100 to 115 QF to about 85 QF.
The method of paragraph (1) above, in which the temperature is added and mixed while the temperature is reduced to 0.degree. (5) The method of any one of paragraphs (1) to (4) above, wherein in step (d), furthermore, up to 0.5% by weight, based on the natural yogurt, of pectin is added to the yogurt base. (6) Homogenization in step (f) at about 800-1200 psi
Any one of the above items (1) to (4) performed in 05
Manufacturing method. (7) The method according to any one of items (1) to (4) above, wherein in step 1d), about 0.2 to 0.5% carrageenan is added. (8) In step (d), about 0. Ll 75-0. (
The manufacturing method according to any one of the above items (1) to (4), in which citrate ions of J5X are added. (9) The method according to any one of items (1) to (4) above, in which about 0.75 to 1.25% of starch is added in step 1d). The manufacturing method according to any one of the above items (1) to (4), in which about 4 to 5% of sugar is added in (1ω step fd). (111 step fb) culture temperature is approximately 108-112°F
The manufacturing method according to any one of the above items (1) to (4). a2 process value), the milk substrate is sterilized at approximately 190 to 210
The manufacturing method according to any one of items (1) to (4) above, which is carried out by heating at temperature 1 for up to about 30 minutes. 03 The manufacturing method according to any one of the above items (1) to (4), in which the component is added as an aqueous slurry in step (d). (141 The production method according to any one of the above items (1) to (4), wherein the total milk solids content of the milk substrate is 17 to 19% by weight.