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Yogurt is a fermented milk product that contains the characteristic bacterial cultures Lactobacillus bulgaricus and Streptococcus thermophilus. All yogurt must contain at least 8.25% solids not fat. Full fat yogurt must contain not less than 3.25% milk fat, low fat yogurt not more than 2% milk fat, and nonfat yogurt less than 0.5% milk.
The two styles of yogurt commonly found in the grocery store are set type yogurt and swiss style yogurt. Set type yogurt is when the yogurt is packaged with the fruit on the bottom of the cup and the yogurt on top. Swiss style yogurt is when the fruit is blended into the yogurt prior to packaging.
Ingredients
The main ingredient in yogurt is milk. The type of milk used depends on the type of yogurt – whole milk for full fat yogurt, low fat milk for low fat yogurt, and skim milk for nonfat yogurt. Other dairy ingredients are allowed in yogurt to adjust the composition, such as cream to adjust the fat content, and nonfat dry milk to adjust the solids content. The solids content of yogurt is often adjusted above the 8.25% minimum to provide a better body and texture to the finished yogurt.
Stabilizers may also be used in yogurt to improve the body and texture by increasing firmness, preventing separation of the whey (syneresis), and helping to keep the fruit uniformly mixed in the yogurt. Stabilizers used in yogurt are alginates (carageenan), gelatins, gums (locust bean, guar), pectins, and starch.
Sweeteners, flavors and fruit preparations are used in yogurt to provide variety to the consumer.
Bacterial Cultures
The main (starter) cultures in yogurt are Lactobacillus bulgaricus and Streptococcus thermophilus. The function of the starter cultures is to ferment lactose (milk sugar) to produce lactic acid. The increase in lactic acid decreases pH and causes the milk to clot, or form the soft gel that is characteristic of yogurt. The fermentation of lactose also produces the flavor compounds that are characteristic of yogurt. Lactobacillus bulgaricus and Streptococcus thermophilus are the only 2 cultures required by law (CFR) to be present in yogurt.
Other bacterial cultures, such as Lactobacillus acidophilus, Lactobacillus subsp. casei, and Bifido-bacteria may be added to yogurt as probiotic cultures. Probiotic cultures benefit human health by improving lactose digestion, gastrointestinal function, and stimulating the immune system.
General Manufacturing Procedure
The following flow chart and discussion provide a general outline of the steps required for making yogurt.
General Yogurt Processing Steps:
1.Adjust Milk Composition & Blend Ingredients
2.Pasteurize Milk
3.Homogenize
4.Cool Milk
5.Inoculate with Starter Cultures
6.Hold
7.Cool
8.Add Flavors & Fruit
9.Package
1. Adjust Milk Composition & Blend Ingredients
Milk composition may be adjusted to achieve the desired fat and solids content. Often dry milk is added to increase the amount of whey protein to provide a desirable texture. Ingredients such as stabilizers are added at this time.
2. Pasteurize Milk
The milk mixture is pasteurized at 185°F (85°C) for 30 minutes or at 203°F (95°C) for 10 minutes. A high heat treatment is used to denature the whey (serum) proteins. This allows the proteins to form a more stable gel, which prevents separation of the water during storage. The high heat treatment also further reduces the number of spoilage organisms in the milk to provide a better environment for the starter cultures to grow. Yogurt is pasteurized before the starter cultures are added to ensure that the cultures remain active in the yogurt after fermentation to act as probiotics; if the yogurt is pasteurized after fermentation the cultures will be inactivated.
3. Homogenize
The blend is homogenized (2000 to 2500 psi) to mix all ingredients thoroughly and improve yogurt consistency.
4. Cool Milk
The milk is cooled to 108°F (42°C) to bring the yogurt to the ideal growth temperature for the starter culture.
5. Inoculate with Starter Cultures
The starter cultures are mixed into the cooled milk.
6. Hold
The milk is held at 108°F (42°C) until a pH 4.5 is reached. This allows the fermentation to progress to form a soft gel and the characteristic flavor of yogurt. This process can take several hours.
7. Cool
The yogurt is cooled to 7°C to stop the fermentation process.
8. Add Fruit & Flavors
Fruit and flavors are added at different steps depending on the type of yogurt. For set style yogurt the fruit is added in the bottom of the cup and then the inoculated yogurt is poured on top and the yogurt is fermented in the cup. For swiss style yogurt the fruit is blended with the fermented, cooled yogurt prior to packaging.
9. Package
The yogurt is pumped from the fermentation vat and packaged as desired.
Yogurt Nutrition
Yogurt nutrition varies widely depending on the type. Yogurt made from skim milk is considered fat free. Yogurt made from whole milk is full fat.
One cup of plain, low-fat yogurt contains:
Calories: 154
Fat: 3.8 grams (g)
Protein: 12.9 g
Total sugars: 17.2 g
Calcium: 448 milligrams (mg)
Magnesium: 41.6 mg
Phosphorus: 353 mg
Potassium: 573 mg
Sodium: 172 mg
Folate: 27 micrograms (mcg)
Vitamin B12: 1.37 mcg
Yogurt Types
The different types of yogurt are made from different types of milk. They may also vary in how they are prepared.
Low Fat or Non-fat
Low-fat and nonfat yogurt are made from 2% (low-fat) and skim (nonfat) milk, respectively. Adding bacterial culture to milk thickens the mixture and adds a tangy taste. Most types of low-fat or nonfat yogurt have a smooth, creamy texture.
Kefir
Kefir is a fermented yogurt drink with a thinner texture than traditional yogurt. It has a longer fermentation process, with grains blended into it. It has a tart taste and may feel a bit bubbly.
Greek Yogurt
Greek yogurt is strained to remove liquid and whey (a type of protein found in dairy). It has a thicker consistency than other types of yogurt. It is also richer in protein and has a more tangy taste. One serving of Greek yogurt contains 20 g of protein.
Reference
Name:- Mansi Shakyawar (M.Sc. 2nd Sem)
Roll no:- 13
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