How is yoghurt made?

Yoghurt has been around for thousands of years and has been an integral part of many cultures. Although yoghurt and curd may be quite similar but they have very subtle differences. The starter culture of curd is only lactobacillus family of bacteria while for making yoghurt, Steptococcus thermophilus bacteria is used along with Lactobacillus. Yoghurt generally has considerably higher amounts of gut friendly bacteria as compared to curd, making it a better probiotic option.


Types:

There are 5 main factors which dictate the diversity of yoghurt:

  1. Type of milk: cow, goat, sheep, conventional, organic.

  2. Fat content: full fat, low-fat, no-fat.

  3. Texture: set-type, stirred, concentrated, drinking, frozen, powder.

  4. Flavour: plain, sweetened, flavored, added fruits.


Manufacturing:

1) Raw materials:

Starter bacterial culture, milk, sugar, stabilizers, and fruits and flavoring are the basic ingredients used for industrial manufacturing of yoghurt.


2) Modifying milk composition:

To make a firm and stable yoghurt, the solid content of milk is increased either by evaporation or addition of milk powder or concentrated milk while fat is reduced by centrifuging the milk in a device called separator. The final total solid content of milk is around 16% of which 1-5% is fat.


3) Pasteurization:

After modifications, stabilizers are added in milk and pasteurized. Usually starch, pectin and guar gum are used as stabilizers as they have minimal effect on flavours. The manufacturer may also choose not to add any stabilizers to give yoghurt a ‘clean label’. During pasteurization, milk is heated to about 90°C for about 7 minutes. It is primarily done for deactivating pathogens and denaturing proteins which helps in reducing risk of gel syneresis (separation of water from yoghurt). Heat treatment also improves effectiveness of starter cultures by inactivating Lactoperoxidase enzyme which is a natural preservative in milk.


4) Deaeration and Homogenization:

Between pasteurization and homogenization, the oxygen content of yoghurt is reduced by vacuum de-aeration at 70°C which helps shorten fermentation duration. During homogenization, the mixture is passed through either a homogenizer or a viscolizer which break fat globules into smaller particles and evenly disperses them by passing the mixture through small openings under high pressure. Homogenization is a crucial step to ensure smooth and creamy texture of yoghurt.


5) Fermentation:

As mentioned above, the starter culture for yoghurt contains a combination of strains of Lactobacillus and Steptococcus bacteria and the suppliers of these strains have a variety of combinations which help manufactures manipulate the final taste and texture of the product. The mixture is cooled to about 45°C and inoculation is added at about 2% concentration. This temperature is maintained for about 3-4 hours for incubation during which the bacteria break down sugars in milk to form lactic acid, acetaldehyde and exopolysachharides. The acid formed reduces the pH of the mixture and causes protein to coagulate and form a gel and impart a sour taste. Acetaldehyde and exopolysachharides contribute to yoghurt’s characteristic aroma and texture respectively. Level of pH is tested to determine completion of the fermentation.


6) Flavoring and packaging:

Once the desired pH is attained, the yoghurt is rapidly cooled to 4-5°C within 2 hours to arrest further acidification. Flavours, fruits, sweeteners and aroma compounds may be added at this stage. Followed by packaging of the final product in plastic cups.


Health benefits:

  1. Nutrients: yogurt is a good source of minerals and vitamins like calcium, vitamin B, phosphorus, magnesium and potassium.

  2. Protein content: thick types of yoghurt such as greek style have 11 gms of protein per 100 gms. High protein foods help in achieving satiety along with numerous health benefits.

  3. Digestive health: yoghurt is a probiotic food which means it contains gut friendly bacteria which help keep our digestion healthy.

  4. Strengthen immunity: probiotics and trace mineral like magnesium have been shown to reduce inflammation and fight viral diseases.

  5. Prevent osteoporosis: calcium, phosphorus and protein are essential for maintaining bone health.

  6. Promote heart health: studies have shown that whole milk yoghurt may increase HDL cholesterol and lower blood pressure, which helps reduce risks of cardiovascular disease risk.

  7. Weight management: protein along with calcium may increase levels of appetite reducing hormones. Plus, studies on dairy products have shown that consumption of yoghurt may help reduce weight and body fat.



The takeaway box:

Yoghurts are a great source of probiotics, protein, calcium and trace minerals which are important for digestive and bone health and can be a good snacking option, but people who are lactose intolerant and allergic to milk may need to avoid all types of it. Added sugar may be a concern for diabetics and those trying to shed some weight, the best options for them are to go for plain or sugar free options.


References:


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