Milk and its processing has evolved a long way from being consumed as liquid milk to processing of milk to various dairy based product. If we are to list, some of the well known product frequently used in almost all household are Curd, Yoghurt, lassi, chach, paneer, dairy sweets etc. Requirement of these processing evolved from the fact, that milk is highly perishable in nature and cannot be stored long, hence processing if milk help in achieving the product shelf life from certain days to months.
Yoghurt, it is fermented dairy product having sort of thick consistency. And as per FDA code of Federal Regulations – “yogurt is a food produced by culturing cream, milk, partially skimmed milk, or skim milk alone or in combination with a bacterial culture that contains the lactic acid–producing bacteria Lactobacillus bulgaricus and Streptococcus thermophilus.”
Being a rich source of protein and calcium, the fermentation process facilitate the absorption of nutrients in our body. The live bacteria in yoghurt promotes the balancing of good and required microflora in stomach hence promoting digestion. Apart from Lactobacillus bulgaricus and Streptococcus thermophilus other bacterial culture such as Lactobacillus acidophilus, Lactobacillus subsp. Casei, and Bifido-bacteria as probiotic culture.
Principle behind Yoghurt making
The bacterial fermentation of milk facilitates the yoghurt manufacturing process. The process starts with bacteria fermenting the present milk sugar of milk into lactic acids. The produced lactic acid brings down the milk pH to range of 4 and this causes the beginning of protein coagulation in milk.
The influential parameters for yoghurt thickness, consistency, texture and taste are
- Starter culture
- Fat content of milk
- Amount if milk solid, protein
Another approach to have thick and set consistency product is to add skimmed milk powder- the catch point being, addition of skim milk powder to cold milk rather than heated milk or instead of firmer yoghurt, stringy natured yoghurt will be observed.
Yoghurt and its type
Natural Yoghurt – When no flavor or sweetener are added to the prepared yoghurt
Flavored– Have added flavor and sweeter that can be natural or artificial sweeteners
Greek Yoghurt – Natural yoghurt goes through straining process to remove whey content. The thick remaining is Greek yoghurt.
Greek Style Yoghurt– Natural Yoghurt when thickened with milk solids and stabilizers rather than straining.
Set Yoghurt– Yoghurt when fermented in final packing material to get set form.
Stirred Yoghurt– After incubation period is over and yoghurt proceeds for filling it is stirred at particular RPM for certain time to cut have stirred yoghurt
Drinking Yoghurt– To increase the fluidity and flavor, milk is added along with desired fruit and fruit syrups.
Frozen Yoghurt– Regular yoghurt is mixed with pasteurized ice cream mix of milk cream and sugar along with other ingredients such as stabilizers and then frozen
Yoghurt Cheese – Also known as “Labna” , which has its whey drained
How is Yoghurt Processed ?
Yoghurt process or commercial manufacturing have following steps involved –
Step-1: Milk Composition
There is desirable characteristic that is required to start with yoghurt processing. As mentioned, the texture and end consistency depend upon milk composition and to be specific – milk solids. To increase the protein content, skim milk powder is also added in cold milk which enhances the texture.
Step-2: Pasteurization and
The pasteurization step is to kill pathogenic microorganism from milk so that the processed product is free of any form of contamination The process can be either batch pasteurization or continuous pasteurization depending upon the facility. Pasteurization is done at temperature range of 90-95 Deg. C with holding time of 10 minutes.
Along with pasteurization, the milk is homogenized where the fat globules are uniformly broken in to smaller consistent product.
Milk is cooled down to temperature of 42+2 Deg. C, which is to provide most suitable growth temperature to bacteria.
Milk is inoculated with the fermentation culture to a concentration range of 1.5-2% and the temperature of milk is maintained at 42+2 Deg. C for 4-6 hours, depending upon the time required to attain the lower pH of 4
Step-6: Addition of flavors/fruits and other ingredients
Flavors are added to product after cooling. Reducing the temperature stops the fermentation process, hence reduces the change or acidity change.
Flavor addition is also dependent on the type of final product required- In case of set curd, fruits are added at the bottom of the packing cup and then filled with product, while it can also be blended with product during/after fermentation process and then cooled for packing.
Nutritional Chart of Yoghurt
Yoghurt with abundant nutritive value is currently under extensive studies, to unveil many other health benefits of taking yoghurt in diet apart form already known benefits such as acting as immunity booster, reducing chances of infection and reducing risk of colon cancers.
To make it more attractive and to satiate the demand of consumers, research works are going on for new flavor developments, along with increasing nutritional content and increasing the shelf life of yogurt.
- Dairy Council of California. 2015. Yogurt Nutrition. Dairy Council of California