Processing of set style yoghurt

Yoghurt is mainly of two types i.e. set yoghurt and stirred yoghurt. Set yoghurt (which includes fruit-on-the bottom) is formed in retail pots as lactic acid bacteria ferment lactose into lactic acid giving a continuous gel structure in the consumer container. Yoghurt properties can be enhanced by the addition or treatment with various additives.

In processing, set style yoghurt is incubated and cooled in the final package and is characterized by a firm jelly like texture. Set-style yoghurt is fermented in a retail container, filled after milk inoculation and is incubated in an incubation room at a suitable temperature normally40-43°C for approximately 2:30 to 4 hrs. Yoghurts are directly transferred to a cold store or blast chilled in cooling tunnels.

Fruit and flavors are added at different steps depending on the type of yoghurt. For set style yoghurt the fruit is added in the bottom of the cup and then the inoculated yoghurt is poured on top and the yoghurt is fermented in the cup.

Set-style yoghurt should have smooth consistency without cracks or holes, custard like, semi solid consistency without any surface whey.

Processing of set style yoghurt

Yoghurt processing

The milk use during production depends on the type of yoghurt being made. Whole milk or skimmed milk can be used. Milk chosen for yoghurt manufacturing must be of high bacteriological quality.

All yoghurt processing begins with milk pasteurization. Higher temperature and longer hold times are used for yoghurt production than most other cultured yoghurt. Milk is heat treated to denature milk proteins.

The denatured protein result in a former yoghurt texture and shorter incubation times. It gives a more stable yoghurt as well as eliminating bacteria contaminants and reducing the oxygen content of the milk.

Yoghurt milk heated to 85°C for 20 minutes and incubated for 42° for 3 hours. The incubation may be in stored tanks or in retail containers. In both styles, flavoring can easily be added by a dosing pump immediately before dispensing into the containers used for distribution.

Although unhomogenized milk may be used for yoghurt, most manufacturers homogenize yoghurt mix in order to prevent creaming during the incubation period, to assure uniform distribution of the milk fat, and to stabilize the coagulum against whey separation.

Furthermore, homogenization, followed by high temperatures, improve yoghurt viscosity.

Some yoghurts are made with unhomogenized milk to intentionally provide a cream layer on top of the yoghurt.

Milk is turned into yoghurt using bacteria called Bacillus lactus. Modern industrial processes utilize defined lactic acid bacteria as a starter for yoghurt production.

A starter consists of food grade microorganisms that on culturing in milk predictably produce the attributes that characterized yogurt. These are added to the milk as a bacteria culture.

The bacteria grow and produce lactic acid that thickens the milk and creates the acidic flavor of yoghurt. Fermentation is stopped by immediately cooling the product.

The final product has a pH value of about 4-4.2 and contains 0.7-1.1% of lactic acid. The yogurt is then cooled to 5° C and stored at the temperature.

The majority of yoghurts manufactured in the United States is Swiss-style, or stirred, stabilized with modified food starch, typically from waxy and gelatin.

The popularity of yoghurt has been propelled by the availability of sweetened fruit flavored product.
Yoghurt processing