Most of yoghurt produced in the UK and in US is of the stirred type which is manufactured in bulk before mixing with fruit and packaging.
The amount of solids in the base milk, to a large extent, determines the physical properties of the final yoghurt product.
Most stirred yoghurt are made from milk base low in fat and milk solids and the manufacture of such products is possible in most types of yoghurt plant.
Six major steps of stirred yoghurt manufacturing include:
*Preparation of milk
*Homogenization
Homogenization the milk base 60 – 70° C and 15-20 MPa pressure.
*Heat treatment
Heat to 80-85° C for 30 minutes or 90-95° C up to 5 minutes.
*Fermentation
After fermentation of yoghurt in large vats, the gel is broken by stirring thus forming a viscous non-Newtonian liquid, which is strongly shear-rate thinning.
Stirring is a crucial process which induces considerable changes in the rheological properties of the final product.
*Fruit addition
Stirred yoghurt is normally flavored with fruit purees or juices and consumers studied in the US preferred strawberry and raspberry.
*Packaging
Most yoghurt contains live bacteria so it must be stored chilled at temperature of about 5° C. This gives yoghurt a shelf life of about 14 days.
Stirred yoghurt should have a thick, smooth consistency and be sufficiently viscous to hold the fruit in suspension during the shelf life of the product.
Stirred yoghurt manufacture
