21.01.2017

Pasteurised/UHT/long life/heat shock yoghurt

Global Bilgiler  /  at  22:06  /  No comments

Depending on the standard of hygiene observed during the manufacture of yoghurt and the microbiological quality of the ingredients and packaging materials, the shelf life of yoghurt is around 3–4 weeks under refrigerated conditions. Various techniques have been used in order to improve the keeping quality of yoghurt, such as:
• freezing and drying
• gas flushing (discussed under separate
• addition of preservatives  headings elsewhere)
• use of aseptic equipment
• application of multiple frequency microwaves
• sterilisation by heat and each of these approaches has its adherents.
A post-production heat treatment helps to prolong the shelf life of the product, since the application of heat inactivates the starter culture bacteria and their enzymes, as well as other contaminants, for example yeasts and moulds. Traditionally, yoghurt was heated for a few hours over low fires of a special type of wood.
The end product was referred to as smoked yoghurt (see Fig. 1.2) and it was preserved over the winter months by placing in jars and covering with either olive oil or tallow. However, in a mechanised plant, the time–temperature Relationships  which are used to achieve the desired effect of pasteurisation are similar to those used for liquid milk processing, although in general a lower energy input is required for yoghurt since the level of acidity is much higher than in milk (Gavin, 1966; Puhan, 1979; Driessen, 1984).

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