Fermented milk products have been known for centuries. Such products include sour cream, buttermilk, kefir, koumis and various cheeses.
Yoghurt is a fermented milk product which has been known for over a thousand years. The product is believed to have originated in Asia where Turkish nomads were producing material referred to as "yoghurt" by the 8th century AD.
While the nutritive value of yoghurt is primarily determined by the milk from which it is made, yoghurt has the advantage that it is more easily digested than milk. Furthermore, yoghurt has therapeutic value and is used in treatment of intestinal disorders, liver and bile disorders and in the topical treatment of skin and oral disorders.
Yoghurt is therefore a product with considerable market appeal and processes are available for large scale production. However, there is also interest in home production of yoghurt, particularly when a product not available commercially is desired.
In home production, the usual process followed is to precook milk, cool to an incubation temperature, and add a yoghurt culture. Generally, a fresh yoghurt culture is used with each batch of milk.
Yoghurt cultures are known which comprise micro-organisms aggregated with an inert material. Such cultures can be used to prepare yoghurt from a first batch of milk then transferred to a second batch of milk for conversion to yoghurt followed by a further transfer and so on.
A portion of yoghurt produced from a first batch of milk can also be used as a starter culture for a second batch of milk. Further transfers can be made but eventually portions will become ineffectual as starter cultures.
Home production of yoghurt may be facilitated by using a process which includes the step of transferring an aggregated starter culture or portion of yoghurt to additional batches of milk. However, devices or systems for facilitating such transfers are not known.