The latest and perhaps most unusual spin-off from space exploration is a yoghurt made from the saliva and gut bacteria of Russian cosmonauts - and it is about to become big business.

The yoghurt was originally developed to help space travellers maintain healthy levels of bacteria in their intestines but it is now becoming a commercial venture.

Cosmonauts who spend a long time in space have a problem: space flight is so demanding on their immune systems that harmful bacteria can build up in their intestines, causing digestive problems.

For the past 25 years, microbiologists at the Institute of Biomedical Problems in Moscow have tackled the problem by collecting samples of cosmonauts' gut bacteria and making yoghurt from them.

Fighting infection

Cosmonauts are routinely given yoghurt before blasting off to the space station Mir, and regular supplies were sent up to the station during bouts of infection in 1989 and 1995.

Nadezhda Lizko, head of the yoghurt project, says the cosmonauts have become very fond of the yoghurt - so much so, that the team is now producing it commercially.

Dr Lizko believes the strict medical supervision given to cosmonauts makes them ideal donors of healthy bacteria.

She and her team have now diversified their products to include fruit-flavoured yoghurts, cottage cheese and traditional Russian cheeses.