Bio 3 - Microbiology - Food production using bacteria

People began to domesticate animals quite early in history. They soon realised that the milk that female animals amde for their babies could be used as food for us too

However there is one drawback in using milk as part of the diet: it rapidly goes off, starts to smell and tastes disgusting. However it didn't take people very long to find ways of changing the milk into foods which lasted much longer than the milk itself. These changes depended on the action of microorganisms.

Yoghurt has long been a staple part of the diet in the Middle East but has only become popular in the UK recently. Cheese on the other hand, has been around for a very long time all over the world.

Traditionally, yoghurt is fermented whole milk, but now we can make it from Semi-Skimmed, skimmed and even soya milk. Yoghurt is formed by the action of bacteria on the lactose in the milk. The fermentation of milk produces lactic acid, which causes the milk to clot, making it a lot thicker than milk.

Like yoghurt making, cheese making depends on the reactions of bacteria with milk. These change the texture and taste, and also preserve the milk. Cheese making is very successful at preserving milk, and some cheeses can survive years without decaying.

Just as in yoghurt making, you add a starter culture of bacteria to warm milk. The difference is in the type of bacteria added. The bacteria added in cheese making also converts lactose into lactic acid, but they much more of it. As a result the solid part (curds) are much more solid than the yoghurt ones

Enzymes are also added to increase the seperation of the milk. When its completely curdled you can seperate the curds from the liquid whey. Then you can use the curds for cheese making.

Next you cut and mix the curds with salt along with other bacteria or moulds before you press them and leave them to dry out. The bacteria and moulds which you add are very important, they affect the development of the final flavour and texture of the cheese as it ripens. The ripening can take months or years depending on the cheese.