How is bread made with microorganisms

As the bacteria grow they use the milk sugar lactose as an energy source and produce lactic acid. Initially S. L bulgaricus , which is more acid tolerant, continues to ferment the remaining lactose. During this process the pH drops from 6. This inhibits the growth of spoilage microbes. Consequently yoghurt keeps well in the fridge for some days.

The presence of lactic acid causes the structure of the milk protein to change, giving yoghurt its special thickened texture. The lactic acid also gives the yoghurt its sharp taste. Other fermentation products such as acetaldehyde give the yoghurt its characteristic smell. Fruit and flavourings can then be added and the yoghurt packaged in the familiar pots. Microorganisms Microorganisms are very tiny organisms that can only be seen in detail using a microscope.

Examples of microorganisms include: bacteria yeast a type of fungus Microorganisms can be used by humans to produce foods and other useful substances. Using yeast to make bread and beer Yeast is a single celled, microscopic fungus that uses sugar as food. If thermostatically controlled water baths are not available then large beakers of water maintained at the three temperatures can be used. The water temperature in each beaker needs to be monitored using a thermometer, and access to a supply of hot water, eg from a kettle, is needed to top up the beaker as the temperature falls.

The yeast suspension is made by stirring 7 g of dried yeast with cm 3 of warm water. If fresh yeast is used it should not have been kept too long. Fresh yeast can be kept in the freezer for up to two months. Procedure Add 25 g of flour to a beaker and then add 1 g of sugar.

Show Fullscreen Source: Royal Society of Chemistry Make a paste from the flour, sugar and yeast suspension and pour it into a measuring cylinder. Additional information This is a resource from the Practical Chemistry project , developed by the Nuffield Foundation and the Royal Society of Chemistry. Level years years. Use Practical experiments. Category Biological chemistry Food. You can see 4, year-old samples of unleavened bread in the British Museum.

Picture 1. How is it produced? Bread is made from cereal grains ground into flour. Leavened bread is softer due to the action of yeast, which is a fungus. Yeast Saccharomyces cerevisiae contributes both to the texture and flavour of bread.

A dough is made by mixing yeast with flour, salt and water. The yeast ferments sugars in the mixture to make alcohol and bubbles of carbon dioxide.