Enzymes are molecules produced by living cells that speed up or catalyse chemical reactions. Without enzymes, nearly all the chemical reactions that occur in living things would take place so slowly that the nature of life on Earth would be very different.

There are many different types of enzymes, all of which act upon specific molecules. The particular molecule that a given enzyme acts upon is called its substrate. Enzymes work by breaking down their substrate molecules into different, smaller molecules. Various enzymes are important in breadmaking, where they are responsible for converting the starch in flour into sugars that the yeast can metabolise.

Want to find out more? Look at the chapter on ingredients in the book flour and water.

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