Extraction rate

The most important part of a grain of wheat is its endosperm, which in its raw state is a gritty off-white substance. When wheat is ground to make flour, the whole of the grain is powdered. This includes the germ and the tough outer shell called the bran. This flour is known as wholemeal because it contains the whole of the grain.

To make 'white' flour that contains very little of the germ and bran, it must be sieved or 'bolted' several times to separate the endosperm. Different types of flour may be produced depending on how many times it is sieved and how much of the germ and bran is removed. Very fine flours intended for baking cakes may be very thoroughly sieved, for example. The amount that a flour has been processed like this is referred to as its extraction rate.

Extraction rate is expressed as a percentage amount of how much of each grain is left in the flour, on average. Slightly confusingly, then, a higher percentage means a lower extraction rate: 100% is no extraction at all, while 70% is a high extraction rate and denotes a white flour.

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

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