Amylase, falling number and why bakers add malt to flour

This is written to be used rather than admired. Each section below is a decision about enzyme activity in flour, and each one has a default.

Why yeast needs help

Yeast cannot metabolise starch directly; it needs simple sugars such as glucose, maltose and fructose. Flour contains only a small amount of free sugar, typically well under two per cent of its weight. Amylase enzymes in the flour break starch chains into maltose, providing a continuing supply during fermentation.

Without adequate amylase activity, a lean dough runs out of food and fermentation slows to a halt. This is why long fermentations depend on enzyme activity as much as on the yeast itself.

Two kinds of amylase

Beta-amylase clips maltose units from the ends of starch chains and is abundant in most flour. Alpha-amylase cuts chains internally, creating many new ends for beta-amylase to work on, and is often in short supply. Alpha-amylase levels depend heavily on whether the grain began sprouting before harvest.

Weather at harvest therefore affects flour behaviour, which is one reason bread flour varies between seasons. Millers correct the shortfall by adding malted barley flour, which is rich in alpha-amylase.

Falling number

The falling number test measures how quickly a stirrer sinks through a heated flour and water paste. High enzyme activity breaks down the starch gel fast, so the stirrer falls quickly and the number is low.

Low activity leaves a thick gel and a high number, indicating flour that will produce a pale, poorly fermenting loaf. Millers blend and supplement to land within a target range, commonly cited around 250 to 300 seconds for bread flour. Home bakers never see this number, but it explains why commercial flour is more consistent than it has any right to be.

Too much enzyme activity

Sprouted grain and some rye flours have very high alpha-amylase, which breaks down starch faster than it can set. The result is a sticky, gummy crumb that never firms properly however long it bakes.

This is a particular problem in rye, which is why rye breads are traditionally acidified with sourdough. Acidity inhibits amylase, so a sour rye dough controls the enzyme activity that would otherwise ruin the crumb.

That is a genuine functional reason for sourdough rather than a flavour preference.

Adding malt yourself

Diastatic malt is malted grain that retains active enzymes, and a small amount boosts a sluggish flour. Typical additions are very small, often well under one per cent of the flour weight, because a little goes a long way. Non-diastatic malt has been heated to destroy the enzymes and is used purely for flavour and colour.

By the second rise, overdosing diastatic malt gives a sticky crumb and a very dark crust, so it is a case where more is clearly worse. Most modern white bread flour is already malted, so additional malt is often unnecessary.

Flour absorbs water differently by brand and by season; hydration is a target, not a rule.

Reading the symptoms

A lean loaf that bakes pale despite a hot oven and a long bake may simply have run out of sugar. A dough that ferments enthusiastically for two hours then stops is showing the same shortage. A sticky, gummy crumb with normal internal temperature suggests too much enzyme activity rather than underbaking.

In the tin, switching flour brands is the fastest diagnostic, since it changes the enzyme profile completely. These are uncommon problems with good commercial flour but they do appear, particularly with home-milled grain.

The takeaway

Flour is a biologically active ingredient, and pale sluggish loaves are sometimes its fault rather than yours.

Temperature and time are the same argument held at opposite ends.