Converting Starch To Fermentable Sugars: A Beginner’s Guide

Starch to glucose pathway — Science Learning Hub


Converting starch to fermentable sugars is a crucial process in the production of beer, spirits, and other alcoholic beverages. In this article, we’ll explore the basics of this process and how it can be done at home.

What is Starch?

Starch is a complex carbohydrate that is found in many plants such as corn, wheat, and potatoes. It is made up of glucose molecules linked together in a long chain.

Why Convert Starch to Fermentable Sugars?

In order to make alcohol, yeast needs a source of fermentable sugars. Starch is not a fermentable sugar, so it needs to be converted into simpler sugars such as glucose and maltose before it can be fermented.

The Conversion Process

The process of converting starch to fermentable sugars is called mashing. Mashing involves mixing crushed grains with hot water in a vessel called a mash tun. Enzymes in the grains break down the starch into simpler sugars.

Types of Enzymes

There are two main types of enzymes involved in mashing: alpha-amylase and beta-amylase. Alpha-amylase breaks down the starch into longer chains of sugars, while beta-amylase breaks down these longer chains into shorter chains such as maltose.

The Mash Schedule

The mash schedule refers to the temperature and timing of the mashing process. Different temperatures and times will result in different types of sugars being produced. For example, a mash at a lower temperature will produce more fermentable sugars, while a mash at a higher temperature will produce more unfermentable sugars.

The Sparge

Once the mashing process is complete, the liquid containing the converted sugars is drained off into a separate vessel called a boil kettle. The remaining grains are then rinsed with hot water in a process called sparging to extract any remaining sugars.


The liquid in the boil kettle is then boiled for an hour or more. This serves to sterilize the liquid and also adds hops, which give the beer its characteristic bitterness and flavor.


After boiling, the liquid is cooled and transferred to a fermenter. Yeast is then added, and fermentation begins. The yeast consumes the fermentable sugars and produces alcohol as a byproduct.


Converting starch to fermentable sugars is an essential part of the brewing process. By following the steps outlined in this article, you can create your own delicious and unique alcoholic beverages at home.