7 Reasons For Boiling A Wort

Have you ever wondered what was the reason for boiling a wort?
The boil is an aspect of homebrewing that can be taken for granted as a step simply for throwing in the hops, but there are actually several reason for boiling a wort:

• To sterilize the wort
• To stop the enzymatic activity of the mash
• To concentrate the wort
• To boil off unpleasant aroma compounds
• To coagulate proteins so they will drop out
• To extract bitterness from the hops
• To adjust wort color and flavor

All these reasons play a significant part in the final outcome of the beer. It’s color, bitterness, flavor, intensity, over all character are partially a factor of the boil. Let’s briefly cover each reason for boiling a wort.

1. To sterilize the wort
   As homebrewers, we want as much control over our beer as possible. Beer yeast is (usually) the only thing we want growing in our beer. Boiling the wort kills off any microorganisms that may be in the wort or other ingredients. Sterilization requires a minimum of about 20 minutes of boiling.

2. To stop enzymatic activity
   A brewer can control the ratio of fermentable and unfermentable sugars, mouthfeel, and other factors by their command over the mash. Changes in temperature and pH can make a big difference in the enzymatic activity during the mashing process. By heating the wort to a boil, the enzymes in the mash stop their activity and the mix of sugars in the mash is fixed.

3. To concentrate the wort 
   The wort collected after the mash is never the brewer’s intended original gravity. By boiling the wort and knowing one’s boil-off rate, a brewer can execute a precise original gravity for their beer. In many cases a 60-minute boil is sufficient for reaching a desired gravity, but sometimes a longer boil will be required.

4. To boil off unpleasant aroma compounds
   Dimethyl sulfides, commonly referred to as DMS, are compounds produced while boiling a wort and their presence in beer is considered a fault. You might recognize DMS as an aroma similar to cooked vegetables. One of the major reasons for boiling a wort is to get rid of these offensive compounds. A long, vigorous boil will vaporize the DMS. For this reason it’s important to boil the wort uncovered. Aldehydes can also be boiled off.

5. To coagulate proteins
   There are a number of materials in malt, particularly protein, that are suspended in wort. The boil helps these proteins coagulate into larger chunks, which form during the hot break and will settle out during the cold break. Irish moss can aid in this process.

6. To extract bitterness from hops 
   The part of hops that are responsible for bitterness are called alpha acids. In order to contribute bitterness to beer, these alpha acids must be isomerized (a change in chemical structure), which only happens during boiling of the wort.

7. To adjust wort color and flavor
   In some cases, boiling wort can help achieve a darker color and a rich, caramel flavor in the wort. The chemical process responsible for these changes is called the Maillard reaction.

So there they are, 7 reasons for boiling a wort. Can you think of any other reasons we boil wort? Please share them with us!
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David Ackley is a beer writer, brewer, and self-described “craft beer crusader.” He holds a General Certificate in Brewing from the Institute of Brewing and Distilling and is founder and editor of the Local Beer Blog.