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Boiling Wort


Brew kettles boil wort before fermented into beer at the Weihenstephan brewery on November 16, 2009 in Freising, Germany.
Miguel Villagran/Getty Images News/Getty Images
Homebrewers don’t usually give a lot of thought to the boil. Other than adding hops from time to time there doesn’t really appear to be much happening. But the boil is essential to a good beer for a number of reasons. Besides accommodating the hops schedule the boil also sterilizes the wort, denatures the enzymes that were active in the mash, and stabilizes the proteins. Knowing what happens in the boil and how to manage it will give you more control over your brewing process. Better control means more consistent brews and a greater ability to experiment.


Hops are very important to beer. They contribute a significant amount of the aroma of most styles as well as some flavor. Their oils add a bittering quality to the beer which is important to balance the sweetness of the malt. Without hops, most beers would be cloyingly sweet and virtually undrinkable. Hop oils also contribute a preservative quality to the beer.

If you’re brewing from a recipe, it’s likely that the hops schedule was included. Most schedules require you to add some hops near the beginning of the boil, some more somewhere in the middle and the rest during the last five minutes. These schedules are based on that fact that as hops break down during the boil, the more delicate aspects of them – color and flavor – evaporate or precipitate away. Conversely, the longer they are in the boil, the more of their bittering qualities are released and absorbed into the wort. Thus, the more hops that go in early in the boil, the more bitter your beer will be. The more hops that go in towards the end of the boil the hoppier your beer will seem in aroma and flavor though not necessarily in bitterness.

So, how bitter should your beer be and how do you determine bitterness? The bitterness of a beer is measured with International Bittering Units or IBU. Of course some beers will require more bittering and, since this is your beer, the amount of bittering should be based on your taste. The approximate IBU of your final beer can be determined by dividing (Gallons X 1.34) by (Oz. of hops X % alpha acid X minutes in boil/2). This formula only works up to 60 minutes; after that use 30 instead of "minutes in boil/2." Most hops come with the alpha acid printed on the packaging.

Boiling Extracts

If you’re brewing an extract beer you face a unique challenge. Extract beers can be boiled with only a fraction of the water but this can lead to scorching of the sugars. Scorched sugars are unfermentable so the beer will be sweeter and have less alcohol than intended after fermentation. It will also produce a much darker beer. Boiling with all of the water is the best way to prevent this but with some care you can create successful beers with only three or four gallons in the boil for a five gallon batch.

To avoid scorching, bring your water to a boil first. Then remove the kettle from the heat and stir in the extract syrup. Keep stirring until it is fully dissolved. Return the kettle to the heat and maintain as vigorous a boil as you can so no sugars will settle to the bottom of the pot where they can scorch.

Hot Break

Wort that comes straight from the mash contains, among other things, a lot of different proteins. One of the most important functions of the boil is to remove some of these proteins which can cause side affects ranging from chill haze to off-flavors making the beer undrinkable. It is important to boil any beer for at least one hour and to maintain a rolling boil for that whole time to completely stabilize the brew. Of course you would never want to remove all of the proteins from a beer as they are responsible for some of its most important aspects including color and mouthfeel.

Hops play an important roll in the process of removing these harmful proteins. The malt proteins will stick to the polyphenols from the hops. A vigorous boil assures that these polyphenols will actively move about in the kettle and gather as many of the proteins as possible. As these unstable proteins gather, or flocculate, they form little clouds in the brew. These clouds will fall under their own weight or precipitate to the bottom of the kettle at the end of the boil. This is known as the hot break. This is the most important part of the boil as it removes the nastiest of the potentially harmful proteins – those that can cause off-flavors and instability. You can judge when the hot break occurs by taking a sample of wort. You will see the cloud or flocks of protein suspended in the sample. Once removed from the agitation of the boil, these clouds will settle to the bottom of the container. When this happens you will know that you’ve achieved the hot break.

pH Levels

The ph level of the boil is important to create an efficient break. Levels of 5.0 - 5.5 should be maintained to fully precipitate the bad proteins out of the wort. You can use acid or calcium carbonate to regulate the ph level. The ph will drop during the boil but only .2 or .3 so once you’ve hit the target range you really don’t need to monitor it closely unless you accidentally drop an orange in your brew kettle.

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