Technically, it’s not “beer” until we add hops – so a better question is, what is wort, and why do we boil it during the brewing process?

Wort is the sugary liquid we’re left with after we mash grain to turn starch from grains into fermentable sugars.

Boiling wort is just as important as any other step in the brewing process. A boil that isn’t strong enough, or isn’t long enough, can lead to some serious off-flavors in your beer. There are 6 main reasons we boil…

1. Sterilization

There’s tons of stuff that can be found in grain, hops, and other adjuncts that we don’t want in our beer. Boiling wort gets rid of any microorganisms we don’t want making it’s way into the finished product.

2. Hop Additions

Bittering - The addition of hops into the boil kettle is two-fold. Hops added during the boil will have their alpha acids isomerized, which contributes to overall bitterness in beer. These hops, often referred to as your “bittering addition”, are typically added at the start of a boil and don’t offer much for aroma and flavor - only bitterness.

Aroma & Flavor - On the other hand, hops added towards the middle or end of a boil, or at flameout or whirlpool (when the beer is done boiling), contribute greatly to the aroma and flavor of a beer. Alpha acids in the hops don’t have as much time to isomerize and therefore contribute less to bitterness and more to flavor and aroma.

3. Concentrate Wort To Desired Gravity

With any given beer recipe, we are targeting a certain gravity (concentration of sugar in the wort). This will ensure when we want to brew a 5% beer, we don’t get a 2% or 8% beer. Boiling evaporates some of the water in the wort and concentrates the sugars so we hit our desired gravity.

4. Drive Away Off-Flavors

Put your lab coat on – things are about to get science-y! During germination, barley produces SMM (S-methylmethionine), and lighter grains (which make up the majority of beer) contain a lot of SMM. When you boil wort, SMM converts to DMS (Dimethyl sulfide), which if not properly boiled off, can cause a beer to smell like canned vegetables and creamed corn – gross!

5. Coagulate Proteins

Boiling wort helps coagulate proteins by denaturing them, which makes them unfold and interact with each other. These proteins will precipitate and settle to the bottom of the kettle where they can be removed during whirlpool (when we literally whirlpool the beer to remove solids from it), leading to clearer wort and better flavor stability.

6. Stop Enzymatic Activity

By stopping the conversion of starches into sugar, you ensure you won’t create any extra fermentable sugars in your wort and end up with a beer that is over your target ABV!