Brew Day Hour 3: The Hop Boil

Brew Day Hour 3: The Hop Boil

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Emma Christensen
May 14, 2015
(Image credit: Melissa Ryan)
(Image credit: Henry Chen)
  • Today's topic: Detailed look at boiling the wort and adding hops.
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By this point in the brew day, we have finished making the base of our beer — the sugary wort — and now it's time to introduce some other flavors. This happens in the form of those tiny, very aromatic, rather pungent hop pellets. Hops, meet beer. Beer, meet hops. Brewers, let's get these two friends better acquainted.

(Image credit: Melissa Ryan)

Talk Like a Brewer

  • The hop boil, or the boil: The period, usually 60 minutes, during which the wort is boiled and hops are added.
  • Hot break: The moment right when the wort comes to a boil and the bubbling wort breaks through the layer of foam that has collected on the surface of the liquid.
  • Hop additions, or hop schedule: The timeline for adding specific amounts of hops to the wort; usually hops are added in doses at the beginning, middle, and very end of the boil.
  • Flame out: The moment when the pot of boiling wort is removed from the heat. Sometimes recipes instruct adding a specific dose of hops at this point.
(Image credit: Henry Chen)

What Happens During This Hour?

Once you're finished sparging, put the pot with the wort back on the stove and crank up the heat. The hop boil begins as soon as the wort comes to a full, rolling boil. A 60-minute boil is typical for most beers, and hops are generally added at the beginning, after 40 minutes, and at the very end (though some beer recipes will vary). I also like to add Irish moss or another clarifying agent along with the second addition of hops; this ingredient helps reduce haziness in finished beers.

One thing to watch out for: the hot break. As the wort starts to heat up and near a full boil, thick creamy-colored foam will start to collect on top of the liquid. Watch for big bubbles of boiling wort to start breaking through the foam — your cue that you can start adding hops.

Also, if your pot is on the smallish side (smaller than 12 quarts), the wort can easily boil over at this point. Keep an eagle eye on the pot, and if it looks like it might boil over, quickly reduce the heat or remove the pot from heat until the foaming subsides. You can also try stirring the wort continuously or squirting water on the foam. Once the boiling wort has broken through and most of the foam has dissolved, the risk of boil-overs is much lower.

Pellet hops and whole leaf hops
(Image credit: Melissa Ryan)

Why Is the Hop Boil Important?

The resins in the hops, which give our beer some bitterness, need this boiling time to be fully absorbed into the wort. During this hour, the wort also becomes sterilized, which gets rid of any bacteria or wild yeast and guarantees that the only thing that will take up residence in our beer is the yeast that we add ourselves.

Measure your hops before adding them to the wort, preferably with a digital kitchen scale. Beer recipes use very calculated amounts of hops to give the beer very specific degrees of bitterness and flavor. It can be fun to tinker with these amounts once you gain a little experience, but when you first start out, it's best to stick with what the recipe says. When you're measuring very small amounts, like just a few grams, it can sometimes be easier and more accurate to weigh double the amount needed, then visually split the pile of hops in half to get what you need.

Leave the pot uncovered during the entire hop boil. There are a few compounds that need to evaporate during the boil; if they remain in the beer (or re-condense because you covered the pot) these compounds can leave some unsavory flavors in the finished beer. You'll generally lose 1/2 gallon of liquid to evaporation over an hour-long boil, and beer recipes are designed to account for this.

Even if you don't want to add hops to your beer, I still recommend boiling the wort at least briefly in order to sterilize it and allow some of those unwelcome compounds to evaporate.

(Image credit: Melissa Ryan)

What to Do: The Hop Boil

These general directions apply to any batch of beer you brew. Your specific recipe will tell you the exact length of the boil, amounts and types of hops, and when to add them to the boiling wort.

Flip through the slideshow above for step-by-step photographs of each step of the hop boil.

  1. Bring the wort to a boil: Transfer the pot with the wort to the stove and bring to a full, rolling boil over high heat.
  2. Measure the hops: While you're waiting for the wort to boil, measure out the hops and the Irish moss (if using), and keep them near the stove.
  3. Watch for the hot break: As the wort comes to a boil, creamy foam will collect on the surface. If your pot is a bit small (less than 3 gallons), keep a close eye on the wort so it doesn't boil over at this point (see Troubleshooting, below). Once the wort bubbles up through the foam and the foam starts dissolving back into the wort (the hot break), you can start adding hops.
  4. Begin adding hops: Hops are generally added in three additions — bittering hops at the very beginning of the boil, flavoring hops after 30 to 40 minutes, and aroma hops at the very end. Check your recipe for exactly when to add each addition of hops. You don't need to stir the wort to dissolve the hops; they will dissolve on their own.
  5. Boil for 60 minutes (or as specified in your recipe): Continue adding hops according to the instructions in your recipe. During the hop boil, keep the wort at a full, rolling boil, and leave the pot uncovered.
  6. Remove the pot from heat: As soon as the boil ends, remove the pot from heat and begin cooling the wort (which we'll talk about in the next lesson).
(Image credit: Melissa Ryan)

Troubleshooting the Hop Boil

My wort is about to boil over — help!

If your pot is on the smallish side (smaller than 12 quarts), the wort can easily foam up and boil over the side of the pot as it nears a full boil. Keep an eagle eye on the pot, and if it looks like it might boil over, quickly reduce the heat or remove the pot from heat until the foaming subsides. You can also try stirring the wort continuously or squirting water on the foam. Once the boiling wort has broken through and most of the foam has dissolved, the risk of boil-overs is much lower.

Oops, my wort boiled over — is my beer OK?

Boil-overs are a rite of homebrewing passage — welcome to the club! Just clean up the spill and carry on with the hop boil. You might end up with a little less wort at the end, but it's fine to top it off with water.

I forgot to add hops when the recipe said to.

Add the hops as soon as you remember. You might notice less bitterness or hop flavor than you expected, but the beer will still ferment just fine.

I miscalculated and added too much hops.

You will end up with a stronger hop bitterness and hop flavor in your finished beer — just call it an IPA and no one will be the wiser.

I miscalculated and didn't add enough hops.

Add the extra hops as soon as you realize the mistake, but otherwise don't worry. You may end up with less hop bitterness and hop flavor in your finished beer — just call it an amber or a pale ale and no one will be the wiser.

I just noticed that there is a different alpha acid percent (AA%) on my package of hops than in the recipe.

If it's off by just a percent or so, don't worry about it. If it's off by more than that, follow these steps to recalculate the amount of hops that you need:

  1. Multiply the AA% of the recipe's hop by the number of grams called for in the recipe.
  2. Divide that number by the AA% of your hop, and you'll have the grams you need of your new hop.

In mathematical terms: (AA% recipe hop x grams recipe hop)/AA% new hop = grams new hop

You can also use this formula if you want to substitute one kind of hop for another kind of hop in a recipe, but don't want to change the overall bitterness.

I forgot about the beer on the stove and let it boil way too long.

Unless all the wort has evaporated and your pot is scorched, you can keep on brewing! Just top off the wort with some extra water after you cool it down and carry on with fermentation. You might notice a more pronounced caramel flavor in your finished beer, as well as more bitter flavors and less hop flavor or aroma.

Brew Better Beer: A Companion to Beer School

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