People like session beers, but people love big beers. They can be tough to brew, so what follows is an outline of issues and tips for successful high gravity brewing. Appropriately, this post is a big’un.
BJCP substyles in the 7%-and-up range include:
Doppelbock/Eisbock Baltic Porter Foreign Extra Stout
Russian Imperial Stout Imperial IPA Weizenbock
Dubbel Tripel Golden Strong Ale
Dark Strong Ale Old Ale Barleywine
And of course there’s the Specialty category, which can include any other high gravity or “imperial” beer you might conjure up. Those are always fun.
2. Recipe Design
First things first: Ensure your recipe contains enough fermentables that yeast can convert to alcohol. This will mean using several more pounds of malt (or an extra can or two of malt extract) than you use in a typical average-strength beer recipe.
The bulk of that malt should be composed of base malt(s), like Pale or Pilsner malt. Base malts contribute the greatest amount of enzymatic activity to convert starches into fermentable sugars during the mash. In contrast, specialty malts and adjuncts, like Brown malt or rice, contribute far less—or no—enzymatic activity, and require the enzymes from base malts to convert their starches.
Another method of increasing fermentables and gravity involves adding adjunct sugars during the boil. Common adjunct sugars include honey, maple syrup, molasses, and candi sugar. If overdone, they can impair fermentation and leave behind a phenolic character, so always use in moderation.
Once your recipe is optimized for higher gravity, you’ll need to use enough yeast to actually convert those fermentables into alcohol. A good rule of thumb for high gravity brewing is to use 2 vials or packs of yeast for a 5gal batch. A better rule of thumb is to prepare a few days ahead of time and make a large yeast starter, roughly 3 or 4 liters. An inadequate quantity of yeast will result in those cells being overworked and stressed, which in turn will result in flaws in your beer. Not to mention, you risk not achieving your desired final gravity.
Before pitching yeast, but after chilling, aerate the wort extra thoroughly. High gravity wort, by definition, is dense and yeast will require sufficient oxygen to reproduce and grow without being overwhelmed. There are a few different ways to aerate wort, including vigorous stirring or submerging an oxygen stone.
When choosing a yeast strain, ensure the strain has adequate attenuation and alcohol tolerance. Attenuation refers to the relative amount of fermentables the yeast will consume and its ability to reduce the gravity of the beer. Alcohol tolerance refers to the strain’s ability to continue fermenting in the presence of increasing levels of alcohol. A strain, even if highly attenuative, could begin to die off if it cannot tolerate abv levels above, say, 7 or 8%.
Finally, although hops won’t affect gravity or alcohol content, consider using more hops than your typical average-strength recipe—ales especially. Depending on style and desired characteristics, the added bitterness and hop flavor will help to balance the potential sweetness and intense malt flavors of a high gravity brew.
3. Brewing Process
To create wort that is more highly fermentable, mash between 140 and 149 F. This is the ideal temperature range for beta amylase, which is the enzyme responsible for breaking down starch chains into their most fermentable form. On the other hand, to create wort with higher levels of dextrins, mash in the 150-158 F range. Many brewers mash at 150-152F for a more even balance of dextrins and fermentable sugars, and are still able to achieve a high abv.
Boil volume is one factor many homebrewers overlook when brewing high gravity beers. Many simply calculate water volumes for the mash and sparge like any other recipe, resulting in a boil volume of approximately 6.5gal for a 5gal batch. Nothing wrong with that, but . . .
. . . If you’ve got the equipment, consider boiling 7 or 7.5gal instead, and for as long as it takes to boil down to about 5.5gal. This method lets you collect more fermentables and dextrins from the sparge. By boiling longer and condensing the wort, you’ll develop more complex aromas and flavors.
Similar to mashing, you can control temperature during fermentation to create the best conditions for yeast in a high gravity beer. Ferment in the temperature range specified for the yeast strain being used. For ales, this will be around 62-74 F. Lagers will be in the 48-55 F range.
If the temperature is too cold during primary fermentation, yeast will become sluggish or, worse, dormant. In other words, fermentation may slow down or stop altogether.
If the temperature is too hot, yeast may create excessive esters and higher alcohols, resulting in a solvent-like aroma and flavor. Or, yeast may begin to die off, which can result in an incomplete fermentation and off-flavors and -aromas.
This final factor could either be the easiest or the hardest thing for a brewer to accomplish: Do nothing. Seriously, leave the beer alone once it has been transferred to the secondary fermenter. High gravity beers take longer to ferment completely, and age can do wonders to the flavor and aroma profiles of a high gravity beer.