In this installment of our Exchange Rates series, we take a look at how hops amounts may or may not need to be changed when converting a recipe from an all-grain formulation to one built around extract. Hops quantities may require adjustment to
- Account for different boil volumes
- Account for different alpha acid percentages
These often-overlooked adjustments can mean the difference between a super hops bomb and a lackluster shell of an IPA.
Boil Volume Adjustment
Hops utilization refers to how much of a hops’ available alpha acid content is converted into bitter iso-alpha-acid during the boil. Generally speaking, denser wort yields less utilization, so if you boil a concentrated wort instead of a full-batch volume, you might need to use a larger bittering hops charge to get the same effect. But calculating how much more you need is a bit tricky without brewing software.
An easier way to account for a smaller boil volume of concentrated wort is to use a technique called Late Extract Addition. With a late extract addition, you only add enough extract initially to bring your partial boil to about the same gravity as you would have in an equivalent full boil. You conduct the boil using the same hops as you would for a full volume, and then you add the remainder of the extract about ten minutes before the end of the boil to sanitize.
For example, let’s say you can only boil 2.5 gallons (9.5 liters), but your recipe calls for a full 5-gallon (19 liters) boil. To perform a late extract addition, simply add half of the extract up front and dose with hops as indicated in the recipe. Then about ten minutes before the boil is complete, add the rest of the extract. This way, your boiled wort density is roughly the same as it would be had you boiled the whole thing.
Alpha Acid Adjustment
Alpha acids (AA) are the chemicals in hops that contribute bitterness to beer. When alpha acids are boiled, they are isomerized, which is to say their chemical structure changes. The resulting so-called iso-alpha-acids make beer bitter, but they don’t contribute much in the way of flavor or aroma.
Different hops varieties have different alpha acid percentages, and even the same variety will vary from one year to the next. So, when converting a recipe, it may be necessary to adjust hops amounts—especially for hops boiled for more than half an hour—to account for differences in alpha acid percentage.
Let’s say you’re converting a recipe that adds 1 ounce (28 grams) of Magnum hops 60 minutes before the end of the boil and that the recipe specifies Magnum as having 12 percent alpha acids. But the Magnum hops in your freezer are only 10 percent alpha acids.
To account for the lower alpha acids in your hops, you’d simply increase the amount proportionally by weight. Since the original recipe’s Magnum hops are 20 percent higher in alpha acids than yours, you can use 20 percent more by weight, so 1.2 ounces (34 grams) at the 60-minute mark.
This also works if you are using an entirely different hops for bittering, which is common since the specific bittering hops variety won’t affect the final beer much, if at all. So if you don’t have Magnum in your freezer, but you do have some 14 percent Columbus, then you might choose to replace the Magnum in the recipe with Columbus, but use 0.86 ounces [(12% ÷ 14%) × 1 ounce] or 24 grams.
Unless your recipe features very large amounts of late kettle hops with high alpha acids, you can usually ignore differences in alpha acid for hops added more than half an hour into the boil. But with so many of today’s popular recipes using hop bursting techniques, it may pay to perform the conversion for all but the dry hops.
Hops adjustments are the final piece of the puzzle in converting all-grain recipes to extract versions. In the next and final installment of the Exchange Rates series, we provide a complete example and work through the math to bring it all together.