Hops are natural produce whose bitterness can vary slightly from season to season. It is possible to tell how bitter hops are by observing the alpha acid % on the packet. The higher the percentage the more bitter, and so sometimes less or more is needed to achieve the same bitterness.
In order to achieve consistent results use the FORMULA below to determine how much hops to use, either of varying years of the same hop variety or different substitute varieties.
NEW WEIGHT OF HOPS BECOMES:
QUANTITIY OF SPECIFIED HOPS X ALPHA OF SPECIFIED HOPS
DIVIDED BY ALPHA ACID OF SUBSTITUTE HOPS
Assuming that the recipe calls for 40 grams of Challenger which has an Alpha Acid content of 7.6 percent and you want to use Golding that has an apha acid content of 5.7 percent
NEW WEIGHT OF HOPS BECOMES:
EXAMPLE: 40g X 7.6%AA
------------------------- = 53 GRAMS
If you know your boiling losses and the pre-boil specific gravity, you can estimate the post-boil original specific gravity (OG) of your beer with reasonable accuracy. The formula for calculating the approximate post-boil OG is:
Post-boil gravity points = (Pre-boil volume * pre-boil gravity points) / Post-boil volume
Specific gravity “points” (or GP) are the portion of the specific gravity reading to the right of the decimal point multiplied by 1000. For example, a specific gravity of 1.050 is 50 points.
Using the pre-boil and post-boil volumes from the example above, with a pre-boil specific gravity of 1.036, the projected post-boil OG would be 1.049.
(7.5 gallons * 36 GP) / 5.5 gallons = 49 GP (equivalent to SG 1.049)
Calculating the post-boil OG at the beginning of the boil is valuable because this is the easiest point to make adjustments. If the calculated OG differs appreciably from the target for the recipe, additional extract or water can be added.
To increase the gravity of a 5-gallon (19 L) batch by approximately 1 GP at the end of the boil, add 2.5 oz. (72 g) — roughly one-half cup/118 mL — light dried malt extract, or approximately three-quarters cup (177 mL) liquid extract.
To decrease the gravity of the same batch by approximately 1 GP, add 24 fl. oz. (710 mL) water prior to boiling.
You can also manipulate the OG by changing the boiling time. In the above examples, a 9-minute increase in the boiling time will raise the OG by approximately 1 gravity point, while decreasing it by 9 minutes will lower it by approximately 1 point. The approximate change in the post-boil volume per 9 minutes will be 22 fl. oz. (640 mL).
This information on yeast strain sources and comparisons between White Labs and Wyeast was put together by Kristen England. He says, "I tried to get the exact source of each breweries yeast and if I was confident I was correct I put the original brewery. If I have evidence of a yeast strain but NOT 100% confident I put my idea and a '?'."
So how do I choose the right hops for my beer? With such a wide range of flavor and aroma characteristics, this chart can serve as a helpful guide to more than one hundred varieties. Whether you are trying to duplicate a style or are looking to experiment, the following list can help to get you started. Just select a beer style and a chart will pull up with appropriate hops to consider for your recipe.