Hops were originally added to beer as a preservative. Brewers quickly realised they also added a unique flavour to an otherwise sweet beverage. Ever since the 1516 German Beer Purity Law specifying that beer should contain only water, malt, hops and yeast, hops have been the prime flavour-enhancing ingredient. The alpha acid content determines the bitterness of hops. The amount of hops used and the length of time the malt and water mixture is boiled determine the amount of bitterness released into the beer. International Bitterness Unit (IBU) and Home Brew Unit (HBU) are two commonly used methods to calculate hop bitterness.
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Things you need
- Hop alpha acid rating (usually printed on package label)
- Utilisation chart (see Resources below)
Determine the weight, in ounces, of hops to be used.
Determine the alpha acid rating of the hops. This will be printed on the package label. Each variety of hops has its own alpha acid rating.
Determine the boiling time. Refer to the Resources link to get the utilisation factor from the boiling time.
Enter the following formula into your calculator to determine bitterness: IBU = (W * aa * U * 7489) / V Where "W" is the weight of the hops in ounces, "aa" is the alpha acid content of the hops, "U" is the utilisation factor (see the utilisation table on the Resources link), 7489 is a conversion factor for imperial units. "V" is the volume of water, in gallons, used in the boiling process.
Determine the alpha acid rating of the hops. Boiling time and volume are standardised for home brewing. Boiling time is one hour. The volume of the boil is five gallons. Both are standard for single-batch home brewing.
Multiply the alpha acid percentage by the weight in ounces of the hops used.
The answer provided by step 2 is the HBU rating.
Tips and warnings
- Since the alpha acid content of the hops decays over time and is affected by storage temperature and method, the HBU measurement is accurate enough for most home brewers and is much easier to calculate.
- In the formula for IBU, the " * " sign represents multiplication and the " / " sign represents division.
- When using metric measurements, grams and litres, omit the conversion factor of 7489 when calculating IBU.
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