The BrewMeister - What About Alpha Acids

What are Alpha Acids?

Alpha Acids are the oils in hops that make your beer bitter.
Alpha acids are bittering compounds found in hops that are extracted
when hops are boiled with wort. The alpha acid "rating" on hops
describes how much of the weight of the hop is made up of alpha acids.
Hops with a higher alpha acid content will contribute more bitterness
than a low alpha hop when using the same amount of hop.

They can also be referred to as AAU's or Alpha Acid Units.
They are also referred to as HBU's or Homebrew Bittering Units.
Note that volume is ignored in the HBU, therefore it
is important to include the volume of the recipe, or express the
hop additions in HBU per gallon (or HBU per 5 gallons) rather than
just strictly HBU.

Compounds derived from hops determine the bitter taste of beer. Hops and hop extracts used in the wort boiling process contain three main alpha-acids (humulone, cohumulone, adhumulone) and three beta-acids (lupulone, colupulone, adlupulone). During wort boil, six iso-alpha-acids are formed from the three hop alpha-acids. Control of the contents and ratio of alpha- and beta-acids in hops and the concentration of iso-alpha-acids in wort and beer is very important for the brewery, because bitterness is one of the main flavor and taste characteristics of beer.

A number of analytical techniques have been developed for determining concentrations of alpha-acids in hops and iso-alpha-acids in worts and beers. The methods employed by the hop and brewing industries for alpha-acid and iso-alpha-acid quantification are based on lead conductance, ultraviolet spectrophotometry, and high-performance liquid chromatography (HPLC).

Recent papers presented by Belgian and German chemists have demonstrated a new sample preparation technique named stir bar sorptive extraction (SBSE) followed by HPLC. We have connected a sample preparation technique SBSE with micellar electrokinetic chromatography.

For determination of both acid types (hop alpha-and beta-acids and beer iso-alpha-acids), the same buffer and electrophoretic conditions are proposed.

For analysis of iso-alpha-acids, the sample preparation by SBSE is used. Application of this method allows control of hop and hop-product quality, the transformation of these compounds during technological processes, beer bitterness, and degree of oxidative deterioration of beer.

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