What's the Difference Between Alpha and Beta Acids in Beer?
Posted by Matteo Lahm on 6th Dec 2024
Alpha and beta acids are the two main types of hop acids that contribute to the flavor and aroma of beer. Alpha acids are responsible for the bitterness, while beta acids provide the floral and fruity aromas. The ratio of alpha to beta acids in beer can vary greatly, and understanding the differences between these two types of acids can help you create your perfect beer.
Alpha acids are the most common type of hop acid found in beer and are typically present in concentrations of 3-10%. Alpha acids are derived from the lupulin glands of the hop plant, and are composed of humulone, cohumulone, and adhumulone. When boiled, alpha acids are converted into iso-alpha acids, which are more soluble in water and are responsible for the bitterness.
Beta acids are responsible for the floral and fruity aromas and are typically present in lower concentrations of 0.5-3%. Beta acids are also derived from the lupulin glands of the hop plant, and are composed of lupulone, colupulone, and adlupulone. Unlike alpha acids, beta acids are not converted into iso-beta acids when boiled.
Why the difference? Beta acids are not thermally stable. They are sensitive to heat and will break down into other compounds when exposed to high temperatures. This breakdown is known as thermal degradation and results in the formation of iso-beta acids, which are different from the original beta acids. Alpha acids, on the other hand, are thermally stable and can withstand higher temperatures. The heat causes the alpha acids to undergo a chemical reaction known as isomerization, which rearranges the atoms in the molecule to form a new compound which has a different chemical structure.
The ratio of alpha to beta acids in beer can vary greatly and can have a significant impact on the flavor and aroma of the beer. A beer with a higher ratio of alpha to beta acids will be more bitter, while a beer with a lower ratio of alpha to beta acids will be more aromatic.
Examples of different proportions of alpha and beta acids in different kinds of beer include:
- India Pale Ale (IPA): Alpha acids: 8-14%, Beta acids: 2-4%
- Pale Ale: Alpha acids: 4-7%, Beta acids: 1-2%
- Pilsner: Alpha acids: 3-5%, Beta acids: 0.5-1%
- Stout: Alpha acids: 5-7%, Beta acids: 0.5-1%
You can control the ratio of alpha and beta acids in your beer. By adjusting the amount of hops used in the brewing process and/or by adding more or less hops, you will influence the ratio of the two acids. This can also be done by using different varieties of hops. Various hops contain different levels of alpha and beta acids and the ratio of these acids differ from variety to variety.
Examples of hops higher in alpha acids include:
Examples of hops higher in beta acids include:
Manipulating the amount of alpha and beta acids in beer making is a delicate art that requires precision and understanding of the brewing process. Alpha acids are extracted from hops during the boiling process. The longer the hops are boiled, the more alpha acids are extracted. Therefore, if you want to increase the bitterness of your beer, you should add the hops earlier in the boil. Conversely, if you want to decrease it, you should add the hops later in the boil or even after the boil has finished.
Beta acids, on the other hand are extracted at lower temperatures and evaporate quickly when boiled. Therefore, if you want to enhance their aromas, you should add the hops at the end of the boil or during the fermentation process, also known as dry hopping. However, if you want to reduce the aroma, you should add them sooner. The timing and temperature of adding hops, therefore, play a crucial role in determining the ratio of the two acids, and subsequently, the taste and aroma of the beer. If you are using one type of hops and want a good extraction of both acid types, break up the dosage and add one earlier in the boil and the other later. You can choose your ratio depending on your preferred taste.
Understanding the chemistry of alpha and beta acids and how they are produced is essential. Learning which hops to use and how to control the alpha/beta ratio is one of the main aspects of crafting your desired flavor profile. Good luck!