Lesson 10 - Hops Final SAQ

**“The IBU value of beer can mislead the consumer as what to expect with regards to bitterness”. Do you agree or disagree? Support your answer with relevant facts.

Response:

In order to argue this statement, you need to first define what an IBU is. An IBU is the abbreviation for the international bitterness init. It is measured using spectrophotometry and considered as being equivalent to 1 mg of iso-α-acid in 1 L of wort or beer.

Based on this, it is clear that the IBU could be misleading, as there are other components in hops that provide bitterness – especially if the beer is dry hopped.

Bitterness can be provided by α-acid, oxidised α-acid (humulinones), β-acids and polyphenols.

The unconverted α-acids provide bitterness, although they are not very soluble in beer; their overall bitterness is only about 10% of the iso-α-acids. Any α-acid that survives unchanged in the final beer has likely come from dry hopping. The majority are converted to iso-α-acid during wort boiling or are present in their oxidised form.

The oxidised α-acids, known as humulinones, are extremely soluble in beer and impart a bitterness that is roughly 66% as bitter as the iso-α-acids.

β-Acids are not isomerised during wort boiling, but those that survive into the beer can be converted into oxidative transformation products, known as hulupones. These provide a pronounced bitterness to beer. There are not many β-acids in beer, as the initial quantity is about a quarter of the amount of α-acids, and only about 20% of these β-acids survive into the beer.

Hard resins, although not necessarily bitter on their own, have been shown to have an additive effect on the bitterness of the iso-α-acids, thus contributing to the overall sensorial bitterness of the beer.

Polyphenols can provide astringency (astringency differs from bitterness by having a mouth puckering quality, like sucking on a teabag) and bitterness to the beer. Aroma hops, which are the most likely to be used in dry hopping, tend to have a higher amount of polyphenol than bittering varieties. It is thus likely that the polyphenol content in these beers will affect the overall bitterness.

Dry hopping tends to increase the pH of the beer; this increased pH can increase the perceived bitterness of beer.

It has been suggested that a better estimation of the bitterness is not just the iso-α-acid content, but rather this equation:

Sensory Bitterness = iso-α-acid + (0.66 x humulinone) + (0.10 x α-acid)

Although this does not consider the polyphenol contribution or the effect of residual sugar and alcohol, it is more accurate than just the iso-α-acid value alone.