Lesson 7 - Beer Flavour and Stability SAQ
This lesson allows you to test yourself on the material covered in the lesson on Beer Flavour and Stability and determine the level to which you have met the learning outcomes.
Suggested Response - Q3
**Explain the contribution of hops to beer flavour. How can hops be used to enhance beer aroma?
Response:
Hops are unique ingredients in beer and provide the inherent characteristic bitterness and aroma. Over recent years, there has been an increase in demand for aromatic hoppy beers, driven by the US craft industry.
Bitterness in beer is derived primarily from the isomerised forms of the α-acids, the isohumulones. There are three isohumulones which exist in each of the cis and trans forms. These contribute to the different opinions on bitterness; the iso-cohumulone bitterness is said to contribute more of a harsh, unpleasant bitterness.
The brewer cannot change this through processing; it is a function of the hop variety they select for use. The variety of hop, its α-acid content, the quantity used in the brew, and the time of addition in the boil, will affect the beer bitterness – much of which can be lost during processing.
The hop acids are also important in creating off-flavours in beer. The lightstruck reaction between iso-α-acids and sulphur-containing thiol, mediated by sunlight and riboflavin, produces the potent and unpleasant skunky or lightstruck aroma.
The α-acids also contribute to stale or cheesy hop flavours, which are formed from the acyl side-chain oxidation that forms isovaleric and other acids.
Hop aroma is provided from the oil content of hops. There are hundreds of volatile aromatic compounds present in hops, and varietal differences are significant. Most hop oils are hydrocarbons such as myrcene, caryophyllene and humulene; however, it is the oxygenated forms of these that are particularly flavour active, such as linalool, limonene and geraniol. Even more so, are the sulphur-containing compounds which constitute < 1% of the oils and produce fruity aromas in beer.
Most of these aromatic oils are lost during boiling and brewers often employ techniques such as late hopping (at the end of the boil or whirlpool hopping to preserve the oils). Dry hopping is defined as adding hops in the fermentation or maturation processes. We know that yeast can play a role in the biotransformation of hop aroma compounds and for this reason some brewers add hops while yeast is still active.