Lesson 6 - Process Aids and Additions

Bitterness is most commonly altered by using isomerised hop extract.

An iso-extract is a liquid solution that contains iso-α-acids (that contribute bitterness to the beer) at a certain concentration (usually around 30%) in the form of potassium salts. This post-fermentation bittering (PFB) allows for increased hop utilisation. This is because bittering potential is not lost with trub or yeast cells, or fobbing during fermentation – in fact, utilisation of over 90% is possible.

Brewers may vary their approach to post-fermentation bittering. Some will take at least 90% of their bitterness from the wort kettle, whereas some will take nearly all of their bitterness from post-fermentation. In some situations, it is preferable to add post-fermentation bitterness, for example if a brand is packaged into flint (clear) or green glass.

Beer has virtually no protection from light in these two types of glass. Light reacts with the kettle hop component isohumulones to create 3-methyl-2-butene-1-thiol (3MBT), causing an unpleasant ‘lightstruck’ flavour. This can also be described as ‘skunky’; it is highly undesirable in most beer brands. To avoid this, hops are not added to the kettle and instead, tetra iso-extract, hexa iso-extract and rho iso-α-acid hop products are used. These do not contain the vulnerable isohumulone component.

The types, use, and production of post-fermentation hop products are covered in detail in the Hops unit in the Diploma in Brewing 1 course.

These hop formats contribute three main benefits:

1. Provide a post-fermentation replacement for conventional bittering products in the brewhouse.

2. Light stability – provide protection against ‘light struck’ flavours.

3. In the case of tetra and hexa iso-extract, they greatly enhance beer foam and lacing in the glass.

Let us now summarise the overall benefits. The table below highlights some of the key attributes of using reduced hop extracts

Table: Comparison of benefits offered by reduced hop iso-extracts