Lesson 3 - Beer Foam SAQ

** You have been asked to develop a new beer that has a high foam stability. How would you choose your ingredients and optimise the brewing process to improve the foam stability?

Response:

This question is primarily focused around foam stability without specifying the style, so in the answer, we can consider the components in beer that either promote or destroy foam and how we use these to create a foam stable beer.

• Extract bearing materials

Here we would choose 100% malt to maximise foam protein. Starch-based adjuncts such as maize do not contribute foam-positive polypeptides and can be high in lipids, which causes bubble coalescence and collapses foam.

If the malt is dark and high in nitrogen (protein) it will help foam. Darker malts contain melanoidins which are formed from protein amino acid and carbohydrate reactions.

It would be a good idea to include some wheat malt in the recipe because it is especially stabilising for foam.

Undermodified malt may seem a good option. It contains higher β-glucans which increase viscosity, retarding drainage, therefore maintaining a higher level of proteins at the bubble interface. Using undermodified malt, however, is a case of the ‘tail wagging the dog’ in that other problems arise, such as poor filterability, lower extract recovery and colloidal (haze) problems.

• Hop acids

The hop acids, and specifically the hydrophobic isohumulones, stabilise beer foams by binding and cross-linking to foam proteins in the bubble layer. We would thus want to create a bitter beer with higher levels of hop acids.

• Yeast performance

Yeast management should be a focus area, with processes to:

• • Avoid old yeast re-use

  • Removal of yeast on time

  • Optimal storage and turnaround time

Under stressed conditions, brewing yeast releases proteinases, particularly proteinase A. This gradually digests the foam stabilising proteins, resulting in poor foam stability on pouring. In order to avoid yeast stress, our beer should be brewed at standard gravity.

This will result in a lower ethanol concentration. Ethanol is foam-negative acting in a way analogous to lipids, disrupting protein and iso-α-acid complexes in the bubble boundary layer.

Healthy yeast also removes foam destroying lipids.

• Cations

Cations, particularly zinc, are positive to foam stability when added post-fermentation. They bind to and link the hop acids and foam stabilising proteins, linking them together to form a stable complex.

If zinc is deficient at the start of fermentation it will affect yeast health, and for this reason, zinc in the form of zinc sulphate is added during wort cooling.

• CO₂ and N₂

The CO₂ content of beer is the basis for beer foam. Our beer would have sufficient CO₂ content to support foam stability through constant replenishment of collapsed foam bubbles with new ones, known as beading.

The addition of a small quantity of N₂ gas at packaging (~30-40 mg/L) will produce a stable foam.