Lesson 2 - Beer Foam

While foam is not necessarily the primary reason for raw material selection and beer processing activities, there are certainly some considerations that can be used to improve beer foam. Let us take a closer look.

Malt

Higher protein malt will, in general, have higher levels of foam stabilising protein. This needs to be considered, along with lower extract and higher haze potential (foam potential would not outweigh these considerations).

We may believe that varieties with higher Z4 or LTP1 protein could be used to enhance foam, however, in practice, this is difficult to do as the specific protein content changes yearly depending on the growing conditions. The decision becomes more difficult because processing conditions affect how much protein survives in the finished beer.

If we consider the malting process, undermodified malt (with high β-glucans and low (FAN) Free Amino Nitrogen), will result in the finished product having poor characteristics such as incomplete attenuation and hazy beer. These attributes would outweigh any potential foam benefit from increased protein content. Also, undermodified malt is difficult to process through the brewhouse and filtration areas.

Speciality malts are generally considered to be foam-positive. These include wheat malt, caramel or crystal malts and dark malts. It has been shown that the proteins from wheat have better foam stabilising properties than the ones from barley. Wheat also contains lipid-binding proteins that can remove foam-negative lipids.

Overall, wheat malt is known to assist foam.

Caramel malts, particularly lighter products are often marketed as foam-positive. However, recent findings have shown that some of these products are in fact, foam-negative. This is due to lipids and oxidised lipids that destabilise foam bubbles, causing coalescence. Darker coloured malts contain melanoidins formed from protein amino acid and carbohydrate sugar reactions. Glycosylated proteins are more flexible, which enhance their foam promoting properties.

Black malt, together with roast barley, are very foam-positive overall. Their foam-positive complexes form during roasting, giving a net foam-positive effect. These malts are used successfully to assist foam stability in porters and stouts, but their use is limited to very dark beers (to make an impact).

This research, published in 2014, is presented here:

Adjuncts

The grits and starch of starchy cereals are foam-negative when used as an adjunct as no nitrogenous material is introduced, so the net protein level in the grist will be diluted. As mentioned, wheat flakes, however, are an excellent foam improver for brewers.

It is important for the brewer to adjust malt FAN levels upwards when increasing adjunct content. Low FAN levels can cause yeast stress and secretion of proteinase A which will negatively affect foam formation.

Hops

The principle foam stabilising interaction in beer foam is achieved through the interaction of hydrophobic protein and iso-α-acids. Hop products with higher isohumulone ratios are more foam stabilising than those with higher iso-cohumulone levels. Hydrogenated (or reduced hop products) are more foam positive than the iso-α-acids.

Even a small addition of 3 mg/L of tetra iso-α-acid (Tetra/Tetrahop) can give a 20% improvement in foam and a 40% improvement in lacing.