Beer Foam | Part 1

The beer heads. This bulky and soft foam collar is part essential for drinking beer, and today will be the central topic of our article. Before reading, subscribe to this newsletter to receive good information about the brewing process!

Foam Goals

Intuitively, the drinkers know how important is the foam for the experience of drinking, either way, let’s mention it:

• Retain aroma. Aroma results from volatile compounds, and they tend to be eliminated in the first minutes after the pouring. The layer of foam helps keep it in the beer.
• Texture. The beer head provides texture and flavor for beer.
• Aesthetic. It demands no explanation, just look at the cover image!

Foam Formation.

There are two aspects to be analyzed, the head formation and the retention (stability of the foam). The foam is formed by the interaction of several proteins (protein Z, hordein species, and LPT1), isomerized alpha acids, metal ions, and carbon dioxide (or nitrogen gas).

Protein Z

Z is a high molecular weight albumin protein, often with a glycosylated (combined with a sugar molecule), and results from the Maillard reaction in the malting process. Protein Z acts as a structure for the foam. It comes from malt and is impacted by barley variety and malting parameters, but not for mashing steps. Malt with Kolbach Index (soluble-to-total protein ratio) higher than 40% tend to have high quantities of protein z.

Hordein Proteins

This protein family also comes from malts. It is insoluble until hydrolyzed in malting or mashing. The size ranges from 5.000 to 50.000. This protein can be broken in a proteolytic rest in mashing to improve the foam, but that will potentially increase the hazy active protein in the wort.

Hordein protein can replace the protein z in the structure functions, nonetheless, they are less stable, providing a worse retention of head.

LPT1

Lipid transfer protein 1, with the previous proteins, also comes from barley and wheat, formed in germination. In its natural form, it could act as hordein protein providing structure with low stability, however, after passing through long boiling (true for the brewing process) is denatured and could bind with protein z and hordeins, helping them to stabilize.

Iso-Alpha Acids and Metal Ions

They act as cross-links for proteins, improving the foam stability. The molecular structure of iso-alpha acid is important to define the stability, where isohumulone contributes better to head retention than isocohumolone. Pre-isomerized hop extract also has excellent impact stability, many breweries use tetra-iso hops as foam stabilizers (and for bitter, obviously).

Lipids

The lipids are naturally part of the wort coming from malts. Yeast can synthesize short fatty acids but with little impact in beer. It is expected that all lipids are removed in brewing process by spend grains and hot breaks. If present in beer, the lipids will break the bubble film, leading to foam collapse.

Gas

CO2 is essential to head formation. The bubbles are formed in the nucleation sites (impurities in the glass) then, while the bubble rises, the proteins are bonded around the bubble, forming foam. The size of the bubble, the solubility, and the active tension impact this complex equation. For example, beer carbonated with nitrogen tends to have more dense foam due to bigger bubbles, but also because nitrogen bubbles are slower, shocking less each other.

In the next article, we will understand the step-by-step foaming process.

Click Here to go to part 2.

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