Beer foam and head retention

Good foam creation, retention and glass lacing are the hallmarks of a well-made beer. Not only is foam visually appealing, it helps seal in and express aroma compounds. Gluten free brewers can occasionally struggle with getting good foam. Below are some positive and negative contributors to good foam quality.

Positive contributors to foam, foam retention and lacing

• Undermodified or raw (unmalted) grain high in proteins (e.g. quinoa, buckwheat, raw millet)
• For unmalted and less modified malted grains, a short protein rest at 55c/131f (<15min)
• For more modified malted grains, mash in at 63c-68c (145f-154f) to avoid further proteolysis (breakdown of proteins)
• Dark roasted grains
• some tannin extraction
• higher temp rest post saccharification at 73c/163f
• lots of low alpha acid hops during boil
• some dry hopping, esp noble hops
• shorter mash and boil times
• shorter protein chains are better dissolved and stay in solution longer?

Foam negative factors

• A dirty glass (including built up detergent residues, lipstick, and grease) can result in unappealing glasses with lots of nucleation sites -- small bubbles clinging to the sides of the glass -- and short lasting or non-existent foam. Proper cleaning of glassware can be the biggest improvement you can make. A simple solution for homebrewers is to clean beer glasses with an equipment / keg line cleaner such as PBW.
• Presence / extraction of lipids. Some grains, such as oats are naturally higher in lipids and on balance can have a foam-negative impact.
• Higher alcohol content
• Lower pH levels. For sour beer production, it can be helpful to pre-acidify the wort with lactic acid prior to adding lactic acid producing bacteria. This reduces the likelihood of unintentional infection and improves foam quality.
• Prolonged dry hopping (>2 days) and large dry hop amounts

Negative impacts of dry hopping

While hops and more specifically alpha acids and isomerized alpha acids can be foam positive, dry hopping can in fact have a negative impact on foam. Some solubilization of hop acids during dry hopping can be beneficial if contact time and concentration is limited. The negative impact culprit is likely fatty acids associated with hop oils which are made soluble by alcohol in the fermented beer. Different hop varieties will impact foam differently during dry hopping, though Cascade has been observed to be one of the worst for foam retention. Recommendations for altering dry hopping to promote foam include:

• limiting contact time to no more than 2 days
• limiting concentration of hop (i.e. use less volume)
• consider using hop extracts such as tetra-hydro, tetra-hexa, and iso which have been chemically altered to provide positive foam character with varying bittering impact

Further Reading

• The Secrets of Better Beer Foam (AHA, 2018)
• Discussion in Facebook group 'Saison, Bière de Garde, & Farmhouse Ale Appreciation Society', John Punt, December 14, 2019
• The Relative Significance of Physics and Chemistry for Beer Foam Excellence: Theory and Practice (Bamforth, 2004)
• Positive and negative impacts of specialty malts on beer foam: a comparison of various cereal products for their foaming properties (Combe et al, 2013)
• The Influence of Ethanol on the Foaming Properties of Beer Protein Fractions (Brierley et al, 1995)
• Getting Better Head Retention in Gluten Free Beers (Otherwise Brewing blog)
• Foam: Practical Guides for Beer Quality (Bamforth, 2012)
• A Review on the Source of Lipids and Their Interactions during Beer Fermentation that Affect Beer Quality (MDPI, Gordon et al, 2018)