Foam Development & Retention

                                                                                                          by Mike Retzlaff

Beer, soft drinks, and sparkling water have some things in common.  All have some fizz and can slake your thirst, but some won’t raise a lasting head of foam. 

Foam is obviously due to the creation and release of bubbles. Gas bubbles in soft drinks and seltzer are rather large and generally don’t form a head.  When beer is dispensed, from tap, bottle, or can, the gas comes out of solution and rises as bubbles in the column of beer.  If the bubble walls are strong enough to maintain integrity in their shape when they get to the top, they’ll collect as foam and can sustain themselves for quite some time.  There is something in beer which gets into the bubble walls to increase surface tension which keeps the bubbles from bursting.  It’s simply a matter of physics.

The old commercial standard was a minimum of 50% foam retention over one minute.  Many well made beers exceed that standard while others, sadly, don’t come close.  Keep in mind that beer foam is about 25% beer.  As beer conditions, CO2 is converted to carbonic acid gas – H2CO3.  While all beer styles differ in their color, flavor, aroma, and bitterness, some well made beers can have a rocky head, some have a creamy layer of foam, and others maintain a minimal but persistent collar. Much of this depends on the volume of gas dissolved in the beer.

It is therefore a matter of the viscosity of the bubble walls which determines foam development and head retention.  One wort constituent that possesses this power more than all others is albumose.  Although it does strengthen bubble walls, its existence in excess causes a problem with the brilliancy and stability of the beer.  This is one of the problems with the current fad of “Juicy IPAs” and “NEIPAs.”  The chemistry works against a brilliant beer and “hazy” is marketed as desirable.  The majority of the hopping is made after the boil, either as a steep in the kettle, in the whirlpool, or in the hop-back, and doesn’t contribute much in the way of IBUs.  The foam supporting components supplied by hops, simply aren’t in the beer.  Many of these beers do indeed raise a nice head of foam but retention isn’t what it could be.

In practice, probably the best method of steering away from bad head retention and foam instability, is mashing fairly stiffly and at a comparatively low initial heat.  An example might be a mash rest of 145° F (63o C), then after twenty minutes, quickly raising the temperature of the mash by means of a hot underlet or a step infusion of brewing liquor of about 200° F (93o), to achieve 158o to 160° F (70o to 71o C).  This will encourage proteolytic action and the high heat will help fix the dextrins.  The dextrins are of great importance in head retention. 

Polysaccharides and melanoidins also promote foam stability.  On the other hand, over-modified malts, owing to the degradation of the protein during the malting process, may also be responsible for poor head retention. 

When mashing at normal saccharification temps, 150o to 155o F (65o to 68o C), the late George Fix was a proponent of an additional rest at 160o for 10 minutes.  This helps develop glyco-proteins which are polymers of dextrins and middle to high molecular weight proteins which also promote foam stability. 

There are a large group of proteins and polypeptides which can act as a group and individually as foam producing agents.  LTP1 (lipid transfer protein 1) occurs naturally in barley.  It has a major role in a beer’s foam stability.  LTP1 has a high rate of “hydrophobicity” (it repels water), so in order to help alleviate its predicament, it grabs hold of a gas bubble as it rises to the surface.  Yeast, in poor health (under pitched, under oxygenated, or insufficient nutrients), can break down LPT1 and help destroy foam potential by enzymatic actions.

Once at the surface, the LTP1 protein forms a coating on the bubbles which helps maintain the foam.  Hops also come into play as the hydrophobic polypeptides derived from grain cross link with bitter iso-alpha acids from hops to render foam more rigid, stable and clingy.

There are dozens of variables that impact the differences in head-foam quality, texture and retention, but quantities of LTP1 in a specific batch of beer can be traced back to factors like how wet or warm the climate was that produced the barley (terroir).

Foam’s Effect on Flavor

A beer often tastes different when capped with a nice head of foam, and this is due to surface active compounds that move into the bubble walls as they percolate to the top of your glass. Foam also carries “taste” effects which are actually perceived physically.  The “hot” effects of chili peppers and the “cool” effects of mint don’t deliver an actual change of temperature but they do induce a physical sensation and perception.  The creamy, fluffy feel of foam can truly alter the perception of a beer by “softening” the overall mouthfeel.

It’s important to remember that our senses of taste and smell are intrinsically tied.  The majority of what we call “taste” is actually smell.  The various aroma compounds released by the foam are, in large part, what can make a beer so enjoyable and memorable.  The foam opens up the full range of flavors and presents them to your senses.

The Esthetics of Lacing

Whether a beer has a giant rocky head as in a German Weissbier or the small collar of a fine English Pale ale, lacing is another indicator of a properly brewed and conditioned beer.  The LTP1 proteins mentioned earlier, which form a coating around every gas bubble, interact with other compounds that cause them, in turn, to rise to the top of your glass.

These proteins and compounds begin to interact with one another and become denser.  They undergo a transition of texture and, when having a sustained contact with the sides of the glass, begin to stick. This is why a beer sipped slowly will accumulate much more lacing than one that is guzzled.

Causes of Poor Foam Retention

  1. Excessive protein rest
  2. Over-modified malt
  3. Too high an adjunct ratio
  4. Lipids in ferment (excessive sparging, autolyzed yeast, insufficient hot & cold break)
  5. Over foaming in fermenter (usually due to excessive fermentation temperature)
  6. Insufficient or deteriorated hops
  7. Contact with oils or grease (at any time including the point of pouring in a glass)

Soap, grease, lipstick, etc. are the enemies of beer foam.  It is important to keep your glassware “beer clean.”  An excellent article on the subject can be found in this link:  

https://content.kegworks.com/blog/beer-clean-glass

Conclusion

The brewing of a proper beer begins with the selection of the right ingredients.  It continues with procedures including sanitation, mash regimen, boiling, hop selection and utilization, fermentation, packaging, and dispensing.  It seems like a lot but so did the first several beers any of us brewed.  It is important to keep learning and to incorporate what we’ve learned into practice.

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