On food and cooking the science and lore of the kitchen ( PDFDrive ) 1411

waythebeerisreleasedfromkegorcan.Here
aresomeofthemostinteresting.
Grain Proteins Stabilize the Head Foam
stability depends on the presence in the
bubble walls of emulsifier molecules with
water-loving and water-avoiding ends (p.
802);thewater-avoidingendsprojectintothe
gas while the water-loving ends stay in the
liquid, and thus reinforce the gas-liquid
interface.Inbeer,thesemoleculesaremostly
medium-sized proteins that come from the
malt or from cereal adjuncts, whose proteins
are more intact than malt’s and significantly
improve head stability. Hop acids also
contribute to foam stability, and become
concentrated enough in the foam to make it
noticeablymorebitterthantheliquidbeneath.
Cool-fermented lagers generally give more
persistent foams than warm-fermented ales
because the latter contain more foamdestabilizing higher alcohols from yeast


metabolism(p.762).
Nitrogen Makes Creamy Foams In the last
decade,manybeershavecometobeendowed
withanespeciallyfine,creamyheadthatused
to be largely limited to stouts. The creamy
headcomesfromanartificialdoseofnitrogen
gas that may be injected into beer at the
brewery, or in the bar or pub by the tap that
delivers beer from the keg, or by a small

deviceinsideanindividualbeercan.Nitrogen
islesssolubleinwaterthancarbondioxide,so
its bubbles are slower to lose gas to the
surroundingliquid,andslowertocoarsenand
deflate. Nitrogen bubbles remain small, and
persist. They also don’t carry the tart
pricklinessofcarbondioxide,whichbecomes
carbonicacidwhenitdissolvesinbeerandon
thesurfaceofourtongue.
Foam in the Glass An initially vigorous
pouringactiondevelopstheheadoffoamwith
asmall,easilycontrolledportionofthebeer.