way the beer is released from keg or can. Here
are some of the most interesting.
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); the water-avoiding ends project into the
gas while the water-loving ends stay in the
liquid, and thus reinforce the gas-liquid
interface. In beer, these molecules are mostly
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
noticeably more bitter than the liquid beneath.
Cool-fermented lagers generally give more
persistent foams than warm-fermented ales
because the latter contain more foam-
destabilizing higher alcohols from yeast