Many compounds including iso-alpha-acids from hops and certain metal ions help stabilize these structures. However, fats and detergents tend to destabilize the bubbles and cause the foam to collapse. This is why adjuncts that are high in fat including oats and eclectic brewing spices with high oil contents such as coffee beans tend to decrease foam.

Also residual soap and detergents in carboys, kegs, and bottles will hurt beer foam. Settling out trub will decrease the amount of fatty acids in the beer. In contrast ingredients that are high in protein and glycoproteins will bolster beer froth. Some of the more common foam-positive ingredients include flaked wheat, flaked barley, wheat malt, and barley malt. Many brewers make a habit of adding a touch of wheat malt to every beer. At low levels the impact on flavor will be small while still imparting foam-positive characteristics.

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Beers also have different viscosities. Imagine beer foam as a matrix of bubbles in a liquid. The liquid drains down from the bubbles and back into the beer. Without any liquid surrounding them the bubbles pop and the foam collapses. In a beer with high viscosity, the liquid between the bubbles drains away slowly, so the head lasts longer.

Raw or flaked barley adjunct increases beer viscosity. Some homebrewers occasionally add a pound or two of flaked barley to pale ale type beers and Irish stouts. Beyond increasing head retention, the barley fills out the body of the beer.

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