of yeast growth occurs when the first yeast head arises from the fermenting wort, particularly in top fermenting beers.

“Cauliflower foam” is named after the appearance of the vegetable and is characterized by a thin, loose appearance. The foam rises high up out of the wort and is typically found after the first 12 hours of fermentation. At this point the yeast will be very active and producing large amounts of carbon dioxide. Large bubbles will be formed and as the surface layer of yeast will be relatively thin, these bubbles will be quite buoyant. Dark trub, made mostly of protein, will also be present in the early head and will provide further stability to the bubbles that rise up into the fermenter headspace, producing a craggy foam.

Cauliflower heads are an important indicator that a fermentation is well under way and should be present within 24 hours of the onset of fermentation. In many breweries the cauliflower head is removed because it is likely to contain dead yeast cells carried over from the previous brew. It is undesirable for these cells to return to the wort where they can release unwanted flavors. An early skimming of these yeasts and of the residual trub is advised in order to obtain a cleaner-tasting beer.