HIGH KRAUSEN: Sarcastic Doorman

"High Krausen" is not, contrary to popular belief, the time when yeasts
hold tiny shoot-outs in your beer.  That actually occurs only during lagering.

Unsurprisingly, given that I massively over-pitched my yeast (that is to say, 100 billion yeast cells is a bit excessive for four liters of wort), fermentation is proceeding pretty rapidly and the beer is krausening like crazy.  The krausen is the foam which develops on top of the fermenting wort early in primary fermentation.  This is caused, I believe, by the CO2 produced by the yeast when it is metabolizing sugars pushing certain compounds out of the wort, and in some places (notably Germany), this foam is skimmed either to harvest yeast or simply to remove the compounds in it so that they are not reabsorbed into the beer; the foam can contain some of the harsher compounds found in hops, and removing it is supposed to yield beer with a smoother bitterness.  Modern "noble" hops, of course, contain far less of those compounds than would have been found at the time this tradition was started, and in some styles they are desirable anyway, so skimming the krausen is not often recommended for the homebrewer.

For some kind of perspective, I've got as much krausen on these four liters as I get on the average 23 liter batch, but it seems much denser.  I'll probably be moving this brew to the secondary almost as soon as the krausen falls, no later than Wednesday I think.