The source of braunhefe and whether or not to remove it has been a matter of conjecture and discussion among homebrewers over the years on HBD and when we get together at meetings or NHC.
Based on the observation that I get more with a heavily hopped beer, and that the currently fermenting SS Minnow Mild (16.5 IBU) had nearly none, it seems pretty clear that it's at least partly from hops, maybe with some break material in it as well. It has an almost waxy feel (presumably from hop resins) and is unpleasantly, and intensely bitter.
Over the years on HBD, some argued that if left in, it would impart an unpleasant, harsh bitterness to the finished beer, and other argued that if you removed it, you were removing some of the hops bitterness that you paid good money to get into the beer.
When the attendees of MCAB II visited the A/B pilot brewery in St. Louis ten years ago, the head brewer for that unit (whose name escapes me now) gave us a complete, behind the scenes tour. This is a 15 barrel exact miniature of their regular breweries. One things he pointed out was that the fermenter was designed so that the kraeusen rose exactly to the underside of the top, where the braunhefe stuck. When the kraeusen fell, it left the braunhefe behind. Of course, A/B has exact repeatability, so this works for them.
I do all of my ale fermentations in a cut-off Hoff Stevens 1/2 bbl keg, and when the very thin layer of braunhefe rises to the surface on the first or second day, I skim it off. This is before the yeast rises (I almost always use a top fermenting yeast, most often WLP Essex). This is mostly a habit based on these old discussions, though I'm not certain it's necessary, but see de Klerk below.
I ferment lagers in oversized carboys, so I can't remove it, but since I rack the beer into kegs when fermentation is still active but slowing, I can leave it behind as it floats on the surface of the little bit of foam that remains at this stage.
Here is what the only professional text (the 1957 standard reference "A Textbook of brewing" by Jean de Klerk) I have says:
On managing top fermentations (pp. 409-410), "This brings us to the third stage of fermentation. The head gradually falls in and finally forms a brown, bitter-tasting cover. The brown colour of the cover is due to the oxidation of resins and tannins." He then writes that you must rack to the conditioning tank when there is 0.8 - 1.0% fermentable matter left, and then "the cover of scum that forms at the surface is carefully skimmed off and discarded."
On managing top fermentations, he writes (p. 411), "Since the cover of dirty material on the surface cannot be skimmed off at the end of fermentation because it is mixed with the yeast, it is removed before the yeast starts to purge from the wort."
All that said, I don't think that all professional brewers do skim.
Topic: Kraeusen removal, what difference does it make (Read 13295 times)
