you have it in one.
it is the cells when they 'die' and the membranes fail they release nitrogen etc. into the brew.
for this to happen you need the beer to be left on the yeast for a long period of time at higher than fermenting temps. ie above 25 and alot of yeast left in the bottom.
most brewers will never even have this happen unless you get real lazy.
i guess the auto comes from this automatically happening if left for too long at these temps etc.
just to add the technical side.
courtesy of grumpys.
the association of brewers,dictionary of beer and brewing define autolysis as....
"the process of self-digestion of the body content of a cell by its own enzymes.the slow disintegration and breakdown of the membrane of yeast cells,in the fermenting medium,allows for the passage of nitrogen into the wort.
if too pronounced the autolysis process will give a yeasty flavour to the finished beer."
"Auto" comes from self, as in self digestion, releasing the cell contents into the brew. Although it is only likely to happen to an overpowering extent when you have high brew temps, lots of yeast, long contact time, it can also happen to a lesser extent without all those factors being present. I had a full on case in 1 brew, happened in the bottle not in the fermenter, when stored in a shed in Summer. But having now learnt exactly what it tastes like (people say vegemite, more dry bitter yeast flavour to me) I can sometimes taste a hint of it in other brews. I ended up throwing that brew out, but I should have kept a few for brew meetings as it really trains your palate to detect it.
I, just curious as to how strong the vegemite taste/smell is.
I havent had this happen yet but I've got 2 fermenters in the secondary going that I'll be bottling soon.
My house gets too hot in the summer. I've got wet towels around em but I'm not convinced it will be enough.
They are sitting at around 24 C.
Not looking forward to it but I really have minimal temp control.
In summer, drop the beer at day two, rack at day 5, get it in the bloody bottles ASAP--shd be very little yeast in the bottles
My Russian Imperial Stout that I entered into the Bathurst Beer Show had, according to the pro brewer there, a tiny touch of autolysis, faint enough it was a plus not a defect. That RIS had an OG of about 1100. . .
So I suggest, in summer, if you HAVE to brew, brew darker beers.
Johno, those wet towels don't do much unless you have a fan on them
"passage of nitrogen into the wort" - I assume this is the yeast's proteins and DNA (both of which contain N)... of the two I'd imagine the DNA would degrade very quickly, proteins though would probably hang about - it could be these causing the vegemitey flavour.