Efficiency & Diaceytl Rests
<editor's note> A Brewer's views on efficiency & diaceytl rests From a post to the HBD by George de piro </editor's note>
Date: Mon, 20 Jan 2003 22:39:53 -0500 From: George de Piro Subject: Lauter efficiency / diacetyl rests Hi all, Steve A. has pointed out that minimizing sparging most probably has a positive effect on beer flavor. There is another reason that brewers, particularly in Europe, like to not oversparge in the quest for efficiency: energy savings. One could attempt to eek out as much extract as possible from the malt by sparging, but one would then end up with an overly dilute wort that would require a lot of evaporation to reach the required gravity. Malt is cheaper than energy. The latest lauter tun designs strive to reach a low runoff gravity quickly, in other words, the rate of gravity drop in the runoff should be as high as possible so that dilute wort need not be collected. Modern breweries (esp. in Germany) like to keep evaporation down below 5%. Did I explain that well enough? - ---------- Somebody wrote in a few days ago asking about diacetyl rests. I haven't noticed a thorough explanation yet, so here goes: Diacetyl is formed when alpha acetolactate (AAL) is oxidized. AAL is made by yeast, and is not detectable by humans in the concentrations normally occurring in beer. The more AAL the yeast make, the more diacetyl potential the beer will have. Yeast can take up and metabolize diacetyl, thus reducing its concentration in beer below taste threshold, but they do not metabolize AAL. The idea of a diacetyl rest is to speed up the oxidation of AAL to diacetyl so that the yeast can metabolize it and the beer can get on with its life. Increasing the temperature of the beer will speed up these reactions. You do not necessarily have to perform a diacetyl rest for every lager, and you may sometimes need one for an ale. How can one tell if the rest is needed? Take two samples of the young beer into covered containers. 50 ml should be sufficient. Heat one sample to about 50C (140F or so; you need not be precise) for about 10 minutes (again, precision is not critical). Keep the other sample at cool room temperature. Cool the sample in an ice bath to be about the same temperature as the unheated sample. Smell both. Interpret results as follows: 1) If the unheated sample smells clean, but the heated sample smells buttery, there is an appreciable amount of AAL in the beer and the batch can benefit from a diacetyl rest. 2) If both samples smell clean, the AAL has already oxidized to diacetyl which was then removed by the yeast and no further action is needed on your part. Note that if this beer later develops buttery flavors, it likely has a bacterial infection (pediococcus). 3) If both samples smell of diacetyl, the beer is either badly infected or the yeast have not yet taken up the diacetyl that has formed. If it is not diminished after a few days at warm fermentation temperatures (i.e., diacetyl rest has no effect), then kraeusen with fresh, active yeast. If you do deem it necessary to give a cool fermenting beer a warm rest, do not worry about the temperature rising too quickly. Yeast do not really mind going from low to high temperatures (unless you cook them!). Yeast can be shocked into inactivity if they are chilled too quickly, though. Please note that removing the yeast from the beer, or otherwise hindering its activity, will leave nothing in the beer capable of reducing the diacetyl as it forms. Such a beer will become buttery over time. Have fun! George de Piro Head Brewer, C.H. Evans Brewing Company at the Albany Pump Station 19 Quackenbush Square Albany, NY, USA 12207 (518)447-9000 www.EvansAle.com Brewers of Kick-Ass Brown: Twice declared the Best American Brown Ale in the USA at the Great American Beer Festival (2000 & 2002)!
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