HOMEBREW Digest #5606 Fri 11 September 2009

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  Attenuation ("A. J. deLange")
  Re: Attenuation (Kai Troester)
  RE: Attenuation ("RJ")

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---------------------------------------------------------------------- Date: Fri, 11 Sep 2009 08:26:46 -0400 From: "A. J. deLange" <ajdel at cox.net> Subject: Attenuation Attenuation is intended to be a rough indicator of the amount of specific gravity decrease over the course of a nominal fermentation with the yeast strain in question. Formally it is ADF = 100 X (OE - AE)/OE where ADF = "apparent degree of fermentation" (attenuation) in percent, OE = "original extract" and AE = "apparent extract". OE and AE are in grams of extract per 100 grams of beer i.e. extract concentration w/w i.e. degrees Plato but in common usage, especially by homebrewers, they are in specific gravity "points" (e.g. a wort with SG 1.040 has 40 points of OE). More meaningfull is the "real degree of fermentation" RDF = 100*(OE - TE)/OE where TE is the "true extract" of the beer i.e. the actual number of grams of extract in 100 grams of beer but measuring that is appreciably more troublesome that just taking a hydrometer reading on the fermented beer so few do it but you can estimate it from RDF = 3.271 + 0.766*ADF. I expect the answer to the question as to where the numbers on the yeast specs come from is that the manufacturer does test fermentations with nominal worts under nominal conditions for the particular strain (ale yeasts would be operated at higher temperatures than lager yeasts) and records the range of ADF's found. The ADF is going to depend on several factors such as the composition of the wort (dextrinous worts will not ferment to the same extent as highly fermentable ones i.e. ones mashed to produce lots of fermentable sugars as opposed to the larger, non fermentable ones), its OE, the presence of sufficient yeast nutrients and enzyme co factors, the temperature at which the fermentation is conducted, the pitching rate, the amount of oxygen supplied and when it is supplied and the, ability of the yeast to transport and lyse the various sugars available in a wort, the relative amounts of those sugars, how the yeast behave with respect to flocculation and their ability continue functioning as alcohol level increased. There are lots of variables here and that is why the manufacturer would have to pick some nominal set of conditions so that the results compare based on the properties of the yeasts themselves, (flocculation, alcohol tolerance...) and not on the conditions in the lab. But naturally, for these data to be useful to the brewer, the test conditions would have to be typical of the conditions found in the brewer's fermenter. All in all these numbers should be used only as a guide. If you prepare a 1.050 wort and ferment it with a strain rated at 75 - 80% attenuation you would expect that your final SG would fall in the range of 1.0100 - 1.0125. If it ends up at 1.020 then you would look for some cause (insufficient pitching rate, mash temperature too high, insufficient oxygen etc.) that might be responsible. Final note: a saccharification rest at 148 F would be expected to produce a more fermentable (higher attenuation) wort than one mashed at say 154 F. A. J. Return to table of contents
Date: Fri, 11 Sep 2009 09:35:46 -0400 From: Kai Troester <kai at braukaiser.com> Subject: Re: Attenuation Kevin, > I find attenuation ratings on a yeast strain confusing and I'm hoping > someone can explain it to me. Assuming the wort was mashed for a low > attenuation (say mashed at 148F) and the starting gravity was 1066. A > Munich Lager is used with an approx. attenuation rating of 75% (77% max). I > would end up around 1016 as a FG right (assuming correct aeration, nutrients > etc.)? But what determines this attenuation range on the package? Wouldn't > the yeast keep going until the fermentables were gone or the alcohol got too > high for the yeast? Why is it limited as per the strain rating? The attenuation numbers listed with the yeast strain are pretty useless and I wish they would not give them. Not only is there no standard in determining them, they also heavily depend on wort composition. I'd like yeast data that shows how good of an attenuator a given yeast strain is and how close to the attenuation limit (i.e. fermentability) of the produced wort a particular yeast will get in an average fermentation. Most of my thoughts about attenuation have been summarized in this article which is intended to answer the questions that you have: http://braukaiser.com/wiki/index.php?title=Understanding_Attenuation To illustrate the idea of the attenuation limit and that all yeasts can reach is it I one fermented samples of the same wort with a lager yeast (WY2206) and an English Ale yeast (WLP002) in fast ferment test conditions. This means warm, high pitch rate and occasional agitation. They both finished at the same gravity. This means that even an English Ale yest can be a good attenuator. But we don't necessarily want this to happen in our beers since the residual fermentable sugars that this yeast leaves behind by giving up early contribute to the character and balance of that style of beer. Kai Return to table of contents
Date: Fri, 11 Sep 2009 18:08:49 -0400 From: "RJ" <wortsup at metrocast.net> Subject: RE: Attenuation Kevin, Check out this web page at WhiteLabs http://www.whitelabs.com/beer/homebrew_terms.html Hope that helps RJ Return to table of contents
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