Attenuation Question

[Westco]

So I just brewed my second lager of all times and I very proud that both of my lagers actually came out decent. On this last lager i have been trying to figure out my attenuation % so that I can see if I am fermenting well or not.

According to my brew calc I had App atten of 77% and Real Att of 63.1% (you can check theses numbers yourself I had a SG of 1.054 and a FG of 1.012)

What I need to know is what is the difference? When another brewer asks me whats my attenuation do they usually want the real or the App. Also when I look at a yeast strain like the one I used which is a 2308 wyeast Munich lager strain it says that the attenuation is 70-74%. How do i know if that is real attenuation or not?


I am very confused as I can't tell if I actually hit my numbers correctly or not. I can't tell if my fermentation is complete or not. With a SG at 1.054 and a FG at 1.012 reading the App. Attenuation it seems that I have fermented well over the range of the yeast strain. But if I look at the Real attenuation it shows that I could ferment out a few more % points. I hope my question makes sense

Math was never my cup of tea.

[Big Tex]

Generally, apparent attenuation is what everyone uses.

John Palmer's How to Brew book has a nice section on the difference between actual and apparent attenuation. Instead of quoting his book, I would just turn to page 62.

[BDawg]

Generally, apparent attenuation is what everyone uses.

John Palmer's How to Brew book has a nice section on the difference between actual and apparent attenuation. Instead of quoting his book, I would just turn to page 62.

+1

[Dirk McLargeHuge]

Generally, apparent attenuation is what everyone uses.

John Palmer's How to Brew book has a nice section on the difference between actual and apparent attenuation. Instead of quoting his book, I would just turn to page 62.

Or read it here: http://howtobrew.com/section1/chapter6-1.html

[ajdelange]

When homebrewers are talking to one another the apparent degree of fermentation (ADF) is nearly always the measure being referred to. If the numbers are in the range of say 65 - 85% then you can be sure that it is ADF that is being discussed. The real degree of fermentation (RDF) is the amount of extract consumed by the fermenting yeast and thus has real physical meaning. If the original extract in the beer is OE and the extract remaining after fermentation is TE (called the "true extract") then the RDF is 100 x (OE - TE)/OE. Determining the TE requires removing the alcohol from the beer by evaporation down to about 33% of the original volume then making back up to 100% volume with DI water and measurment of the specific gravity. TE = °P x (SG_reconstituted beer/SG_beer) where °P is the degrees Plato corresponding to the specific gravity of the reconsitituted beer. OE, which is also in °P, represents the number of grams extract per 100 grams wort. TE represents the number of grams of extract remaining in 100 grams of fermented beer.

The ADF is simply 100 x (OE - AE)/OE where AE is the apparent extract which is the number of °P corresponding to the final gravity of the beer. It does not represent the true extract of the finished beer because of the effects of alcohol on the hydrometer reading. OE and AE are both in °P but most homebrewers don't want to be bothered with the additional complexities of interconversion between SG and Plato though many hydrometers for homebrewing use are marked in Plato (or the nearly equivalent Brix), and so simply use the "specific gravity points" (1.040 SG equates to 40 points) in the ADF formula. Differences between ADF calculated with points and °P are usually small (smaller than the errors in hydrometer reading and from change in OG during fermentation).

You can't know the RDF without doing the evaporation bit but you can estimate it from the ADF by

RDF = 3.27 + 0.766 x ADF

which is based on 30 beers I've measured (if you are statistically inclined, r = 0.98 for these data). So for 77% ADF you would estimate RDF at 59%. How did you calculate 63% (just curious)?

Estimating RDF is useful because from it you can calculate TE and from that an estimate of the caloric content of the beer though often this is information that you might be happier not knowing!

[Westco]

[quote=
Math was never my cup of tea.[/quote]



Ok so that is good news Ill just go with App attenuation. Given those numbers it still looks like I hit the fermentation just right and that's what I care about most. Thanks for your help

[Hoppy Brewah]

I have noticed a huge difference in sweetness from 1.010 vs 1.014, which is the range that most of my beers finish around. Obviously it depends on the style, recipe, and balance of other ingredients, but 1.010 is generally very dry and 1.014 is much sweeter. I made a Belgian Amber Ale with the Antwerp Ale Yeast (WLP 515) and mashed at 150 and it finished at 1.010 - too dry for the recipe's bitterness. I also fermented the same batch with Cal Ale Yeast and it finished at 1.012 and had a nice balance of hop bitterness and residual sweetness. ADF is a good measurement, but final gravity will determine the taste and balance of the beer.

[ajdelange]

I have noticed a huge difference in sweetness from 1.010 vs 1.014, which is the range that most of my beers finish around. Obviously it depends on the style, recipe, and balance of other ingredients, but 1.010 is generally very dry and 1.014 is much sweeter.

Huge? You taste what you taste but 1.010 corresponds to an approximate true extract of 4.5 °P and 1.014 to about 5.6 °P i.e. a 1.014 beer contains a bit less than 25% more sugar than a 1.010 one.

OTOH the last 2 beers I brewed finished at respectively 1.011 and 1.013 but both have true extracts corresponding to 1.020 and thus taste just about the same WRT sweetness.

I guess that with all the variables, differences in palate and so on the bottom line is: YMMV