Friday, February 19, 2010


It is only been recently that I've been measuring my original gravities (OG) and final gravities (FG) of my beers. So, if you look at most of the SheppyBrew Nano-Brewery recipes, the listed OG's FG's and therefore alcohol by volume (ABV) are all estimated based on QBrew or Beersmith (software programs I used for formulating my recipes).

Late in 2009, I got myself a hydrometer and actually starting taking measurements. My OG's have all been close enough that I feel good about the listed estimates. Some are slightly high and some are slightly low which can be explained by imprecise measurement of ingredients. However, my FG's have all been high. This means, of course, that my yeasties have not been converting as much of the sugars as BeerSmith says they should. The result is less alcohol in my beer.

Another potential problem of low attenuation is that my beers could be overly heavy and/or too sweet. Maybe I just like a beer with body, but I have not noticed this as a problem. All my beers I've tasted since I've been taking hydrometer readings have been what I would categorize as great beers.

But, I would sort of like to get my FG's down closer to the range that seem to be typical. Usually software and recipe books that list attenuation seem to indicate right around a 74% attenuation is what I should expect for the yeasts that I typically use.

So far I've taken readings on:
Phat & Tyred1.0561.01769.6%1.015
Blackhawk Black1.0611.02067.2%1.016
Tweedle Beetle Stout1.0891.02670.9%1.023
Leprechaun Stout1.0561.02064.3%1.015
Fools Gold1.0601.01771.7%1.016
Where OG = Measured OG; FG = Measured FG; AA = Apparent Attenuation; Est FG = Target FG (estimated based on 74% attenuation).

So, all my attenuation numbers are low compared to what my yeasties should be able to get Those yeasties are either consistently over-stating their abilities, or something in my process is preventing them from performing to the best of their abilities. Since all my batches are Mr. Beer sized ... less than half a typical packet of yeast is designed for, I obviously am pitching plenty of yeast to do the job.

So, why are my yeasties under-attenuating? Well, I suppose one thing I should do is review my measurement accuracy. Perhaps I should even check the calibration of the hydrometer, because I never have checked to make sure that distilled water at 60 degrees actually comes up with a specific gravity of 1. My hydrometer is not the most precise piece of equipment and I do not always pay real close attention to my measurements. But, for now, lets assume that I am measuring the specific gravities correctly.

One thing I have been doing recently is making sure I aerate my wort better before and after pitching the yeast so that the little yeasties have more oxygen to work with. I started doing this with Leprechaun Stout which is my worst attenuation so far.

I've also started to add just a bit of simple sugar (regular white table sugar) to each recipe. I started that with Fools Gold. While that is my best attenuated beer so far, it is still not quite where I want to be.

My last couple of batches (Quarter Life Crisis and Brother Bear Dopplebock), I've really paid attention to fully hydrating the dry yeast before pitching. Neither of those are done fermenting, yet, so I do not know how their FG will turn out.

I do tend to ferment towards the low side of the suggested temperature range for most of my beers, and until Brother Bear Dopplebock, I have not really been monitoring temperature as closely as maybe I should. So, it is possible my yeasts are getting close to the end of the fermentation and the temp is just swinging out of their comfort range for them to finish up completely. With my new monitoring technique, I will start to pay better attention to temperature swings and try to make sure my ambient temperature starts warming up right when the yeasties are thinking about finishing.

Another thing I can do on my partial mashes (Phat & Tyred, Blackhawk Black, and Quarter Life Crisis) is mash at a lower temperature for a longer time. I also need a better way to measure my mash temperature ... but that is probably a topic for another time.

Really, when it comes right down to it, if I am expecting an FG of 1.015 and I am getting 1.017, who cares? That actually is well within what I can expect a measurement error. And I am quite certain I would never be able to taste 2 beers that were exactly the same except a 2 point gravity difference and tell you which was which. So, lets not worry about Phat & Tyred or Fools Gold. I'm also not going to worry about the Tweedle Beetle Stout. Originally, I thought it was worse than it actually was because my estimated OG was lower than my measured OG, and I did not adjust my expectations based on the new higher OG. So, I was basing my expectation on 1.020, got 1.026 and thought that was pretty bad. But, I should have been comparing it to 1.023. Actually, considering that this was my first Imperial beer, I should be (and am) pretty happy with 71% attenuation on such a high starting gravity beer.

That leaves us Blackhawk Black and Leprechaun Stout. Blackhawk Black is such a fantastic tasting beer that I am removing it from the list of disappointing FG's also.

So, I guess that really leaves one beer with a disappointing final gravity. I should not be worked up about the final gravity of one beer. Especially a beer that is made out of so many ingredients I have no control over. And, truth be told, I want this beer full bodied with a bit of sweetness to compliment the peppermint, anyway. So, I guess when it comes right down to it, for this set of beers I actually have no complaints about their attenuation.

So, what was my point? Oh yeah, I want to get better attenuation out of my yeast. It is not a big deal since I am making beers that are really really great. But, I just would feel more accomplished if every once and awhile, one of my beers finished at or lower than the expected FG. Obviously, I need more data. Need to brew more beer!

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1 comment:

  1. Just wanted you to know I read that whole post. I'm glad that you like your beers.