I haven’t posted here in a while because I’ve not been brewing lately, but I’ve still been very immersed in the local beer scene. It’s been a busy summer as Festival Coordinator for the Oregon Brew Crew and I’m about 2 months into my new job as a Quality Analyst at Portland Brewing/Pyramid Breweries. So I’m now actually a member of the industry!
The QA lab at Portland Brewing gives me access to a wide array of equipment and I’m learning a lot about brewing and beer chemistry. One of the perks is that I’m allowed (heck, encouraged) to bring in my own homebrew to run tests on. The results have been very interesting and I thought they might be worth sharing with the rest of my homebrewing friends.
I brought in three of my beers to test and I was hoping to discern some patterns or trends, but it looks like I can only paint in very broad strokes. Not surprising that there is a lot of batch to batch variations in doing stove top small batch homebrews.
*One major caveat to these tests is that the samples I brought in were all fairly old and no longer drinkable so I didn’t feel bad dumping a couple bottles to do the tests. I don’t believe it should affect data like IBUs and color but I could be wrong. Along with oxidation there could be some evaporation of alcohol, but the ABVs on all three were higher than I expected to begin with, more on that later.
The first result is that my measured IBUs are way lower than the BeerSmith estimate. That’s not a complete surprised since calculated IBUs is just an estimate based on X% alpha acid hop in the boil for X amount of time, but the amounts they dropped were a bit shocking. My experimental hop IPA was estimated at 81 IBU and measured at 30.5 IBU, a drop of 62%. My porter was estimated at 31 IBU and measured at 18.5, a drop of 40% and lastly my california common was estimated at 35 IBU and measured at 17.5 a drop of 50%. I’m not sure those are close enough to derive a trend from, but the average is about half. Another thing I’ve learned at the brewery is that IBUs in the wort (which I assume the BeerSmith estimate is, immediately after the boil) will drop during fermentation since the yeast will eat up some of the alpha and beta acids from the hops. I didn’t know that. Even in our commercial beers we see the IBUs drop.
The ABV (alcohol by volume) on the other hand, has been higher than expected, and by a pretty large margin. I realized that I was making a mistake checking my final gravity by not letting the CO2 out of solution before I measure, which lowers the density of the solution and floats the hydrometer a bit more, so I know my FG readings are off, but these are old samples so there’s nothing to be done about it now. My experimental IPA was estimated at 5.8% and measured at 6.68%, a whopping 15% increase. My porter was estimated at 4.7% and measured at 6.0%, a 27% increase. My california common was estimated at 4.6% and measured at 5.4%, an increase of 17%. If I change the measured final gravity in BeerSmith to what I measured, then the measured ABV jumps up to 5.4 on the Common, so the estimate in BeerSmith is dead on, I was simply measuring the final gravity incorrectly, so that solves that mystery.
The SRM (color) for all three beers was also darker than the estimate. This is somewhat expected, since I’ve read and been told that beers brewed with extract will be darker than their all grain counterparts.
So there we have it. Some interesting numbers from doing actual wet chemistry testing on beer rather than relying on estimates and formulas. Of course, the downside is you can only test after the fact, so you have to adjust your recipe for the next batch rather than the one you’re currently working on.