Calculated versus lab measured ABV and IBU.

Brewing Processes
1

I finally sent my beer away to the lab to have the real ABV and IBU values measured to compare to my calculated values.  I thought some may find it interesting.

ABV:  Calculated (refractometer/hydrometer)= 7.2%, Lab measured = 7.6%
IBU:  Calculated (BeerSmith) = 65,  Lab measured = 78

I thought the ABV discrepancy was significant but the lab told me that was actually pretty close and that a lot of commercial Brewers or farther off in this.
As far as the IBU calculation, I whirlpool at 175 and haven’t been adding any IBUs for the whirlpool hop additions, but maybe I should back-calculate and start adding a small percentage for this.  Also thinking about it, I may move my flameout additions to whirlpool since I think they’re essentially the same thing when cooling quickly to 175.

Here’s the recipe if anyone is interested.

Batch Size: 6.33 gal
Style: American IPA (14B)
Boil Size: 8.50 gal
Color: 6.2 SRM
Bitterness: 65.0 IBUs
Boil Time: 60 min
Est OG: 1.065 (15.8° P)
Est FG: 1.014 SG (3.6° )
ABV: 6.7%

Ingredients
Amount Name Type #
1 tbs Gypsum (Calcium Sulfate) (Mash 60 min)
14 lb        Pale Malt (2 Row) US (2.0 SRM)
9.6 oz Cara-Pils/Dextrine (2.0 SRM)
9.6 oz Caramel/Crystal Malt - 40L (40.0 SRM)
0.70 oz Chinook [13.0%] - Boil 60 min
0.80 oz El Dorado [15.0%] - Boil 15 min
0.45 oz Centennial [10.0%] - Boil 15 min
0.30 oz Columbus/Tomahawk/Zeus (CTZ) [15.5%] - Boil 15 min
1.            Whirlfloc Tablet (Boil 15 min)
1.00 tsp Yeast Nutrient (Boil 15 min)
0.50 oz Columbus/Tomahawk/Zeus (CTZ) [15.5%] - Boil 7 min
0.30 oz El Dorado [15.0%] - Boil 7 min
0.20 oz Centennial [10.0%] - Boil 7 min
0.80 oz Columbus/Tomahawk/Zeus (CTZ) [15.5%] - Boil 0 min
0.50 oz El Dorado [15.0%] - Boil 0 min
0.30 oz Centennial [10.0%] - Boil 0 min

At flameout, cool quickly to 175 and then whirlpool hop for 30 minutes: 1.75 oz Centennial 2.25 oz El Dorado 0.5 oz Columbus Mash 60 @ 150

starter California Ale (White Labs #WLP001)

2

.3% +/- is within the federal label requirements. Thanks for sharing

3

Thanks for posting the info. I’m not surprised by either. The abv is a crapshoot, based on the accuracy of readings and of the equipment used to take the readings. As for the IBU, there are IBUs that calculate from a cool hopstand/whirlpool like you’re doing - I just don’t perceive them @ 175F or less, so I see them as ‘irrelevant IBU’. Good info.

4

I recently got a belgian dubbel I brewed analyzed by a lab as well (Saranac Brewing). I was rather surprised that most of my numbers were pretty much spot on for ABV, final gravity, and IBU’s. My color SRM was a bit off but only by a few, and as I understand it, that one can be pretty different even from lab to lab.

5

Really cool info, thanks for sharing