Brew #2: White House Honey Porter

Just in time for our next brew, the Internet brought to my attention the fact the White House had released its own homebrew recipes. The recipes looked pretty simple, and the video showed that they were using the same basic kit we were. We decided the porter would fit nicely with the cold, dark winter.

Recipe: Here's the PDF. Lots of grains and malt extract, vaguely specified hops, a pound of honey, and Nottingham yeast.

Feedback: Everyone loved it. "Seriously, this is one of the best beers I've ever had." -- a friend. By my calculations the alcohol content was around 6%, but empirically it seemed stronger than that. I would normally split a bottle with my wife in the evening.

Let's learn about: ABV

How did we calculate the alcohol content? With science.

The density of dissolved sugar is greater than that of pure water. We measure the ratio between the densities of the liquid in question (our brew) and water as the specific gravity (SG), using a hydrometer, which is basically a weighted buoy with tick marks. The deeper the hydrometer sinks into the liquid, the lower the liquid's specific gravity.


Yeast converts sugars (sucrose, fructose and glucose, mainly) into ethyl alcohol and carbon dioxide gas. Because the gas bubbles off through the airlock and the remaining ethyl alcohol is lighter than the original sugar, the SG of the brew decreases during fermentation, approaching that of pure water (1.0).

So, we can calculate the amount of alcohol produced during fermentation by comparing the SG measured before fermentation (original gravity, OG) to that of the finished product (final gravity, FG). Subtract the FG from the OG to get a number indicating the amount of sugar that was fermented, and multiply by a magic constant to convert the units to percent alcohol by volume (ABV). The formula is:

%ABV = 131.25 * (OG - FG)

For this brew, I measured OG=1.064 and FG=1.020, for a difference of 0.044. So the alcohol content was 131.25 * 0.044 = 5.775 % ABV.