A few weeks ago my Naked Porter, so named because it’s the Dry Dock’s Vanilla Porter sans vanilla, was fine. Now nearly every bottle I open gushes. I got one that was positively nasty with bad fermentation by-products. The rest have been overcarbonated but not bad. Here’s one:
Finding out what could have happened is a bit of a forensic effort. The bad one was a true gusher and there was no doubt that it was not a good beer. The rest are tart with some diacetyl but that was always present. Diagnosing the beer is made more difficult by the fact that it’s the one batch I’ve made that I didn’t keep notes. There are no off aromas. The beer has always been opaque so it’s hard to tell if there’s any significant cloudiness. When I poured, the beer appears to be clear. Aside from the one truly bad beer, the beer is not gushing in the glass. Its head is persistent but not growing. Based on this, I have to assume I had the one bad bottle from the batch, likely the result of a dirty bottle and not any brewing error.
Now I’m working from memory. It’s a very dark beer with lots of roasted malts, leading to a highly acidic mash. I added some calcium carbonate – chalk – to the mash to bring the pH up. Later, reading the Brewing Elements series book “Water”, I learned that the chalk does indeed dissolve in the acid environment of a mash, then combines with phosphates to form apatite chrystals. In beer, these form condensation nuclei, sites where bubbles can form, much like bubbles in a normal beer form at minute scratches, imperfections and dirt specks on the glass. Beer is a supersaturated solution of carbon dioxide so when the pressure is released with condensation nuclei present, the beer gushes.
Our water requires treatment for very light and very dark beers to control the mash pH. Chalk is ineffective and leads to problems as mentioned above. Next time I’m brewing very dark, I’ll add sodium bicarbonate, baking soda, instead. It’s soluble and controls the pH much more effectively. Yes, I’m adding sodium but our water is so low in sodium that it shouldn’t matter.
So I have good tasting gushers. So be it, I learned a valuable lesson from it and I had no plans to enter any of these over-the-top coffee bombs in any competition. I’ll enjoy them at home, share them with understanding friends and will not make the same mistake again.