Beer Geyser

So i was adding some adjuncts to an Imperial Stout yesterday and it foamed right up out of the keg on me. Not quite a geyser, but it was overflowing all around the rim - probably enough to put out about a gallon and a half in 15-20 seconds. I got the shop vac out and cleaned up. Looked like a baking soda volcano.

I've added stuff like this before, but never had that sort of a reaction. The additions were lactose, oak chips, nutmeg and booze (making an eggnog stout). The original batch was 10 gallons, and i had some oak cubes in booze waiting to be added to the other carboy, so i took it outside before, just in case. Went easy this time (slower add, just in case) and sure enough it foamed up but not as bad (was able to get the lid on before i lost too much).

Anybody see this before? I've done almost the exact same recipe as the 2nd keg before with no issue. My roommate thought it might be cavitation (like mentos & soda). could be the lactose too i guess? some kind of chemical reaction? The beer had been aging for ~6 months already. Some carbonation in the keg, but not really 'carbonated' (had to release some pressure when i opened it and it foamed a bit from that, but the sample i took wasn't really carbed).

sucks to lose that beer, but at least i have 8.5 gallons or so left

Yup- it's actually a physical reaction and not a chemical reaction. When your yeast create alcohol and CO2, a fair portion of it stays dissolved in the beer. When you added all those adjuncts, lactose, chips, nutmeg etc (probably the chips and anything else that was powdered and not dissolved) you created a ton of nucleation points for bubbles to form, and agitated the liquid with the dissolved CO2, so a ton of CO2 came out of suspension.

Basically a big alcoholic mentos+diet coke scenario!

I have had this happen. I chalked it up to timing and temperature adding up to unpackaged beer with an unusual amount of CO2 saturation and resulted in cavitation. Beer turned out fine.

I had that happen trying to add sugar to a vat of fermenting wine, kind of exploded everywhere. As soon as the sugar hit the liquid, boom, it went up like a volcano. The wine turned out terrible, like can't get the taste out of your mouth terrible, I'll stick to making beer. Never had it happen with beer as you described but probably the same type of thing.

indeed it's the same thing as jamming some mentos into coke. it only takes a tiny bit of dissolved gas above saturation to get that effect, which is why you can even get it in beer, wine, cider that has finished fermenting and looks totally still, but still has a little bit of super saturated CO2 remaining. it happens often when people try to add a teaspoon of pectic enzyme or tannin powder to wine or cider after it's done and looking quite dormant. boom, up it goes. the fact that yours had a little bit of carbonation meant it was totally primed for the volcanic eruption; it was at saturation until you released pressure- instantly super saturated with CO2, even though not really carbonated compared to normal beer. all you need to do next time is dissolve the sugar in a tiny bit of water, or even in some of the beer. the soaked oak chips, little bit of nutmeg, booze, these things aren't contributing, there are no serious nucleation points there to form bubbles, it's that sugar that's your culprit

Thanks for the replies. I did try and dissolve the lactose in some whiskey/rum mixture (same one i use for my regular awesome eggnog), but since i didn't want to add a liter or so of liquor it wasn't completely dissolved - there were definitely some sugar solids left. The other keg did foam up some too though (enough to that it was doing a little 'foam pillar' rising out of the top opening on the keg), but not nearly as much (it was only oak and liquor).

to prevent it in the future, can I just add *very* slowly, or do i need to shake/degass the keg a bunch before addition?

BrewRadley said:

to prevent it in the future, can I just add *very* slowly, or do i need to shake/degass the keg a bunch before addition?

Click to expand...

Either would work, but really totally dissolving would be the best bet- you should probably be boiling your sugars just a bit in some water if you're going to be adding them post fermentation. Oak chips will be less of an issue (less surface area and nucleation sites) than powders.