Surprisingly fast fermentation

I brewed an oatmeal stout on Sunday, and finished at around 5 PM. My efficiency was better than I had planned for (I always use an extra pound of grain), and I ended up with an OG of 1.066. I pitched a 1 L starter that I had made the day before (British Ale Yeast - LHBS was out of Irish). It was bubbling very slowly by the time I went to bed. The next morning (yesterday), it was bubbling rapidly, and by lunchtime yesterday, it was bubbling so fast that it was more like a constant stream of air. This kept up until last evening, when the krausen began to fall, and today it's mostly dissipated, and the airlock bubbles once every six seconds or so.

I am surprised by the beer finishing so quickly. An OG of 1.066 means there is a damned good amount of sugar to burn. It may have been that my higher mash temp (~156) produced far too much malty unfermentable sugar. It's also possible that my starter may have just been so ass-kicking that the yeast did their job quickly.

I'm not worried, of course. I'm just curious.

Probably a little of both, but I wouldn't think "too much" unfermentables. An oatmeal stout should be a little sweet, anyway. I always find it interesting how different yeast in different beers can act so differently.

Ahhhh, oatmeal stout - one of my favorites! I recently drank my last, and it's quickly creaping up on my to-brew list!

Lil' Sparky said:

Ahhhh, oatmeal stout - one of my favorites! I recently drank my last, and it's quickly creaping up on my to-brew list!

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Before I went all-grain, the one oatmeal stout I made was my personal best. I'm hoping this recipe turns out to be my best now that I've lost my AG viriginity. I know they're a little sweet, especially with the oatmeal in there, but this was arguably my fastest fermentation ever (incidentally, it was also my largest starter ever). I guess I'll know it a few days.

I agree, don't sweat it, fast and furious fermentation makes for great ale, IMHO.
:rockin:

That's interesting. I had a similar experience with the IPA I brewed on St. Patrick's day.

I had a vigorous starter that I harvested from a previous primary and an OG of 1.057. Like you, I saw fermentation start in 4-5 hours and was going crazy by the next day. Almost constant bubbles from the blow off. Krausen fell on Tuesday and I racked over to secondary on Thusday.

I took a SG yesterday and it was 1.008. So I bottled last night after only 4 days in the secondary fermentor.

It really made me a firm believer in pitching a high rate of yeast with an O2 rich wort!

Cookiebaggs said:

It really made me a firm believer in pitching a high rate of yeast with an O2 rich wort!

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That could be the second part: I shook the begeezus out of that thing for a good five minutes straight. I think the yeast had a lot to eat when they got in there.