In back-to-back beers, using different yeast, I’ve had krausen reach the top of a 6.5 gal carboy, with the beer line at the 5.25 - 5.5 gal mark. I’ve brewed 12-15 batches this year, and I can think of maybe only one other time this has happened. Is this normal? Will the same yeast strain produce totally different krausens, all else held constant? Is this a sign of pitching enough yeast with enough oxygen? Or is this a sign of something else?
The first instance was a 1.058 OG red ale with wyeast 1056, kept at 64F using a thermowell*. I actually had to use a blowoff tube for the first time ever, even though this isn’t my first time with 1056. The mug of starsan into which the blowoff tube was placed also eventually overflowed, much to my chagrin.
The second instance was a 1.100 OG imperial stout with wyeast 1986, kept at 66F using a thermowell. I thought this one was, at first, going to be normal: I had maybe 2-3" of krausen after 18-24 hours, but sometime after the 36-hour mark, I returned to find the krausen caked so thickly right up to the neck, it’s impossible to see the liquid surface. I didn’t have to use a blowoff tube, though it looked like it was a close one.
As a counter-example, I recently made two extract-batches (otherwise, I’m all AG) using Surly Furious kits I’d received. I used Wyeast 1335 for that. The second kit was pitched onto a large quantity of washed slurry from the first kit, but neither had much more than 1-1.5" krausen. If I would have guessed, repitching slurry should have resulted in explosive fermentation…
I use yeast nutrient, but sporadically… not sure if this could be a cause. I also oxygenate, and for these two beers, I extended my oxygenation time using my O2 tank & stone. I bubbled in O2 for about three-four times as long as usual (90-120 seconds, with 30 seconds being the usual) for the first instance, and perhaps only two-three times as long as usual for the second instance.
*The stick-on liquid crystal thermometer on the side of the fermenter is accurate-enough to tell me that my temp controller reading is accurate.