I’m doing a Marzen (late in the year, I know). My primary fermentation went fast - 10 days at 56F, gravity around 1.02, then did diacetyl rest for about 4 days at 63F, before starting to drop slowly drop temperature for cold crash.
Stupidly, i didnt taste before cold crashing, but i have just tasted after crashing and did a quasi forced diacetyl test (let a small bit warm up to room temp in my cup). I’m detecting caramel like scent and taste.
what should i do now? Ive read about krausening to correct this, but am worried about not having enough time to lager, to have the beer ready for mid/late september (6-7 weeks from now).
Diacetyl tastes like butter/buttered popcorn. If you are tasting actual caramel flavor, then it’s not diacetyl. Probably just flavor from the malt. Did you use a crystal malt?
There’s a molecule that’s structurally almost identical to diacetyl, and has a precursor made from the same biochemical pathway, that presents as butterscotch/toffee. It’s called 2,3-pentanedione. (Diacetyl is 2,3-butanedione. The former has an extra carbon on it).
It’s possible you are tasting this, however if 2,3-pentanedione formed to the point where it’s tastable, this would almost certainly mean that diacetyl is also present. And since diacetyl has a lower taste threshold, you’d be primarily tasting butter. The fact that you are not points to this “off flavor” being simply a malt flavor, likely from the caramunich.
If you have diacetyl, the yeast will eat it all within the bottles or the keg over the course of about 3 weeks, especially if kept warmish in the 60s F or upper teens Celsius. If it’s diacetyl, it will fade away after about 3 weeks.
If it’s actual caramel from the CaraMunich, then of course it will NOT fade away after 3 weeks.
Be patient and see what happens. Don’t keep it cold. Keep it warmish. This allows the yeast to do all sorts of cleanup. I would argue that “lagering” happens even faster warm than cold. Seems weird but it’s my current hypothesis.
The first thing I would do is get a second opinion from someone with an experienced palate (a pro brewer? folks in a brew club?) about whether the beer in fact has diacetyl. Otherwise you might be trying to solve a problem you never had.
If it is diacetyl, the warm-it-and-wait approach is the simplest and least invasive potential solution. It’s worth a try. However, it also probably won’t work. If the yeast couldn’t clear the diacetyl while at high krausen/max cell density, it means they were in poor health. Then they went dormant and settled. The relatively few cells still in suspension are from the same pitch, and so they are also in poor health, and also dormant. Unclear to me why these few cells would be able to clear the diacetyl when trillions more of them couldn’t. Rousing the yeast simply stirs up dormant yeast–the same yeast that couldn’t get the job done in the first place–and they will simply resettle.
And the yeast won’t come out of dormancy simply to uptake diacetyl. Yeast don’t actually eat diacetyl, it is not an energy or carbon source like simple sugars are.
I’m not sure if the enzyme ALDC would work if diacetyl has already formed. ALDC targets alpha-acetolactate, the precursor, not diacetyl directly.
Krausening works, but it’s critical to keep out oxygen. Otherwise you might be trading one off flavor for another–namely, acetaldehyde, which forms when oxygen reacts with ethanol.
Again though, I suggest getting independent confirmation you have diacetyl before going to too much trouble.
Even if it is diacetyl though, krausening could eat another week or two, which gets tight if September’s a hard deadline. Worth figuring out how flexible that timeline actually is before you commit to a fix.
If it’s actually diacetyl, yeast basically goes dormant at cold crash temps—they can’t be cleaning it up down there. You’d need to warm back up for a few days to let them finish. But honestly you might just be tasting the Caramunich and stressing for nothing.