We've been having some issues with diacetyl reduction in recent kettle sours. We have been CIPing our kettle thoroughly, purging with an obscene amount of CO2 while cooling the wort, and we get very clean-tasting sour wort at knock out ot the fermenter. We knock out the wort at 3.25-3.4 pH, oxygenate as normal, and ferment at 68-70F with our house ale yeast (Wyeast 1728 - Scottish Ale). We tend to get pretty rapid attenuation, similar to our non kettle-soured beers. But even after a 5-7 day diacetyl rest at 70+ degrees, our force D test is positive. We've experimented with different sources and strains of lacto - no change. On our last batch, once we reached terminal gravity, we dumped the yeast and pitched some fresh, active yeast from another tank...our hypothesis being that the original yeast was too stressed out after low-pH fermentation to reabsorb all of the diacetyl, and that a fresh pitch would be able to get to the finish line. But alas, there is still a small amount of diacetyl.
We are considering buying some more pH-tolerant white wine yeast (one that will not kill the sach) in hopes that it will be able to complete the fermentation and absorb the diacetyl.
If anyone has had similar experiences or has more knowledge of low pH fermentations or diacetyl-destroying yeast strains, we'd love to get some input. I'm about ready to abandon kettle souring and stick to mixed fermentation with brett, and longer aging.
We are considering buying some more pH-tolerant white wine yeast (one that will not kill the sach) in hopes that it will be able to complete the fermentation and absorb the diacetyl.
If anyone has had similar experiences or has more knowledge of low pH fermentations or diacetyl-destroying yeast strains, we'd love to get some input. I'm about ready to abandon kettle souring and stick to mixed fermentation with brett, and longer aging.
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