I've pretty much settled the protocols for mashing, sanitising, yeast maintenance, and bottle conditioning. Generally my beers come out decent. With one exception, anything that uses roasted barley.
If I use roasted barley, a ready beer is usually quite good in the first 1-2 weeks after usual period of bottle conditioning (7-12 days). When age of that beer approaches 1.5 months, bottles turn to gushers. I don't taste any off-flavours that would hint of infection, however, overall beer tastes more acrid/sharp/bitter than when it was fresh.
Here's what I tried to fix it: 1. Use fresh yeast, or use a different strain. So far I tried WY London Ale (few varieties), WY West Yorkshire, WY San Diego Super, Mangrove Jacks M44. 2. Mash longer. Temperatures tried were int the range 66-69C. 3. Ferment longer. Raise the yeast from sediment by rocking the fermenter. Raise fermentation temperature after 1-2 weeks, to help the yeast to finish. 4. Mash without roasted barley, and add a "cold brew" of roasted barley at the end of boil. 5. Adding 10-20% less priming sugar.
None of those fixes actually helped. Oh, and btw, I did't dry hop any, so hop creep is not a factor, too.
I start to think that roasted barley may provide sugars that are fermentable on a few months timeline, rather than few weeks, but was so far unable to read anything about it.
Any commends on what else I might be missing?