Fri Feb 07, 2014 11:31 am
Thought I would go ahead and post some thoughts on this in case someone else is having similar issues and looking for answers.
The 'cup of wort in the garage' experiment that did not pH dive nearly so precipitously I think is a strong clue. Garages don't normally carry the bacteria load that parts of the home do (lack of decaying organics). So, it would be fair to conclude that the 'garage wort' got a relatively bacteria-free wild yeast innoculation and fermented fairly normally. A little lower than a cultivated S. ceravisiae yeast, but not wildly out there. So, as others have alluded to, this points to a bacterial infection somewhere post-boil. Since the finished beer here tested negative for bacteria and the pH appears to dive immediately in the fermentation lag phase, I would conclude that a bacteria is present that peacefully coexists with yeast, does it's dirty work early, and is then killed by the increasing alcohol content produced by the yeast. There are probably products in the beer that are 'off-flavors', but you may be a 'non-taster' for them.
So, these bacteria are either surviving the sanitization process or are being innoculated into the wort via something that you don't sanitize. You don't sanitize the yeast innoculation (obviously). It is known that dried yeast carry a small bacterial load. It should be so small that yeast growth should crowd them out. But it would be worthwhile to switch to a liquid yeast culture for their purity and look for resolution. If using dried yeast, rehydrate them. Non-rehydrated yeast are weak and may not crowd out bacteria like we want.
As to sanitizing, the OP has gone to mashing with RO water. So, this would indicate hard water as the home water supply. Hard water makes Star San less effective. Breweries often save lots of money on cleaning and sanitizing chemicals by using softened water for these purposes. pH is a good clue here. Star San solutions should be below pH=3.5 and not be cloudy for effectiveness. If it's not, double up on Star San (better) or use RO water for making the solution (the best). Even with all this, it might be possible, as another poster pointed out, that a bacteria has developed resistance. If fermenters are glass or plastic then the easiest solution is to switch up the pH of the sanitizer and go with an alkaline one. I go with bleach solutions as they are cheap. Again, with hard water conditions, double up or go RO.
When you've sanitized the fermenter and emptied it, turn it upside down or cover or plug the top . Dust settling out of the air in your house is loaded with nasties. They can't crawl or anything like that, but they sure can fall into stuff. Don't sanitize something like a racking cane and hose and hang it somewhere for an hour or two and think it's still sanitized. It's not. Think like this: 'it's raining dust in here', to make your sanitization issues go away.
How are you aerating? If you're not careful, this could be the introduction route. If you're using an aquarium pump and stone to aerate, use a sterile filter and consider replacing the stone often.
A good test for all this would be to boil up some DME, cool it, purge one of your sanitized fermentation vessels with CO2, drop in the cooled DME, aerate in a sanitary fashoin, and air lock it. With no yeast present, this will reveal exactly what the issue is. Look for pH drops, changes in SG, odors. If these crop within a day or two, you've got issues. Careful tasting any animals you've bred this way, some are pathogens.
BN Army // 13th Mountain Division 
