Rich C's Page

This must be incredibly frustrating and disappointing for you, particularly with your previous history of over 50 brews with no problems. This previous success means you should trust your brewing process UNLESS you have changed something recently. I doubt it's a daiacytle issue which leaves very distinctive sweet buttery flavours in a beer yet unless its presence is at the extreme high end, generally still leaves a beer drinkable. Strong phenolic flavours generally indicate a fermentation issue around temperature control but your stated practice is sound ( unless your controlling unit is faulty.... reading high ) It's not likely to be a yeast issue as you have tried a an assortment and 2 sachets for 20L in my opinion is not excessive. T My money would still be focused on sanitation, as infection is the main reason for most of us having to dump a batch due to offensive off flavours and smells. How do you cool wort from boiler to fermenter? Immersion coils, counter flow and plate chillers need to be flushed and cleaned thoroughly after use.... Over time they can build up organic soils which are great hiding places for bugs. Often a strong wash with caustic is required to remove this residue...many other cleaners will not often do this. Pressure cookers are great for sterilising plate coolers, insert your immersion coil at least 15 minutes prior to end of boil and counter flow chillers need to be absolutely sterile prior to use...I recirculate boiling wort for 15 minutes through my counter flow to be sure but not all of us use pumps. If you have a sight glass in your boiler, give this a good soak and clean in caustic. Obviously all hoses in contact with wort after the boil stage also need to be absolutely clean and sterile. I was a dairy farmer for many years and elevated bacteria counts almost always were traced to a small build up of organic soils ( fats and proteins ) and this was after washing everyday with strong hot alternating caustic and acid washes. Like a swimming pool, often a concentrated caustic bomb is required to remove the problem soil / bugs that slowly can build up.
So my advice is soak everything that has contact with the beer after the boil stage ( dis-assemble valves, fittings etc) in a strong hot caustic solution, dump solution before it reaches 75C ( as soils start settling out again at lower temperatures) and follow with a good acid rinse / sanitizer. Be generous with the chemicals as you want to 'bomb" the potential problem area.
Being scrupulously clean extends obviously to yeast preparation...hydrating / culturing on stir plate etc as a yeast starter can easily be infected at an early stage, or undergo mutation. From personal experience I can confirm this!!
Just my 2 cents worth.... I really hope you quickly find the problem quickly!