Originally Posted by Got Trub?
100% is only possible in the laboratory.
100% conversion efficiency is certainly possible but you may have to work for it by either milling really fine (which may cause you to spend the whole day lautering) or use a decoction schedule during which all or almost all the grain is boiled.
I was just listening to one of Jamil's podcasts where he discussed not trying to get much > 70% efficiency to avoid extracting undesirable flavours. It was either the Kolsch or the Dusseldorf Alt podcast.
Now what Jamil is talking about here is the efficiency into the kettle. This includes lautering losses and I agree with him that you need to leave some efficiency behind at this stage for wort quality sake. I don't agree with his 70% though and for me that number is more like 80-85%.
But what needs to be taken into account here is how did you get the 70%:
I can have a very poor conversion efficiency of 75% and excessive lautering with an efficiency of 93%. The combined efficiency is 70% but the intensive lauter may have caused oversparging. Or I can have a very good conversion efficiency of 93% or more and a very relaxed lauter with an efficiency of 75% (this can easily achieved with no-sparge) which will produce a very high quality wort. If you ask me I'll take the latter of the two options.
I get my 80-85% from aiming for a conversion efficiency of 95%. I then need a lauter efficiency of 84-89% which can easily be achieved with a 2 run-off batch sparge and only 15% boil off.