An interesting experiment; for what it's worth, here's a fairly recent (2012) article from the Journal of the Institute of Brewing on EXACTLY this subject:
http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.2006.tb00716.x/pdf
It's CRITICALLY important to keep in mind the actual levels of turbidity / trub that they're talking about, though; "high, medium and low" are not just relative, but absolute measurable quantities. -With most home brew systems when we are careful to get low levels of trub into our fermenters we're probably much closer to large concentrations in the mega scale breweries that these studies are done in.
Having said that, they agree with a lot of your conclusions.
They agree that too clear of wort and eliminating too much trub IS actually a bad thing and particularly in the mega breweries current practices have possibly even gone too far-. -To me a huge take away is that the huge investment in a mash filter not only helps you turn over a lot of beer much faster but it also increases turbidity and that might actually be better for fermentation vs. very low lipid levels coming from lautertuns with long lautering cycles and deep filter beds.
Another statement from the article that I think is VERY applicable to homebrewers is the idea of wort lipid vs. oxygenation trade-offs and that higher level of lipids (particularly long fatty chained lipids) essentially "count" as additional oxygenation. -The yeast can directly take up these lipids rather than having to produce them from oxygen reactions.
-I also liked that the article ranked the long-chain fatty acids in terms of importance to yeast nutrition -anyone else notice that oleic acid is low in that list and listed as only being of minor importance? (This hints that olive oil is NOT a replacement for oxygen although passing more trub to your fermenter, might be.)
The document and your experiment continues to highlight what we already knew; the main points being:
- Too little trub / fatty acids in wort is bad for yeast nutrition
- More trub = faster fermentation
- too much trub is bad for stability / the beer will go stale faster
- More trub = less esters; but more higher fusol alcohols
I think when it comes to practical application, you don't want to transfer all of the trub to your fermenter but buying a trub filter and avoiding all trub is probably taking it too far unless you have a way to ensure your nutrient regime is adding enough fatty acids for yeast nutrition, too (I believe Servomyces yeast nutrient would cover us here).
Its also important to think of trub levels and oxygen levels together as one issue as the long chain fatty acids and oxygen are roughly equivalents here. Think of your "OXYTRUB" level.
If you've got too little esters and "boring" tasting ales consider the impact of trub+oxygen levels -you might want less trub / oxygen.
If you're getting burny, fusoly beers, ESPECIALLY on high gravity beers again think of your "OXYTRUB" levels (you want less trub in this case.) (My old brewery was a very simple 2 bucket electric system and I passed 100% of my trub to my fermenter; I ALWAYS got guesses that the ABV was much higher than it was and high alcohol beers always had some significant burn.)
Many home brewers who have been around a while and really looked at yeast nutrition and handling know the trade offs between pitch rate and oxygen / nutrient levels but it's really pitch rate balanced with Oxygen & Nutrient (Trub / nutrient) --Again, trub is another nutrient.
There's this Oxygen / Trub / Nutrient trifecta that we need to balance to drive the fermentation flavors that we want. (assuming that you've met the basic requirement to not have way too little or way too much trub).
The easiest way I can put it I guess is "Trub == Nutrient" so you really need to think about trub + outside nutrient levels together. Advanced brewers already know that you need to think of oxygen+nutrient together as one item and this just completes the picture.
Adam
