Now I'd like to know your thoughts on the yeast floccing out after fermentation and forming a layer between the beer and trub I recon it reduces that risk of off flavours. Autolysis I think it's called. What's your thoughts on this JA?I used to try to point out that trub is yeast but it seems to have entered the homebrew vernacular as anything that's not clear wort at any stage of the process.
And I transfer it all to the fermenter so I don't worry about it, anyway.
Again, trub is yeast. The layer of stuff at the bottom of the kettle - or fermenter if you've transferred it - is protein break material and hop sludge, if you haven't used a hop bag. What happens during fermentation is that the action of yeast producing tons of CO2 makes the clumps of yeast rise and fall as the bubbles form and get released. You get the lava-lamp effect during high krausen with the protein break material being swirled up and down in the "currents". When things start to settle down, the heavy, lumpy protein material along with a few dead yeast bodies starts to fall out. It settles to the bottom while the yeast is still in suspension. The live yeast finally gets done with the sugars and starts to settle out. That's where you get the layering. Yes the yeast (trub) sits between the beer and the break material, but that has little to do with autolysis. If the beer were to age for a long time just like that, it's the yeast layer itself that would cause autolysis off flavors. The truth is, though that at homebrew volumes, autolysis off flavor is rare enough as to be mythical. I'd worry about it in a big stout that you decided to age in primary for 6 months, but that's not the common practice. In the 2-3 weeks time frame that we usually use, it's not an issue. I guess if you did a lager and never transferred and stored cold for months in the primary with all the trub (and the protein break material underneath it) you could develop some off-flavors.
Yep. We're into semantics at this point. So can we settle on this: Trub is the gunk left at the bottom of the fermentor when fermentation is finished. It'll consist of anything you put into the fermentor (hop debris, bits of grain, hot and cold break material) as well as anything generated during fermentation (dry hop bits, yeast, braunhefe, dead yeast cells, spent spices, etc.). That's always been the definition I've heard. And I agree, using the German word for "cloudy" or "murky" only muddies the water, to mix a metaphor. So let's settle on sediment. I second.
And when repitching I tend to call it cake if it's the whole mess and slurry if I've done anything to separate the yeast form the rest of the gunk. I don't use the word trub much. And don't even get me started on pronunciation...traditionalists insist on calling it "troob" where as most homebrewers, non-German speakers, at least, tend to go with the more phonetic way of saying it. 
Semantic arguments are so fun.
Great find and an interesting read and for the most part, substantiating what most of us have been saying. Look at me
But as I said earlier, my wife has to take credit for why we “dump it all in”.
) affect the new brew or is basically inert and flavourless?
I do it all the time. Yes, it's an over-pitch but that won't hurt most beers. Most often, I'll brew a relatively low-gravity beer, rack off when it's through primary and put a new batch of higher OG beer right on top of the cake. You better have a big fermenting vessel and have a blow-off tube at the ready, though because it'll take off like a rocket and krausen like crazy. Pitch a little cooler than you might otherwise an you can control the vigor of the fermentation.
