When doing the traditional method of mashing the method is to recirculate the first runnings back through the grain bed to filter out the debris. When I do BIAB I notice that there is A LOT of debris in the wort as I am boiling it. I assume there is far more than the traditional method since the bag is letting much more grain debris into the wort. Is this a problem? Is there any way to make the wort more clean before the boil? I have done only 3 all grain, BIAB brews so far and I use the Irish Moss to clarify. I seem to get way more of a trub layer than if I do an extract batch. Like maybe almost 2 inches at the bottom. If I leave ALL the trub in the wort instead of trying to siphon to the fermenter and leave the trub behind, will this cause problems with the fermentation and the final product?
BIAB calls for a finer crush which does result in more fine grain material in the wort.
What type of bag are you using? Try getting a bag made from a fabric called Voile. It will help keep most of the fine particles out of the wort. Vendors for custom bags can be found online.
The particles don’t necessarily hurt your beer, there’s a chance that they might contribute to a grainy/harsh/astringent flavor if a lot of husk material is included, but in general they don’t hurt.
Leaving all of the trub in the wort won’t hurt your beer, generally speaking, however, there is a chance that it contributes off flavors if it’s burned or charred or contains astringent materials. Also, just beware that you may want to rack off of that “dirty” trub sooner than if the trub were “clean”. It may also hamper yeast collection and reuse efforts.
When mashing in a bag, I mill to flour and do end up with more sediment in the wort. As long as your mash and boil pH are within the proper range, there should be no ill effects. Remember, if it was a problem, no one would do a decoction mash.