during mash. if grain bed gets locked there is not a whole lot of water surrounding the grist to encapsulate it. when the recirc bypasses it all the ratio is not great.Channeling during mash recirc or sparging? Channeling during the mash is much less of an issue than during a sparge. Recirc during mashing is primarily for temperature stability. You don't need recirculation to get conversion during the mash - just water surrounding the grain grits and a suitable temperature.
Brew on
like making pasta and not getting the noodles to free flow, in this case it would be the pasta getting stuck together and locked up, the center pieces will become uncooked.