I use the BIAB method. My keggle has a side drain valve with a pickup tube going to the bottom. After the boil, I get gobs of fine material coming through my counter-flow chiller into the fermenter. It must be mostly fine crush flour leaking out of the brew bag during the mash (I use hop sacks in the boil).

I bought some #60 screen (250 micron) and did a shake test on my grain to see what is in there. It looks like maybe 5-10% of the crush is fine enough to go through the screen and my brew bag since they are about the same mesh size. The bag drains like a champ when I pull it, so I don't really want to change to muslin or something else.

Question for the group: Is there a disadvantage to screening my grain to remove the flour before mashing? Obviously I have to make up for missing material in the grain bill, but the $3 more is worth it considering the hassle I seem to have with excess trub and chiller clogs at the end of the run.

1 Answer 1


'Is there a disadvantage to screening my grain to remove the flour before mashing?'

Aside from your point about losing extract (the most important thing, really), a few things I can think of:

  • Fine flour disproportionately represents potential extract, by weight. "Fine grits and flour [...] yield some 50-60 % of the weight of milled malt but 80-90% of the extract" (source). So if you lose 7% by weight in fine flour by sieving it, you'd have to add more than 7% more grain to get the same OG.
  • Fine milling of husks and under-modified parts of the malt increase extraction of tannins (which can impart astringency) and beta-glucans (which can screw with wort separation), respectively. Quite the opposite of a disadvantage, it might actually make for a cleaner beer and a more fluid process.
  • Changing the ratio of fine flour (mostly starch) to husk by sieving may alter the balance of flavors in the resulting wort, favoring more husk-y flavors per unit of extract.

I'd say try it, see if it makes a difference, and if it makes your process easier and still makes good beer, that's all that matters.

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