The issue isn’t that bugs get in, but that bugs are already in. Weevils will lay their eggs in with the flour, which are impossible to sift out. Unless you bake them at 140°F/60°C, freeze them at 0°F/-18°C, use pesticides, or deprive them of oxygen, they’ll eventually hatch and eat your flour/grain.

Hah, for once, a benefit of having celiac, no wheat for me apparently means no weevils for me. I mix up a lot of gluten-free flour mix to substitute for all-purpose flour. It's a mix of way too many flours and starches (white rice, brown rice, sweet rice, potato starch, potato flour, ivory teff, tapioca starch, arrowroot flour) that I got from a blog many years ago, and haven't tried to slim down because it works great for me. Never had any bug issues; maybe specialty flours have better quality control.

maybe the tapioca is toxic enough to kill the bugs

what proportions do you use

I mix up 2 kilograms at a time: 500 grams sweet rice flour, 400 grams brown rice flour & potato starch, 200 grams ivory teff & arrowroot starch, 100 grams white rice flour, potato flour, & tapioca starch. The original recipe had almond flour instead of white rice flour, but I decided to make this nut-free (had some friends with nut allergies).

thanks, this is great info! it seems like you have some premixed starch mixes as ingredients?

Nope - those are all bagged single ingredients I usually order online. Authentic Foods has most of them. The ivory teff is from Maskal. The arrowroot and tapioca might be called flour, starch, or powder - all the same thing. Potato starch and potato flour are 2 different things.

oh, so for example it's 100 grams white rice flour, 100 grams potato flour, and 100 grams tapioca starch, not 100 grams of a mix of the three? i guess that makes it add up to 2 kg

Yep, that's what I meant.

thanks! should have been obvious, but to me it wasn't

yes but see https://news.ycombinator.com/item?id=36048781