What to do about weevils in the grain mash

Sunday, October 25, 2020
Once my father and I were house-sitting for a time. The first morning, I got up and was delighted to see there was Coca Pops in the cupboard for breakfast.

Cocoa pops are basically puffed rice that's coated in sugary chocolate. So, I was happily eating away and was nearly done with the cereal when I looked at the bowl and noticed something odd. 

The rice was alive. 

Alive in that it appeared to be wriggling. 

Yep, the cereal had weevils all throughout it and I had eaten more than three-quarters of the bowl.

I had eaten larvae! 


It was worse than the time I found a giant weta at the bottle of a beer I had consumed... 

beer weevils

The question though is, what happens if you discover your grain mash is full of weevils? 

Can you continue to brew? 

Should you brew with old grain? 

At the end of the day, when I ate the Cocoa Pops filled with larvae, nothing happened, I was fine, the food tasted good, and so will your beer.

If you discover weevils (Sitophylus granarius) or other bugs and critters in your grain the choice is yours.

A purist may ditch the grain into the compost. 

And that's fine. 

Budget brewers who know the bugs will be killed in the boil may not have a care in the world. 

It's up to you!

pantry pest weevil

In such situations, I would personally bear in mind that grain has had weevils in it for centuries, indeed as long as beer has been brewed there have been weevils in the grain, so how big a deal is it? Indeed, it's an everyday occurrence in flour mills around the world. 

There's a tolerance level and below it, the bugs just get ground up into the mix. 

I would also consider just to what degree of infestation of moth larvae do you have? A couple here and there or is your grain bill a seething mass of writhing protein?

Any bugs in the grain will all get pasteurized in the boil so what's the problem?

The bugs should float up to the top as the water heats up, just scrape them off, relax, don't worry, and have a homebrew!

Pantry pests such as granary and rice weevils will infest and feed on whole grains and rice as well as nuts, beans, cereals, seeds and corn - so there's never been a better time to give the kitchen and brewery space a bit of a spruce up and get rid of any spills and loose items that may have fallen to the floor etc.

How do I kill weevil in my beer?

Placing the grain in a freezer for 24 hours will kill them until they are good and dead. Hopefully, you'll have some room in the freezer...

How to prevent weevils from getting into the grain?

Elimination is probably never going to be at 100 per cent. You're probably going to go for containment and thus:
  • Don't hold excess levels of grain for too long
  • Keep grain cool as larvae will hatch when it's warm
  • If you need to store grain for a period, buy it sealed
  • Keep your grain sealed in airtight containers if possible. 
  • Keep your brewing area clean. Sweep up dust & spilt grain. Give moths, weevils and other critters like mice nothing to feed on and lay on. 


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