The Evil Weevil

The Necessary Weevil - as John called it! Harmless as they may be, it can be irritating to see a bunch of them crawling out of my grain sack. I'm not sure if there is empirical evidence, but it does also make sense to hazard a guess that if the infection were to be bad enough, it may even affect brewing efficiency?



So far I've been having really good results trying to repel them by putting whole garlic cloves into the grains. Upon opening the grain containers, there's definitely a garlicky smell to it, but it's (so far) not discernable in any of my beers. The garlic does need regular replacing though, as it tends to shrivel and dry out every couple of months or so.

So is there evidence for such practices? Perhaps we could do a little literature searching to support or improve weevil-repellant techniques ...

This piece of work by a Malaysian group used various essential oils and extracts to test their efficacy against rice weevils. The group found that cinnamon and ginger had the highest repellency, while lemongrass showed no effect. Turmeric and black pepper had moderate effects.

Looking at some similar papers, it seems that cinnamon consistently showed the highest efficacy against weevils.  Do note, however, that they used the true cinnamon (C.aromaticum) as compared to the more commonly-available cinnamon cassia (C.cassia). The latter should still work, however, if we were to assume that the repellent effects are due to the presence of cinnamyldehyde. 

Anyway, I've replaced most of my garlic with a sachet containing a collection of cinnamon cassia bark, clove buds and black pepper - all easily available at the local dried food store. Let's see if works!