Dear Mr. Wizard,

I have many back issues and couldn’t recall an article specific to my inquiry — it has to do with finding creepy crawly bugs in the grains! I was getting ready to brew one day when I discovered bugs slowly crawling out of a batch of wheat that I had just purchased. Luckily for me, I don’t grind my grains at the brew shop, but at home. I didn’t notice the bugs until a few days later when I was about to crush. What would have happened if I had ground the grains with the bugs in it and had them processed in my wort? I bring my grains up to 160 ºF (71 ºC) to steep, but not to a boil. I boil my hops in a totally separate “hop boil.” Would the steeping process at 160 ºF neutralize any live bug contamination?

Ernest Wakukawa
Kahaluu (Oahu), Hawaii

Mr. Wizard replies:

I am not entirely clear on your brewing process and will get to those pesky bugs in a moment. I am going to assume that you are an extract brewer using some grains. In this case it sounds like the pound of wheat malt was used in addition to some extract. I make this assumption because you are using the word “steep” instead of “mash” and you also mention a separate “hop boil.”

Whether an all-grain brewer, partial grain brewer or extract only brewer, the wort boiling step is extremely important. With the exception of extracts specifically designed and marketed as “no-boil,” brewers must boil their wort.

The most significant thing accomplished by wort boiling is sterilization. This step allows brewers to determine what sorts of organisms are in the wort because boiling kills nearly everything (spores can survive short boiling periods, but that is a technicality that you are not concerned with at this time) and gives us a clean slate with which to work. Of course, if we contaminate that clean slate with dirty equipment or bad yeast, that is our fault and it’s the job of the brewer to keep the wort in a clean and sanitary environment after boiling. Wort boiling also precipitates protein, isomerizes hop acids and drives off certain undesirable malt volatiles like DMS.

Insects in malt is actually a fairly common problem. I am not suggesting that this is by any means acceptable, but it is common. In my experience, flour weevils are the most commonly found bugs in malt. Weevils can cause major problems for commercial brewers if they infest a malt silo. These little critters eat malt and in the process, rob brewers of the important carbohydrates that they have purchased from the maltster. As a biproduct of metabolism, bugs, like other creatures, produce heat, carbon dioxide and water. Insect infestation — and the fecal matter that comes with it — can lead to an increase in the malt moisture content, which in turn can lead to other problems such as mold growth.

Your experience is much more mild than this and that is why I began writing about the normal wort boiling procedure. The fact is that bugs are all around us and we as humans eat lots of them. I heard on Michael Feldman’s “Whad’Ya Know” (an NPR program) that a 16-ounce jar of peanut butter can legally contain 100 bug parts. The key with anything we eat is safety. Some people intentionally eat bugs. Most intentionally eaten bugs are fried and this is an effective method of killing bacteria that may be harmful. Harmful bacteria are not killed by steeping at 160 ºF (71 ºC), but are killed during boiling.

With that said, I wouldn’t worry too much about the occasional flour weevil in the malt. Since these bugs are not rooting around in nasty environments like flies and roaches (they usually spend their entire lives in flour, malt or whatever else they are infesting), they do not fall into the “vector” bug category. A vector is something that spreads bad stuff around, like a fly that lands on your grilled Spam sandwich right after it was sunbathing on a stinky pile of . . . well you get the point.

I have seen an odd weevil in malts, as well as flour, and personally believe that a couple of weevils per pound is not a big deal. Other bugs, like roaches are totally unacceptable since they travel around and spread filth. I have also had several bags of raw wheat arrive at our brewery that had numerous insect larvae on the outside of the bags — the wheat was obviously infested. I certainly did not want to spread this problem into my storage room and destroy the rest of my grain. My malt supplier happily replaced the wheat for free. A refund should be expected for malt containing bugs and I would never buy from a shop again that refused one.

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