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Bugs in your grain?

Published: 19/06/2014 12:15 pm

Every now and then, we hear of brewers having difficulty with pests getting into their grains and other brewing supplies (especially over the summer months). Recently, we’ve had guys on the phone and emailing after buying large quantities of grain in bulk buys complaining about borers (“Weavils”). The larger the grain holdings, the greater the risks of having substantial losses. Undoubtedly, a little bug called the Lesser Grain Borer (known commonly & incorrectly as Weavils) is one of the most common causes of spoilage of stored malted grains. It's one of the main reasons we don't recommend over-buying, but rather buy for the next few brews only.

To put this in perspective, an initial very small population of just a few bugs hatching in stored grain can lead to a population big enough in a few weeks (Several Thousand plus their in-laws) to render an entire bag of malted barley useless over time. From that stage, once food is nearing exhaustion within the bag, the borers will eat through plastic liner bags in minutes and seek further food and breeding areas. A seriously infected bag will often have a scent similar to an ammonia smell, often described as “Mousey”.

By this point, the grain is next to useless.

The lesser grain borer has been a part of the Australian grain industry for decades now, and is common in most regions of Australia. The point of origin is actually, in most cases the farms and eggs are known to survive some malting processes as well as long term storage.

What has exacerbated the issue is under-dosing with phosphine gas in grain pits and silos when the grain has been stored, then treated. In correct doses, Phosphine is very effective, but with a single under dose, the bugs have built immunity to the effects this has.

From a small population of a dozen or so Lesser Grain Borers, within 4 months, there will be a potential population counting in the millions, such is their ability to populate a food source.

On the home brewing front, the most commonly used and reasonably effective treatment you could take is to first freeze the infected grain. This should be done in a deep freeze set as low as possible. This will initially halt the growth of the larvae, stop eggs from hatching and stop further development of immature Borers.

Flushing with CO2 is exceptionally effective though not necessarily the most cost effective for home brewers when dealing with large amounts of grain. Once the bag is inflated with the CO2, deflate it and then repeat the process. This is cost effective in smaller bags and an effective way to save grain from further damage and stop recurrence of a new generation.

Diatomaceous Earth (DE) powder can be effective in controlling free ranging populations within the grain storage area. It’s action is effective in killing off crawling Borers which may seek refuge in tight spots and cracks in flooring. A small amount sprinked/dusted on the floor and in corners around your grain storage drums helps. It works by essentially cutting the waxy coating on the bugs, sucking the bugs of moisture and systematically dehydrating them (revenge). Another way to use it is to make a thick paste with water and smear it around the inside of the container to give a good coating, then allow it to dry. A level teaspoon of DE can also be sprinkled  over the surface layer of grain in a drum and raked through the first few cm. It’s harmless to humans when a food grade version is used and actually is espoused by many as having some health benefits.

All storage containers should be thoroughly cleaned with very hot soapy water, rinsed and dried. To preveny eggs being left behind when the containers are empty and you’re ready to refill them.

Generally, the borers aren’t affected by normal surface spray insecticides such as roach or flea bombs due to the waxy coating on their body.

In store, we discard infested bags of grain to a pig farm as they arrive, since the importers and distributors tend to stick their heads in the sand and pretend the issue doesn't exist. Rather than sell it, we cop the expense and prefer to convert it to bacon. Any small hatch which may occur is swiftly dealt with through use of DE and flushing storage vessels with CO2 from our refilling station before damage is done. So far so good.

The next major problem in some areas is rats and mice.

Unless you can store all grains in metal drums, there isn’t much you can do to guarantee protection. Both rats and field mice can chew through plastic drums and boxes in short order if they so choose. The best way to control them is to have enclosed bait stations in your shed/brewing area and keep them topped up with fresh bait blocks. If handling grains which have been accessed by rats or mice, be mindful to use some sort of glove and use a dust mask. Leptospirosis/Weil’s Disease isn’t something you want to have to deal with and wild rat/mice populations are rancid with it.  Learn to like snakes &/or cats.