What to do about weevils in the grain mash

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

Cocoa Pops are basically puffed rice coated in sugary chocolate. Highly processed. Comfortingly familiar. The kind of breakfast that feels safe.

So I was happily eating away and was nearly done with the bowl when I noticed something odd.

The rice was alive.

Alive in the sense that it appeared to be wriggling.

Yep. The cereal was riddled with weevils, and I had already eaten more than three-quarters of the bowl.

I had eaten larvae.

Gross.

Worse, somehow, than the time I found a giant weta at the bottom of a beer I had already consumed.

The real question is this. 

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 that Cocoa Pops bowl full of larvae, nothing happened. I was fine. The food tasted exactly as it should. The same principle largely applies to beer.

If you discover weevils (Sitophylus granarius) or other small pantry pests in your grain, the choice is ultimately yours.

A purist might dump the lot straight into the compost.

That is a perfectly valid response.

A more pragmatic brewer may remember that insects are made of protein, fat, and chitin, all of which are harmless once heated. Anything living in the grain will be killed well before the wort reaches a rolling boil.

Historically, humans have consumed far more insects than we care to admit. Modern food safety standards allow for measurable insect fragments in flour and cereal products. It is not folklore. It is regulation.

So if a few weevils slip through the cracks, they are not introducing poison or pathogens. They are adding trace biomass that will be denatured, coagulated, and largely removed during the hot break.

It really is up to you.

It is also worth remembering that grain has had weevils for as long as grain has existed. For as long as beer has been brewed, there have been insects in the supply chain. Flour mills around the world operate with accepted tolerance levels. Below that threshold, the grain is processed anyway.

The real consideration is scale.

Are you dealing with a couple of stray larvae, or is your grain bill a seething mass of writhing protein?

Any insects present will be pasteurized during the mash and completely destroyed in the boil. As the water heats, many will float to the surface. Skim them off if you like. Relax. Do not panic. Have a homebrew.

Pantry pests such as granary and rice weevils infest whole grains, rice, nuts, beans, cereals, seeds, and corn. If you find them in your malt, there is a good chance they are elsewhere too. Consider it a prompt to give the kitchen and brewery a proper clean.

How do I kill weevils in my beer grain?

Freezing grain for 24 hours will kill adult weevils, larvae, and eggs. Low temperatures disrupt insect metabolism and halt reproduction. Always allow frozen grain to return to room temperature while sealed, to avoid condensation and moisture uptake.

How do I prevent weevils from getting into grain?

• Do not store excess grain longer than necessary. Malt is an agricultural product, not an inert ingredient. The longer it sits, the more opportunity pests have to establish themselves. Buy grain closer to brew day when possible, and only bulk-buy if you brew frequently. Extended storage also increases the risk of oxidation, moisture absorption, and flavor staling.
• Keep grain cool, as warmth accelerates egg hatching. Weevils and moth larvae thrive in warm conditions. Elevated temperatures dramatically speed up their life cycle. A cool, stable storage environment slows insect metabolism and delays egg development. Garages and sheds that heat up during summer are common problem areas.
• Buy sealed grain if storing for extended periods. Commercially sealed bags reduce exposure to airborne insects and eggs already present in your brewing space. Once opened, grain becomes vulnerable. If you plan to store grain for months rather than weeks, sealed packaging provides a critical first layer of protection.
• Use airtight containers whenever possible. Airtight storage prevents insects from entering and limits oxygen and moisture exchange. Food-grade buckets with gasket lids, sealed bins, or purpose-built grain vaults work well. Thin plastic bags or loosely clipped sacks offer little resistance to determined pantry pests.
• Keep the brewing area clean and free of spilled grain, dust, and residue. Loose grain and flour dust act as an invitation to pests. Sweep and vacuum regularly, especially around mills, storage shelves, and corners. Even small spills can sustain an infestation that later migrates into otherwise sealed containers.

Weevils are not a failure of you or your storfage abilities. They are a fact of grain. The only real question is how much you are willing to tolerate.

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How to use Sodium Percarbonate to clean and sanitize beer brewing equipment

Using Sodium Percarbonate to clean and sanitize your beer brewing equipment 

The first mantra of beer brewing goes something like this:

Make sure your equipment is clean and sanitized!

There are many ways of going about this and today we are going to discuss our preferred method which is by using sodium percarbonate.

Usually provided in powdered form, it is very soluble in water which makes it very handy for quick preparation and an easy soak of your equipment and fermenter.

This is our preferred method as it works well, it's 'no rinse' and it's very easy to order in bulk online.

If you've ever tried to buy sodium percarbonate from a specialist beer brewery shop, you'll know that you can get a small bottle or container of it that will cost you a small fortune.

If you can buy it in bulk from an online supplier, you'll do well to nab some as using it will effectively bring down your cost per brew.

How to use sodium percarbonate to clean beer equipment

Your mixing instructions are simple. To use sodium percarbonate you simply add it to water.

Be generous with it! A health scoop or spoonful is awesome.

I like to add hot or even boiling water to the fermenter drum so as to get the action of the chemical happening pretty quickly.

The boiling water also helps kill off any nasties hiding about as well.

I close the drum so the vapour gets up the sides and then when things have cooled a little bit, I give it a pretty good shake.

Watch out for hot water leaving the hole in the drum lid!

Or fill the drum all the way to the top and leave to soak overnight.

Don't confuse 'cleaning with chemicals' as 'cleaning your beer gear'

Don't confuse 'cleaning' with sodium percarbonate as cleaning your bottles and equipment or the fermenter.

For me, that is a very different process.

Your equipment needs to have as much gunk and much removed as you possibly can before you use the cleaner.

Get stuck in with a soft brush and some really hot water and make sure your fermenter is really damn well cleaned and clear of any residue from your last brew. Pro tip - you can use PBW cleaner (or make your own brewing wash!).

Giving your utensils a run around in the dishwasher never hurts as the heat kills bugs.

That line of scum that forms at the top of the water line?

You don't want to see it before you use the sodium percarbonate.

In my view, its job is the final part of the cleaning process.

Once you are ready, give your beer making gear a really long soak.

I've seen people say a quick dip of ten minutes is all you need but I say at least half an hour and frankly if I remember before brew day, I soak the inside of fermenter in the percarbonate solution overnight.

My thinking is the longer you leave it, the more bugs that will be killed, in addition to the good oxidization cleanse that will happen.

But an oxidisation clean is not sterilization right?

Fair question and a correct point.

So if percarbonate is just a cleanser, do I need to sterilize as well?

You may wish to consider using a sterilizing agent like Star San but in my experience, if you have cleaned your equipment and then soaked it very well, you shouldn't really need to use a sterilizer.

This is because the sanitizer should have killed most of the bugs, especially as there's an argument that the percarbonate does all you need to provide excellent brewing conditions.

I use this method exclusively.

The choice is yours.

If you can get cheap sterilizer and have the time, go for it.

You might already have sodium percarbonate in your laundry as a laundry soaker!

Here's a handy trick, this chemical is basically what you might know as Tide or Napisan or any product with a brand name that tries to use the word 'oxy' as in oxygen cleaning or oxidization agent. 

That's right, most of the fancy laundry soaking products have sodium percarbonate as a key ingredient!

Chances are you already have some in your home laundry so feel free to use that.
I have done so several times with no problems whatsoever!

Non scented house brands are awesome.

If you do use a scented brand, your fermenter might smell like some lovely lavender field so be wary of that and rinse with copious amounts of water if need be.

Or maybe you'll add a nice trait to your beer!

If in doubt about home cleaners, ask for the mandated information safety data sheet

If you are really worried about what's actually in your laundry soaker, you can ask your supplier for the information.

It's law in many countries that such documentation is available.

In New Zealand for instance, all such products must be registered by law and a safety data sheet be provided on demand which contains the ingredients used in the product.

You can then use that knowledge to decide if you wish to use it but we may be overthinking things a little bit here. We've never had any issues and totally recommend using laundry soakers as a cheap source of percarbonate.

So is it safe to use everyday laundry cleaner products with my beer?

If the thought of using what gets your 'whites whiter', Oxyclean or whatever Oxy style product you've found in your laundry freaks you out, take a step back and have a Kit-Kat.

These products are designed for washing clothes and yes, the percentage of sodium percarbonate is far less than buying percarbonate by itself in bulk but it works. It really works.

So why do it? 

Because it's cheap and it works.

It really does.

If you are concerned that an 'off the supermarket shelf product' will leave strange smells or residues, you can do two things:

1. You can choose to not use it and get a 100% per cent sodium percarbonate product (New Zealand brewers should check out Trade Me), or you could just rinse after the soak.

or

2. Flush your equipment and fermenter out with a lot of cold water. A trick I then do is boil the kettle and finish off the rinse with boiling water.

I'm not sure if it's a mental thing but I consider this to be the final thing that kills any lingering bugs.

I have used home brand sodium percarbonate laundry soaker products myself many times and have never had a problem.

Not once.

You could also consider using this next magical chemical: Star San

If you've ever read any internet forum about beer making and noticed that any time a keen beer brewer talks about cleaning or sterilizing, along comes a dude claiming that Star San is the best product he's ever used!?

But what is it really and is it effective?

Star San is a bactericide and fungicide. It can be used without rinsing under the proper concentrations. Star Sans' main ingredients are a blend of phosphoric acid and dodecylbenzenesulfonic acid.

That's a long way from Kansas, Dorothy!

Many beer brewers swear by this product for their kill bug killing needs, so if all the other chat about percarbonate has put you off, you might want to consider this product.

If you can't find any Star San at your local beer shop or supermarket, it may be purchased online at Amazon.

The Caustic Soda option

As an aside, if you've got say a really stubborn fermentation scum ring that just won't seem to wash off, you could consider using caustic soda.

Beer in mind that it is an extremely strong cleaning agent and it needs to be used with necessary precautions such as gloves and eye protection.

Do not get caustic soda in your eye, that agent will literally give you a chemical burn.

Believe me, when I was a young lad I worked at a chicken fast-food style restaurant and while preparing a solution of caustic soda to clean the floor, a single drop got in my eye.

It burnnned so bad.

A hospital visit and an eye patch for a week followed.

So clearly, you will need to do an excellent rinse after. Just be bloody careful.

Most beer shops or hardware stores stock the soda - it's commonly known as sodium hydroxide.

What about the sachets that came with my home brew kit. Should I just buy more of those?

Your standard home brewing kits will come with a sachet of cleaner, and it's probably advertised as no rinsing required, the so-called 'no rinse'. It is quite simply likely to be a sachet of sodium percarbonate.

Don't get sucked into buying a sachet at $1.50 a pop.

If you are going to continue to brew in the long term, like many of your ingredients, you'll want to consider buying in bulk.

What is the difference between sodium percarbonate and sodium carbonate?

A fair question.

Have you ever heard of soda ash?

This is sodium carbonate.

It is a salt made from sodium and carbonic acid. It is quite commonly used in the manufacture of glass, paper, rayon, soaps, and detergents.

Sodium percarbonate is an adduct formed from sodium carbonate and hydrogen peroxide.

One more thing, percarbonate sometimes is called sodium carbonate peroxyhydrate. As if it could get any more complicated...


Bonus tip!

You can clean your deck with oxygen bleach!

Use approx 4 litres of water and 1 cup of sodium percarbonate to clean your outdoor wooden deck. That would suit a deck size of about 10 square meters.

Bonus tip  2!

Don't confuse sodium bicarbonate for percarbonate - you're not making a cake!

So there you have it, a brief summary of how to use sodium percarbonate and the ways to buy it online, and also to find it in your home laundry.

Bonus tip 3!

Before capping your beer, check that the bottle is clean and there are no creepy crawlies hiding in the bottom... 

If you're in the United States, consider buying some sodium percarbonate from Amazon.

How to properly clean and sanitize your fermenter drum

Don't leave your spoon in the drum!

How to properly clean and sanitize your plastic beer fermenting drum after brewing a batch of yummy beer

This post will help you properly clean and sanitize your fermenter after you've finished brewing.

Note that we said both clean and sanitize.

This is because while cleanliness is next to godliness, clean is not good enough to kill and remove bugs and bacteria that may lurk in the tiny scratches of your beer fermenter.

This is basically a 'suck eggs' post - we sound like your mother telling you to clean your room but dude or dudette, you gotta clean up after yourself!

Cleaning your fermenter

It's our practice that when we have finished bottling that last beer, we clean the fermenter to remove all the scum and fermentation residue that has collected on the inside of the drum. 

If you do this now rather than in a few days or weeks or months ...it will be a much easier job.

First up, I dump what's left at the bottom of the drum on the vegetable garden as I suspect that's quite nutritious for the plants.

Then I grab the garden hose and clean the drum out.

Kill the bugs until they are dead, dead I say

Then I get a kettle of still hot and boiled water and dump it in and then I add a large spoonful of sodium percarbonate.

I then seal the drum and shake it vigorously. The heat from the boiled and sodium will act as a cleanser. 

I then drain and put the drum in a clean spot ready until I need to use it (at which point I will give it another proper dose of sanitation. 

You could use some ordinary household detergent to clean the drum but it could leave smells and residue behind. If you do choose to do this, don't use a harsh scrubbing brush as that could put tiny scratches in the fermenter.

These scratch marks could make a nice home for unfriendly bacteria so bear that in mind.

We suggest you use a clean rag. 

Or your best linen, we're not fussy. 

You could also implement a scorched earth policy and use something stronger to clean your fermenter. Caustic soda or bleach based cleaners could be used, but again I would caution on residues.

As with all chemical agents, be careful when using them and take precautions such as using eyewear and gloves.

The call to action:

If your beer fermenter has had its day in the 'beer making sun' and you need a replacement, order one online. 

We mentioned gloves - you can get boxes and boxes of them cheaply from Amazon.

Try to avoid sneaky Weta from taking a sleep in your beer bottles too....