Vermicomposting 101: Freezing Food Waste for the Worm Bin. Is It Necessary?

Freezing food waste is a really interesting technique for managing both the quantity and the quality of the food source you are feeding your worm bin. This short article looks into 3 reasons why you should freeze food waste for vermicomposting and 2 reasons why you shouldn’t.

3 Reasons to Freeze Food Waste

Excellent way to preserve food waste for when you need it

You probably know that the worms’s capacity for processing our household waste can vary with changing temperatures, humidity, even barometric pressure for those of you “lucky” enough to have received Indian Blues instead of Red Wigglers. And you’re probably not creating the same amount of food waste each week.

Freezing household waste for a rainy day allows you to stockpile some worm food in reserve without fear of attracting odors, flies, or pests.


Frozen Food Decomposes More Quickly

Once thawed, previously frozen food will break down faster than food that hasn’t been given the “Han Solo” treatment. As our food waste is high in water content and because water expands as it freezes, freezing food waste will rupture the cell walls in your food waste.

So once the food thaws, it will decompose faster, making itself more available to your microbes and worms.

Freezing Kills Fruit Fly Larvae

It’s no surprise that fruit wastes will attract fruit flies. And certain wastes like banana peels are notoriously good hosts for tiny fruit fly larvae. This is why vermicomposters can be surprised by the presence of fruit flies that fly out of their bin when it sure seemed like fly-less waste went in.

By freezing your food waste, you can help control the introduction of fruit flies and their eggs into your worm bin.

Why Not to Freeze Food Waste

I think “wasteful” is probably too strong of a word, but expending energy to freeze food waste that you intend to feed to worms just a few days later may go against the minimalist, zero waste mindset that lots of vermicomposters admirably strive for.

The spent BTUs to freeze your waste may be considered an unnecessary step in the process that adds cost, complexity, and a greater carbon footprint.

One other issue is that thawing food waste releases water very quickly. The expansion of water as it freezes ruptures those cell walls, ultimately allowing a rapid escape of water when the food waste warms up. I am constantly pounding the table about how most vermicomposters run their worm bins way too wet.

My Thoughts: To Freeze or Not to Freeze?

I’m totally agnostic on the matter. Personally, I am a lazy vermicomposter and resist extra steps in the worm composting process. My normally method of food waste collection is to place an uncovered 5-gallon bucket outside the back door and simply toss in whatever I plan to send to the bin.

This doesn’t come with downsides though!

Heavy rains can partially fill my bucket with water. Squirrels are plenty interested in what I put in there. The food waste can start rotting, And fruit flies and other insects can appear.

But so long as I add dry bedding to soak up the moisture and wring it out before adding it to the bin, all of the above problems go away within a couple days of adding the waste to my Urban Worm Bag.

As a general matter, I don’t tell people they should freeze waste, and I totally get the anti-zero waste aspects of it. But the reasons to do it can be pretty compelling! If you can preserve food waste for when you need it AND speed up its eventual decomposition, then freezing isn’t a bad way to go.

Tell me your story. Are you freezing or not?

31 thoughts on “Vermicomposting 101: Freezing Food Waste for the Worm Bin. Is It Necessary?

  1. Steve, I guess I’m not too concerned about the negative footprint of freezing food waste. Mostly because the freezer contains “human foods” it is protecting from decomposition. Therefore adding a pound or two of “worm food” doesn’t impact the operation of the freezer to a great extent. However I have found the freezing of raw food waste to be beneficial in the final analysis. Worms DO consume the consommé of frozen waste much quicker and appear to be much happier because of it.

    1. The fuller the freezer the less energy it will consume. True: the introduction of non-frozen worm food will require energy to freeze initially (increased energy cost), but thereafter it will increase the efficiency of the freezer (lower energy cost). It is unclear that keeping a good amount of frozen food on hand for worms in a freezer already used for human food actually increases the carbon footprint.

  2. Definitely freezing the food. We produce more than my 2 bins can handle. Plus during the cooler months, here in Florida, the worms slow way down. I hardly feed anything during those months but I hate to throw it in the garbage. For me, it’s not just about having black gold for my garden. It’s also about keeping waste out of the local landfill. But I have gotten more selective of what I keep and freeze, just because it does pile up fast. And freezing it, does make it break down, so it’s more accessible to the worms, quicker. I wish I had a small freezer, just to store worm food.

  3. My story. If you’re referring to the (approx) 50 kilos of fruit/veg waste in the deep freeze, then Yes, I freeze and I’m not ashamed of it. If anything, blame it on the worms. They’ve just got to learn to eat faster. Anyone who complains about ‘waste of energy’ and ‘carbon footprint’ is more than welcome to give up their gas-guzzling vehicles and a host of other electrical items that they use on a daily basis and don’t even think about it.

  4. I don’t have room in my freezer for this. Any extra (usually only during winter when worms aren’t eating much) is put in my regular compost bins.

  5. I’m curious about how quickly microbes recolonize the food once it has been thawed. Freezing probably kills most of the bacteria originally on the food, so pre-frozen food is probably mostly sterile when it goes into the bin. This would mean that the microbes in the bin must colonize the sterile food in order for it to decay. If that colonization process took a long time, it could potentially take longer for frozen food to break down than unfrozen food, even though the cells had been burst. All the anecdotal evidence that I’ve heard says that frozen food decays faster, but I do wonder if anyone has run any controlled tests.

    Secondly, I wonder how freezing the food affects the bacterial diversity in the bin. If most of the food introduced to the bin has been frozen, will the bin end up having fewer species of bacteria and fungus living in it? Is having more species better (I’m guessing probably?)? There’s also the chance that freezing is not a problem for food going into an established bin, but could slow down new bins by keeping them from developing diverse bacterial colonies.

    1. Unlike certain larvae and bugs, most bacteria slow down drastically when frozen but are not killed by the freezing. When thawed, they “wake up” to an environment of broken-down cells in the waste that is even more hospitable to reproduction. I think this is one of the reasons you should never re-freeze foods that have thawed once already.

  6. I do both but usually freeze my food waste. I have dogs so keeping it outside until ready to use won’t work and my bin is inside my home. It seems I’d be spending the same amount of energy to maintain the food waste outside and prepare it for my inside bin as I do freezing?

    If I collect too much in the freezer, I take it to my community garden compost bin.

  7. I freeze all my food waste for all your reasons plus that in hot weather it acts like a refrigeration for the worms. Put small piles of it in the layers – admit unthaws – voila a cooler bin. Keeping insects at bay is very important for me too.

  8. I love freezing my food scraps. It’s just so convenient, whether it is an apple core, a handful of broccoli stems or a bag full of potato peels! Why, I don’t even have to walk as far as to the back door to throw it into a bucket. And then, come time to feed, I get out the amount I want of nicely prepared worm food. No downside to me!!! (:

  9. I freeze when I have room in the freezer. The worms process it much faster, which benefits them, and it practically eliminates the fruit fly/rotting fruit problem, which benefits me. As for the energy issue, I do a lot of things to save electricity (thermostat set to 62 in winter/78 in summer, never use the TV, hang clothes to dry instead of using the dryer, etc.), so I’m not concerned about using a tiny bit of power to freeze food waste once or twice a month.

  10. Already getting into the 100 degrees in Sacramento! Just started vermicomposting in the garage 5 months ago and doing well, I think.

    Is it Ok to feed all frozen food to try to keep cool? Not sure I want the tower in the house.

    1. Hi Deb,
      If that’s what needs to happen to keep it cool enough in your bin, then sure, freezing is fine. Try to take the temps in the bin to see what they’re actually reading. They may be a bit cooler than the temperatures in the garage itself.

  11. I just started my bin yesterday and I’m thinking of freezing because I live in a Caribbean Island and is mango season. I have bunch a mangos and only a 400 worms bin. Is it right to keep mangos frozen? Do worms like them and are mangos good for composting?

    1. Hi Richard,
      That should be just fine, but with only 400 worms, you won’t be able to process too many of these mangos until your bin grows a out to a larger population!

  12. What is the best way to thaw the frozen scraps without attracting insects and whilst still eliminating the excess water? I have an indoor tray system bin, so adding bedding every time I feed in not an option unfortunately. Ps, my 2 home made bins out side, started a year ago, has a thriving population, one with reds and the other night crawlers, and some of the worms are 6+ inches long! This is such a blast for me and my 5 year old Son and we have thoroughly enjoyed learning from all you fellow Vermi friends! God Bless All!

  13. Thanks for this. I’ve been mystified by people dumping in frozen food. Since I lost worms to freezing weather, I’d never subject them to that! Seems to work for people , though. I freeze for one reason: to thaw it and get the moisture out. I’m currently using a tray system (and have asked for an UWB for the next gifting occasion!) and it’s a battle to keep the moisture level down. I thaw, drain, and then wring the scraps out to pretty much the level of moisture that the bedding has. I used to wrap them in newspaper when there was still a newspaper…but this at least helps.

    1. Hi Melody – I also freeze but the neatest way i found to get rid of extra moisture is to use one of those Spinners they used to take moisture off lettuce. Thaw and spin and put drained liquid in outdoor compost.
      Picked one up at second hand store really cheap. You dont want to spin it too dry though.

  14. I have a thought about this process. What if the food is frozen to get rid of fruit flies, then added to a container with compost and bedding. This could get the microbes working on it before adding to UWB. Any thoughts on this?

  15. I am looking to start composting how much fruit flies are we talking? I want to keep this inside as it gets quite warm in the summer. I already have fruit flies swarming my collection bucket that I keep on the counter is a composter just as bad or worse? Will freezing help keep them down?

    1. Freezing the food waste will help greatly and you bring up a good point about fruit flies in a worm bin. They (or their larvae) are often present on the food waste before it ever gets into the worm bin.

  16. I freeze potato peelings, otherwise they grow from each and every “eye” on them, whether put in the worm bin or my cold compost heap. That freezing kills the potato. I then thaw, collecting the leachate which is simply put out onto garden ground, and the peelings are fed to the worms. All other household scraps (no meat or dairy is ever wasted) are composted. I have plenty of feed without using household scraps, but the walking order of freezer and worm bins in an almost dedicated shed for the worms (8 x 3 high DIY boxes) make it convenient to feed them whilst preventing any problems from volunteer potatoes.

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