A woman scrapes veg scraps into a compost bin.

How To Stop Indoor Compost Bins From Smelling

You can minimise or eliminate the smell of indoor compost bins, if you take the right steps. Fortunately, it’s not hard to produce indoor compost without stinking your kitchen out. In this article we’ll cover everything you need to stop your compost from becoming smelly.

I’ll be honest, I’m not allowed to compost in the house. My wife and I have very different views on what’s acceptable, and while I can do what I want in the garden and greenhouse, I am banned from composting in the kitchen – other than a small compost caddy which I am expected to empty daily.

Most of the time that means it doesn’t smell, especially now I use a bin with a charcoal filter. The only time it does smell is when food clings to the inside. My chicken food bin, which is where more cooked waste goes, is usually a more likely culprit. 

Fortunately, I have a garden to compost in, so that’s not really a big deal. But while everyone has waste, not everyone has the space to compost outside.

It is perfectly possible to compost inside without causing a nasty smell. In fact, in my recent experiment with micro-composting the only smell I got was a faint citrus smell, only detectable when I opened the top of the bin. That’s not the only option, and we’ll cover them all in this article.

Contents

Collecting Compost for Outside

Regular emptying

We’ve collected compost for years now and we’ve rarely had a smell. Not from the compost bin, that is – we’re more likely to get a smell from the chicken food collecting bin! 

To be fair, having chickens is one reason my bin gets emptied daily. I have to attend to the chickens every day, whether it’s sunny, raining or, as recently, in the middle of a howling blizzard. While I am out there, it’s only a extra few seconds to dump the compost waste in my HotBin. 

Regular cleaning

I must admit I am better at regular emptying than regular cleaning! But honestly, when I say regular i don’t mean every day. The real thing to watch out for is when food starts clinging to the side. When it does, a quick rinse off usually does the job, with a more thorough clean a couple times a week. 

Odourless Compost Caddy

I’ve recently been experimenting with an odourless compost caddy. This bin uses a charcoal filter that absorbs and smells.

Although the one I’m using is cheap, and frankly a bit flimsy, I’ve detected no smells so far. 

Rather more stylish is the Joseph Joseph Intelligent Waste bin. It combines a general trash bin with a removable compost bin.

Both the main bin and the compost bin have charcoal filters to absorb smells, while the ventilated compost bin allows air to circulate to reduce moisture.

Also see: Best Kitchen Bins (USA)

Composting inside

Composting inside is a different matter, of course. Instead of simply collecting compost for a few days you could, depending on the system, be keeping the compost in a bin for weeks on end. 

Let’s have a look at the different options. 

Bokashi bins

Bokashi bins do not actually produce compost. Instead, they produce a pre-compost which needs to be dug into the ground or the compost heap. They are a popular solution for indoor composting, though, and so worth including here. 

Bokashi bins are not odourless. They produce a fermented/pickling smell as opposed to a rotting food smell. Most people find this offensive, some people like it and some people loathe it. See our guide to Bokashi bins for more information.

Worm bins

If you’re brave enough to share your home with dozens of ‘red wriggler’ worms, you might consider having a worm compost bin. Compost worms, usually the ‘red wriggler’, not only help break down the material, they can also remove diseases like E-Coli!

As long as your worm bin is set up correctly it should not smell. 

Cardboard box composting

Cardboard box composting is little known in the West, but is popular in Japan. The composting takes place in a well-ventilated corrugated cardboard box in which you place coco peat and rice husk charcoal. (Hardwood ash can also be used.) You can then add your kitchen scraps. 

The ash absorbs any liquid. As long as the box is well ventilated, aerobic composting will take place, ensuring there are no foul smells. You do need to cover the top with an insect-proof screen (an old t-shirt will do).

You can find cardboard box instructions here (use Google Translate to view them in English.)

What causes smells

So far we have looked at collecting compost and alternative composting systems. But what if you want to do more traditional composting inside? 

It’s certainly possible, as I found when I did my micro-composing experiment. But how can we minimise smells?

Ideally, our waste is turned into compost by aerobic (i.e. with air) organisms, which can turn waste into compost with limited smell. But if conditions are not right, anaerobic organisms take over, creating unpleasant smells in the process.

Not enough ‘browns”

Every compost heap should have a mixture of greens and browns.

(Greens here refer to things which are high in nitrogen, such as kitchen peelings, vegetable waste and most foods. Brown refer to things which are high in carbon, such as old newspaper. For more on the science see Carbon:Nitrogen ratio.)

Don’t worry too much about the exact ratio. The things you put in will all have different levels of nitrogen and carbon and unless you want to have a calculator out every time you put something in your compost bin it’s not worth worrying about. Just aim for a roughly even mix, or ideally slightly more greens than brown. If it does get smelly, try adding some more browns.

When you have the right number of greens and browns, if you have the time you are better mixing them together rather than adding them in layers.

Not enough air

To compost properly, the microbes in your compost heap need air. Without at least 5% air, the aerobic (‘with air’) bacteria can’t function. With my recent experiment, I started off by mixing the compost around my bin on a regular basis to introduce air, and ensured the microbes had enough oxygen to do their job.

Mixing it every couple of days is ideal. And with a small compost bin, mixing is easy and quick.

But if you don’t want to mix, another alternative is to introduce ingredients into the compost that create air pockets – scrunched up cardboard is ideal for this.

Too much water

One cause of a lack of air in the compost bin can be too much water. The water soaks the particles and fills up those air gaps, stopping oxygen from reaching the bacteria in the compost. You then get anaerobic (‘without air’) bacteria, which create an unpleasantly compost smell. (It also takes longer!)

Ideally, you’ll have a tap on your compost which will allow you to drain off the liquid or ‘compost tea’. This is valuable in itself – you can then dilute this down with water and add it to your plants as a fertiliser.

You can also add ingredients that will help soak up the water. Examples included shredded paper (not too much, though, as it can turn into a sludge), a little newspaper or cardboard to soak up the water.

You don’t want it completely dry, though – those aerobic organisms do need some water to get to work. In an ideal world, the consistency of the material will feel like a wrung out sponge.

The wrong type of foods

All foods can be composted, but foods like dairy, meat and fish (both cooked and uncooked) are a little bit ambitious for an indoor system – unless you are using a system designed to handle it, like a Bokashi bin.

Large pieces of waste

The smaller the pieces in a compost bin, the easier it is for the bacteria to work on it. That’s because the surface area of the material is larger. If your bin is too smelly, try putting smaller pieces in.

No soil

Your food waste needs bacteria to break it down. The bacteria usually finds its own way into your own compost, but if you want to speed things up, adding a handful of soil might help.

Lack of Air Space

Materials like wood-chips, leaves and sawdust create air pockets in the compost, ensuring bacteria have sufficient oxygen. 

More importantly for this post, the microbes that live on bulking agent are great for odour control. If you do have an odour problem, adding a layer of sawdust on the top of your compost will quickly remove the smell.

Do ensure that any bulking agent is completely dry before adding it!

Finally…

Whether you have a garden or not, it’s well worth doing your own composting.

Composting rapidly decreases the volume of waste. It also creates a valuable material that you can use for house plants and herbs, and good home composting does without causing damage to the environment. And when you have your finished compost, you have the satisfaction of having turned food waste into ‘black gold’, reducing landfill and saving money at the same time.

Happy composting 🙂