Bokashi composting: ferment food waste indoors

If you've ever wanted to compost but live in a flat, have no garden, or wanted to divert cooked food and the odd bit of meat or fish from landfill, bokashi is worth knowing about.

What bokashi is (and isn't)

Bokashi is a Japanese word meaning "fermented organic matter." The system uses an airtight bin and bokashi bran — wheat bran inoculated with effective microorganisms (lactic acid bacteria, yeasts and phototrophic bacteria) — to ferment food scraps rather than decompose them aerobically.

Think of it like pickling. The scraps don't rot and don't break down in the bin; they are preserved in a slightly acidic state. Because it's sealed and anaerobic, there's no rotting smell, no flies and no need for outdoor space.

What bokashi can handle that a standard compost heap usually can't:

• Cooked food and leftovers
• Small amounts of meat, fish and bones
• Small amounts of dairy
• Bread, pasta, rice and other starchy foods
• Tea bags and coffee grounds
• Fruit and vegetable scraps (the usual compost staples)

What it can't handle: large quantities of liquid (drains the bin and dilutes the bran), very large bones, or mouldy food — add these sparingly or not at all.

What you need to get started

• A bokashi bin with a tap. These are airtight containers, usually plastic, with a tap or spigot at the bottom to drain the liquid that collects. You ideally want two — one filling while the other finishes fermenting.
• Bokashi bran. Sold in garden centres and online. You can also make your own if you want to go further, but buying it is straightforward. A standard bag lasts a few months for a typical household.
• A small container for the kitchen counter to collect scraps between trips to the bin, so you're not opening it constantly.

Running a bokashi cycle

A single bokashi cycle takes about two weeks to fill the bin, then another two weeks for the fermented mass to be ready. Here's how it works step by step:

1. Add a base layer of bran. Sprinkle a thin layer of bokashi bran across the bottom of the empty bin before you start adding food.
2. Add scraps in layers. Add food scraps in layers no deeper than about 3–5 cm at a time. Chop larger pieces to speed things up.
3. Sprinkle bran over each layer. A light, even dusting — enough to lightly coat the surface — is all you need. You don't need a thick layer.
4. Press down firmly. Use a potato masher, a piece of cardboard, or your hand. Pressing out air gaps is important — this is an anaerobic process.
5. Seal the lid immediately. Every time you add scraps, close the lid tightly. Leaving it open allows air in and can cause problems.
6. Drain the liquid every few days. Use the tap to drain the liquid (bokashi "tea") into a container. If liquid sits in the bin it can go wrong.
7. When the bin is full, seal it and leave it. Stop adding food and leave the sealed bin for two weeks. Start filling your second bin in the meantime.
8. After two weeks, the pre-compost is ready to bury or finish. It will look similar to when you put it in, but smell sour and fermented. This is correct.

Using bokashi liquid (bokashi tea)

The liquid that drains from the tap is a by-product of fermentation. It's acidic and concentrated, so it must be diluted before use.

• As a plant liquid feed: dilute 1 part bokashi liquid in 100 parts water (about a teaspoon per litre). Use on soil around plants, not directly on leaves or stems. It provides nutrients and beneficial microbes. Don't use on acid-sensitive plants without care.
• For drains and pipes: pour a small amount of undiluted liquid down the drain or toilet occasionally. The microbes help clean organic matter from pipes and can reduce odours.
• Don't let it sit: use liquid within a day or so of draining. If it smells truly foul (not just sour), discard it — something has gone wrong in the bin.

Finishing the pre-compost

The fermented material leaving the bokashi bin is pre-compost, not finished compost. It's too acidic to add directly around plant roots and hasn't broken down into a soil-like texture yet. It needs a second stage to finish:

• Bury in soil: dig a hole or trench at least 10 cm deep, add the bokashi material, cover with soil and leave for 2–4 weeks. By then, soil microbes will have broken it down into dark, crumbly material that improves soil structure and fertility. Keep it away from plant roots while it's still acidic.
• Add to a compost bin: the acidic bokashi material will accelerate decomposition in a standard outdoor compost heap. Mix it in with brown material and leave it to finish. See our composting at home guide for how to run a heap.
• Add to a wormery: worms love bokashi pre-compost once it's had a day or two to off-gas. Add it in small amounts mixed with bedding material. See our worm composting guide for details.

In an apartment with no garden, you can bury small amounts in large plant pots, share the material with a community garden or allotment neighbour, or add it to a wormery kept on a balcony.

Troubleshooting

• Sour, vinegary smell — normal. This is fermentation working correctly. The smell should be noticeable when you open the lid but should not fill the room.
• Putrid, rotting smell — a problem. Usually means air got in, you didn't press scraps down firmly, or the bin didn't seal properly. Try adding more bran and pressing firmly. If it's very bad, the batch may need to be discarded.
• White fluffy mould — fine. A white mycelium-like coating on the surface is a normal part of fermentation. It's harmless.
• Blue or green mould — a problem. This is unwanted mould, usually from contamination or too much air. Remove affected material and add a generous sprinkle of bran. Prevent it by sealing well and pressing down layers.
• Not enough liquid — normal if dry. Bokashi liquid output depends on the water content of your scraps. If scraps are very dry, you'll get little liquid. That's fine.
• Too much liquid — check scraps. Very wet scraps (lots of soup, fruit juice) can waterlog the bin. Drain frequently and squeeze excess moisture from very wet food before adding.

Bokashi checklist

• Get two bokashi bins and a bag of bokashi bran.
• Add scraps in thin layers, sprinkle bran, press down, seal lid every time.
• Drain the bokashi liquid every few days and use it diluted as plant feed.
• When one bin is full, seal it for two weeks and start filling the second.
• Bury finished pre-compost in soil, add to a compost heap or a wormery.
• White mould is fine; blue or green mould means add more bran and seal better.