Bokashi Composting in Singapore: How to Ferment Food Scraps Indoors

Most guides treat bokashi as a shortcut to compost. A bin you fill, a tap you drain, and two weeks later you have soil. That is not what happens. Bokashi is an anaerobic fermentation process that uses effective microorganisms to pickle food waste, not break it down. The material that comes out of a bokashi bin is a fermented pre-compost, not mature compost. It smells like brine, not earth. It still looks like food. Bury it directly in soil and it finishes decomposing in two to four weeks. If you do not have soil, and most HDB flat residents in Singapore do not, you need a separate step called a soil factory to convert fermented waste into potting mix. That soil-factory method, a container of potting mix on a balcony or common corridor, is the standard solution for indoor bokashi composting in Singapore. Without it, the bin fills, you run out of storage, and the system stops working.

Aerobic composting, the kind in a tumbler or a pile, relies on oxygen and heat. Microbes break down organic matter and the pile gets hot enough to kill seeds and pathogens. Bokashi works without oxygen. The fermented bran contains lactobacillus and other effective microorganisms. Layer food waste with bran inside a sealed bokashi bin and fermentation starts. The bin never heats up. The process stays at ambient temperature. After roughly two weeks the waste has been pickled, not rotted. It is safe to handle, does not attract flies in the sealed container, and can be stored for weeks before you deal with it. That storage window is the key advantage in a small flat: accumulate fermented waste until you have enough to set up a soil factory batch. The trade-off is that the bin produces leachate, often called bokashi tea. Drain it every few days and dilute it about 1:100 before you use it as a liquid fertiliser or pour it down a drain.

What to Do With the Leachate

The bokashi bin has a spigot at the bottom. Drain the liquid every two to three days. Straight leachate is too acidic for plants. Dilute it at about 1:100 with water and water your garden or potted plants. Or pour the undiluted leachate down the kitchen sink. It is acidic enough to act as a drain cleaner and the microbes are harmless to a sewer system. If the leachate smells putrid rather than sour, the fermentation has gone wrong. The bin was not sealed properly or the bran was old. Open the bin, remove any mouldy patches, add extra bran, and reseal.

Unlike aerobic composting, a bokashi bin accepts cooked food, meat, dairy, small bones, and oily scraps. Exclude large bones and liquids that would flood the bin. The anaerobic fermentation handles all kitchen food waste types common in Singapore. Layer every addition with a handful of bran, press down firmly to exclude air, and reseal the lid immediately. Open the bin only for the few seconds it takes to add waste. Fruit flies enter through a loose lid seal, so check the rubber gasket every time you close it. If flies appear, clean the lid and gasket with vinegar and add a fresh layer of bran on top of the waste.

Bokashi bran is available from several online sellers on Lazada and Shopee. Search 'bokashi bran Singapore' and you will find 1 kg bags for about $8 to $15. Some sellers offer wheat bran inoculated with effective microorganisms; others sell a pre-mixed product. The bran has a shelf life, usually six months to a year if stored dry and cool. Do not buy more than you will use in a few months. A 1 kg bag lasts a two-person household roughly two to three months, depending on how much food waste you generate. You can also find bokashi bran at a few local gardening shops and community garden supply points, but the online route is more reliable. If you cannot find bran in stock, the alternative is to buy effective microorganisms as a liquid culture and inoculate your own wheat bran. That adds a step most home users skip. The ongoing cost for a household running bokashi full-time is roughly $4 to $8 per month in bran.

How To Set Up A Soil Factory

Buy a 20- to 30-litre bucket with a tight-fitting lid. Fill it halfway with standard potting mix from any garden centre. When your bokashi bin is full, empty the fermented waste into the bucket, stir it into the potting mix, and seal the lid. Leave it for two to four weeks. Open it once after a week to stir again, then reseal. After four weeks the contents should look and smell like earth, not pickles. Use the finished compost as a soil amendment. Mix it into your potted plants or top-dress them. Do not use it straight as potting mix without diluting it with fresh potting mix. The compost is nutrient-rich and can burn plant roots in high concentration.

What Happens If You Skip This Step

Without a soil factory, fermented bokashi waste has nowhere to go. You cannot leave it in the bin indefinitely. You cannot throw it in the common rubbish chute without losing the point of the system. A second bucket of potting mix solves the problem in a flat with no garden. It also produces mature compost you can give to a neighbour or donate to a community garden. The soil factory is not an optional extra. It is the step that makes bokashi viable in an HDB flat.

How Much Food Waste One Household Diverts

Singapore generated 755,000 tonnes of food waste in 2023, according to NEA figures. Roughly 30% came from households. A two-person household in an HDB flat generates about 2 to 3 kg of food waste per week. Running a bokashi bin full-time diverts a significant volume of food waste per person per year from incineration. That food waste would otherwise be incinerated, producing incineration bottom ash that is barged to Semakau Landfill. Every kilogram of food waste kept out of the incineration stream reduces the ash-to-waste ratio and extends the lifespan of Semakau, which NEA projects to reach capacity around 2035 at current disposal rates. The food waste that goes into a bokashi bin never reaches an incineration plant. It becomes mature compost that returns nutrients to soil instead.

Where to Put the Bin in a Small Flat

Keep the bokashi bin in the kitchen, under the sink or beside the rubbish bin. It needs to be close to where you prepare food. A sealed bokashi bin does not smell during fermentation, so it does not need a balcony or outdoor space. The soil factory bucket needs a spot on a balcony, a common corridor shelf, or a stairwell landing. It sits sealed for weeks at a time and requires no daily attention. Check that your town council permits items in common corridors before placing one there.