What is bokashi? Kitchen waste fermentation explained

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A sealed bucket under the sink, a few handfuls of bran boosted with EM-1 sprinkled over the peelings, and meal leftovers that ferment instead of rotting: that is bokashi. The method intrigues people because it accepts waste that garden compost heaps and worms turn their noses up at, and because it fits in a kitchen. Understanding what goes on inside the bucket helps you avoid most beginners' mistakes.

Bokashi: a Japanese word for matter "softened" by fermentation

The word bokashi is often translated as "fermented organic matter". It refers to the method, to the fermented product you end up with and, by extension, to the bran used to start the fermentation.

In practice, kitchen bokashi relies on three things: an airtight bucket fitted with a grid and a tap to drain off the liquid, your food waste, pressed down layer by layer, and an activator, in other words cereal bran fermented with micro-organisms. We cover the latter in detail in our guide to bokashi bran.

Did you know?

In Japanese, the verb bokasu means "to blur" or "to soften", as you would blur a colour gradient. Japanese gardeners use the word bokashi for a fertiliser made of rice bran and oilseed cake mixed with soil and then fermented: this "softens" the strength of these materials, making them gentler on roots.

Fermenting is not composting: the gherkin principle

Conventional compost is decomposition in the presence of air. Bacteria, fungi and small creatures consume the material while breathing oxygen; the heap warms up, loses water and carbon dioxide, and gradually turns into humus.

Bokashi follows an entirely different logic: that of preserving. In the sealed, tightly packed bucket, there is hardly any air left. The lactic acid bacteria introduced by the bran convert some of the sugars in the waste into lactic acid. The environment becomes acidic, and this acidity holds back the microbes responsible for putrefaction. It is exactly what happens when you make gherkins, sauerkraut or the silage farmers feed their livestock in winter.

The result: your waste is not digested but preserved. It keeps more or less the same appearance, takes on a sour smell of vinegar or pickles, and is sometimes covered with a thin white film, which is a good sign.

Another difference from compost: a bokashi bucket barely warms up at all. Lactic fermentation releases very little energy compared with decomposition in air, and most of the material, and therefore the nutrients, stays in the bucket.

Who is at work in the bucket?

Bokashi activators are generally made with effective micro-organisms, or EM. According to manufacturers, these blends mainly combine lactic acid bacteria, yeasts and photosynthetic bacteria. You will find their history and composition in our guide What are effective micro-organisms.

In the bucket itself, lactic acid bacteria call the shots. The few published analyses of household buckets show that they make up the vast majority of the microbial population, both in the starting bran and in the bucket at full fermentation. Yeasts and other groups are far less prominent, and their exact role in bokashi is still poorly understood.

Their work shows up in the pH, that is, the level of acidity. The liquid drained from the tap usually measures between about 3.5 and 5, an acidity comparable to orange juice or yoghurt. That is why the contents of the bucket are never placed directly at the foot of plants, and why the liquid is always heavily diluted.

The two stages of bokashi

Stage 1: fermentation in the bucket

You fill the bucket day by day, sprinkling each layer with bran and pressing it down firmly. Once the bucket is full, you leave it closed for at least two weeks in a room at a moderate temperature, draining off the liquid from time to time. As this phase ties up the bucket, most users have two: one being filled while the other ferments. Detailed instructions can be found in our guide Starting your first bokashi bucket. In the diagram: fermentation in the bucket (1), then transformation in the soil (2).

Stage 2: transformation in the soil

What comes out of the bucket is an acidic pre-compost, not compost. It needs to go into the soil: bury it 20 to 30 cm deep, well mixed with the soil, away from roots, and wait at least two weeks before planting. You can also mix it into a garden composter or a large container of soil, or feed it in small amounts to worms, with a few extra crushed eggshells to counter its acidity. In the soil, microbial life consumes the lactic acid, the acidity drops and the scraps break down. Depending on the season and soil type, allow roughly two weeks to two months for them to disappear.

Key points

Bokashi happens in two stages: a few weeks of fermentation in a sealed bucket, then transformation in the soil. Without this second stage, there is no compost.

Where does bokashi come from?

Fermenting organic matter before returning it to the soil is an old practice. It is often said to have roots in the Korean and Japanese countryside, where organic matter was fermented to produce a gentler fertiliser. These origins are, however, poorly documented.

The modern version, the kitchen bucket, is linked to Professor Teruo Higa, a horticulture lecturer in Okinawa, Japan. In the early 1980s, he developed effective micro-organisms, a blend of fermentation micro-organisms that he put forward for agriculture. Bran inoculated with EM, sprinkled over kitchen waste, then spread around the world, reaching Europe in particular from the 1990s onwards.

The real benefits and limitations

What bokashi does well

• It accepts almost all food leftovers, raw or cooked, including meat, fish, cheese and citrus fruit. The full list is in our guide What waste to put in a bokashi bin.
• It fits in a kitchen: a 10 to 20 litre bucket, with no contact with the soil.
• It preserves the material: since the bucket does not heat up and stays closed, relatively little material is lost as gas during fermentation.
• It takes little effort: chop, sprinkle, press down, close, drain the liquid. Nothing needs turning, and above all, you never stir.
• The smell stays faint with the lid closed. When you open it, it smells sour, like gherkins, sometimes a little like beer or cider.

What you should know before buying

• It is not finished compost: after two weeks, you have a pre-compost that still needs to go through the soil, a composter or worms.
• You need an outlet: a garden, a container of soil, a composter, or a friend or relative who wants it.
• It uses activator continuously: you need to buy more or make your own.
• It does not take garden waste: grass clippings, dead leaves and branches remain a job for the composter.
• It requires a little discipline: a bucket that is poorly sealed, too wet or not sprinkled enough can rot instead of fermenting.

Emy's tip

Keep a small lidded caddy on the worktop during the day, and empty it into the bokashi bucket just once, in the evening. The less you open the bucket, the less air gets in, and the better the fermentation.

Is bokashi right for you?

Bokashi will suit you particularly well if:

• you have a garden, a vegetable plot or large containers, and you want to return all your kitchen leftovers to them, including those a composter struggles to digest;
• you live in a flat but have a regular outlet: a community garden, a friend's or relative's plot, a large container on a balcony, a shared compost point;
• you already have a wormery and are looking for a solution for meat, fish and citrus fruit.

It will suit you less if you have nowhere to return the pre-compost to the soil. In that case, a wormery, which produces a ready-to-use soil improver, will often be simpler: our guide explains how a wormery works. To compare the methods point by point, read our guide Bokashi, compost or vermicompost.

To get started, all you need is an airtight bucket with a tap, such as the Composteur à Bokashi Confort or the Skaza Organko 2 Bokashi Composter, and our Bokashi EM Compost Activator, made on the farm. Finally, our guide Bokashi and EM: what the science says reviews the studies.

In a nutshell

Bokashi is the lactic fermentation of kitchen waste, carried out in an airtight bucket using bran loaded with micro-organisms. In about two weeks, the scraps become acidic and are preserved rather than rotting, without heating up and with a faint, sour smell. This pre-compost then needs to be returned to the soil, a composter or worms, which complete its transformation within a few weeks. It accepts almost all food leftovers in very little space, provided you have an outlet and a supply of activator.

Related products

Best Seller

Bokashi EM compost activator | 1 kg bag

Individually or in sets of 2 or 3 bags

£5.99 €7.18

Urbalive Bokashi Composter

Capacity 10.6 litres, available singly or in a set of 2

£54.91 €65.83

Bokashi Composter Skaza Organko 2

Capacity 9.6 litres, individually or in a set of 2

£56.30 €67.49

Skaza Essential Bokashi Composter

Capacity 15.3 litres, set of 2 buckets

£53.53 €64.17

Other topics in the guide

Vermicomposting30 sheets →Composting25 sheets →EM micro-organisms26 sheets →