Most home composting systems will break down garden waste and uncooked kitchen waste such as vegetable and fruit peelings, but can't be used to dispose of cooked food, meat, fish or dairy products.
These need special treatment as they tend to putrify, producing rotting smells and attracting flies and vermin, so often they just go in the bin for landfill.
The bokashi system
Bokashi is a method of composting developed in Japan in the 1980s, based on techniques used for centuries in Asia.
It is a very simple two-stage process which uses naturally occurring beneficial microorganisms to ferment kitchen waste before turning it into traditional compost.
Bokashi bran containing a mix of microorganisms and molasses is sprinkled throughout the waste, which is then sealed up in airtight bins for about two to three weeks. The resulting 'pickled' waste breaks down in just a few weeks when mixed with soil or compost.
Bokashi bins are generally quite small with tight-fitting lids, and usually have a tap near the base for drawing off the bokashi 'tea' produced during fermentation. They are intended to be kept in or near the kitchen as the fermentation needs warmth. The process is very clean and doesn't smell or attract flies.
Filling the bin
Almost all kitchen waste can be processed, including cooked and uncooked meat, fish, small bones, pastry, bread, dairy products, eggs, plate scrapings, fruit and vegetables, cooked left-overs, tea leaves and coffee grinds.
Only fresh food waste should be added to the bokashi bin, never anything mouldy or rotten, and no liquids, such as milk or fruit juice, or very wet foods, such as leftover soup. Large scraps of food and bread should be cut up into small pieces. Bread can be a problem if too much goes in at once - half a stale loaf added in a single layer can upset the balance of bacteria during fermentation.
Tea bags must be well squeezed out, or can be added to the garden waste instead (check that the bag is compostable - some contain plastic).
Bokashi bins work best if they are not opened too often, so collect the scraps up in a caddy and add them to the bin all in one go, rather than constantly opening and closing the lid.
Begin by sprinkling a little bokashi bran on the strainer in the base of the bin. Add a layer of food waste, then sprinkle more bokashi bran over the top of the waste. Use approximately one tablespoon of bran to every 3-4 cm depth of food. If in doubt, add more. It's always better to add too much rather than too little to ensure complete fermentation and good smelling compost, and use extra for high protein foods such as meat, fish, cheese and eggs.
The less air in the compost the better, so compact the waste by pressing it down lightly with a flat plate or a potato masher. Always replace the lid tightly to prevent smells developing and stop flies from getting in.
Continue this process until the bin is full, draining off any liquid that has accumulated at the bottom every couple of days.
When full, ensure the container is tightly closed and air-tight and leave it in a warm place away from direct sunlight to ferment for at least 2 to 3 weeks. It's best to have two bokashi bins, so when one is full and fermenting, the other is being filled up.
Drain off any juice from the bin every couple of days during the fermentation period.
IMPORTANT This is an anaerobic process so don't open the container at all for at least 2 weeks to allow the fermentation to complete.
When ready, the fermented waste should have a quite pleasant yeasty, sweet and sour smell, like pickles or cider vinegar.
Bokashi treated waste is not composted in the bin. The food will still be recognisable - bread will still look like bread - although the process does change the structure of the food, giving it a slightly spongy texture.
Sometimes a white cotton-like fungal growth appears on the surface. This is not a problem, and indicates that good fermentation has taken place.
If the bin smells bad or there is green mould, something has gone wrong! See our post on bokashi troubleshooting.
Composting the fermented waste
The fermented waste now has to go through another process to break it down into useable compost.
This can be in the ground, in a compost bin, or mixed with potting compost.
The easiest method is to simply add the contents of the bokashi bin to a compost bin. Spread the fermented waste out and mix with a little compost to speed decomposition. Cover over with more compost and/or a layer of garden waste.
Another simple method is the 'Soil Factory'. This can be used to revive old used potting compost or to enrich new commercial or home-produced compost or soil. Tip half a large bag or about 20 litres of compost or soil into a large container. Mix in the contents of the bokashi bin, then add another 20 litres of compost or soil on top. The mix should be moist but not soggy. Cover and leave for 4 to 6 weeks before using. If you are not ready to use the mix you can add more layers on top.
You can also use the bokashi mix directly in large planters or raised beds - fill the container about one-third full with potting mix, add about the same amount of fermented bokashi and mix in, then fill up the rest of the container with more potting mix. Leave it to settle for a couple of weeks before planting up.
Add to a worm composting bin. We find it best to just add a little of every batch to the worm bin. The waste is very acidic and it should be added just a little at a time. The worms do like it, but they avoid it for a few days until the acidity levels drop. It can get quite smelly unless covered with fresh waste.
Digging the fermented waste directly into the garden. Dig a hole or trench approximately 20-25 cm deep, add the fermented waste and mix in some soil, then cover with the remaining soil. The waste will break down more quickly if you can spread it in a thin layer an inch or two deep, rather than dump the whole binful in a heap, as it needs to interact with the soil bacteria and earthworms.
Bokashi mixtures are acidic when first dug in. Ensure plant roots do not come directly into contact with the fresh waste as it may burn the roots, particularly in young plants. The mix will neutralise after 7-10 days, so wait a couple of weeks before adding any plants.
The waste will break down very quickly in the ground - usually this takes about 3 to 4 weeks.
If you have an inquisitive dog which likes to dig it's best to cover the area where the waste is buried for a week or two, or bury it deeper.
The video below by Sara Bäckmo is a really good demonstration of how quickly the bokashi waste disappears once it's dug into the ground.
Generally a liquid is produced during fermentation, although don't worry if there is none. The amount and colour depend on the type of foods you have put into the bin - fruit and vegetables will produce more than other foods. Any liquid will drain to the bottom and should be drawn off every couple of days.
This bokashi 'tea' doesn't keep well, and should always be used within 24 hours of draining from the bin or it gets really smelly. For that reason, never add to a water butt!
Bokashi tea contains the fermentation products from the food waste and makes an excellent plant fertiliser. To fertilise garden or container plants use about 1 teaspoon (5ml) to 5 litres of water, or for established trees and shrubs use 2 teaspoons (10ml) to 5 litres of water. Always apply directly onto the soil, never onto foliage.
The undiluted liquid can be poured down kitchen and bathroom drains or toilets or into septic tank systems, where the micro-organisms will help to control odours and prevent algae build-up.
There is an initial cost in purchasing the fermenting bins, (see *here) plus the ongoing cost of bokashi bran. Each fermentation cycle uses very roughly 200 grams (just under half a pound) of bokashi bran. Prices vary, but bokashi bran costs on average about £7 to £10 per kilo in the UK (See *here )
You can reduce this cost by buying larger packs - bokashi bran has a shelf life of about one year. Or you can make your own bokashi bran - see our post on DIY bokashi bran here.
You do need somewhere to empty the bins to complete the composting process, either your own garden, or maybe in a friend's garden, a community composting scheme, or at the local allotments.
Converts all kitchen waste into useable compost, including food scraps such meat, fish and cooked wastes which normally aren’t composted, reducing the amount of waste sent for landfill or incineration.
The container takes up very little space and the process is odour free so it can be kept in the kitchen.
Bokashi composting is very easy, and can be done on any scale.
Organic matter is broken down into compost within a couple of months.
The final compost fertilises and improves the soil and adds beneficial microbes.
The liquid produced can be used as fertiliser, or to keep drains clear of algae.
Greenhouse gas emissions are low in both the fermenting process, and in the rapid composting process at low temperatures.
(Note. Bokashi bran can also be added to chicken food to reduce the acidity and smell of their manure. Feed daily at a rate of 5% of the weight of their feed and sprinkle on the dropping tray under the perching bars.)
The video below is really informative and covers all aspects of the bokashi system, including making your own bran. It's by Daphne Lambert of the Greencuisine Trust, a food education charity exploring our relationship with food and encouraging ways of growing and eating that nourish people without harming our environment.
Book *Bokashi Composting: Scraps to Soil in Weeks by Adam Footer at Amazon UK
See also our other posts::