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.
One option for composting all kitchen waste at home is to use a normal composting system for uncooked waste alongside a bokashi system for cooked food.
The bokashi system
Bokashi is the Japanese term for “fermented organic matter”. The bokashi system doesn’t compost the food, but instead puts the waste through a fermentation process. The system is based on the use of Effective Microbes (EMs), which are naturally occurring beneficial microorganisms, a mixture of bacteria and fungi. The EMs are mixed with molasses in a natural bran-based medium which is layered with the organic waste in a sealed airtight bucket.
After fermenting for two weeks, although it still looks much the same, the waste is sufficiently broken down to enable it to be mixed into a normal compost or worm bin or buried in the ground, without creating unpleasant smells or attracting flies. It then composts down very quickly.
Bokashi buckets are generally quite small, and are intended to be kept in or near the kitchen. They can be kept outdoors, but in colder conditions the fermentation process slows down.
Collecting the waste
- 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 bucket, 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 need to be cut up into small pieces. Tea bags should be well squeezed out, or can be added to the garden waste instead.
- 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 small handful of bran to every 3-4 cm depth of food. 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 bucket 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 2 weeks or longer. It’s best to have two buckets, so when one is full and fermenting, the other is being filled up.
- It is important to drain off any juice from the bucket every couple of days during the fermentation period. Don’t open the container at all for at least 2 weeks to allow the process to complete. When ready, the fermented waste will have a quite pleasant yeasty, sweet and sour smell, like pickles or cider vinegar.
- Bokashi treated waste is not composted in the bucket. The food will look much the same as it did when it was put in – bread will still look like bread – although the process does change the structure of the food. Sometimes a white cotton-like fungal growth appears on the surface. This is not a problem, and indicates that good fermentation has taken place.
- The bokashi waste has now been pickled and can be safely added to a wormery, a normal compost bin, or dug straight into a hole in the garden and covered over. It will then compost down very quickly.
- Rinse the bucket out with water after each use – don’t use chlorine based cleaner.
Composting the fermented waste
- If you are putting 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. Bokashi mixtures are acidic when first dug in, so 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 neutralize after 7-10 days, so it’s best to wait a couple of weeks before adding any plants.
- This system speeds up the composting process. Bacteria in the soil and waste will break down the organic material very quickly and in about 3 weeks it will have completely decomposed.
- If you are short of space for digging a new hole each time the bucket needs emptying, you can create a disposal point by digging a deep hole, placing gravel or small stones in the bottom, then place a large bottomless plastic bin with a strong lid up to its rim in the ground and fill in the soil around it. Tip in the fermented bokashi mix, stir in a little soil, and replace the lid.
- You can also use the bokashi mix in planters, raised beds or pots – fill the container about one third full with potting mix, add the 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.
- If adding the contents of the bucket to a worm bin or compost bin, spread the fermented waste out and mix with a little compost to speed decomposition. Cover over over with more compost. Worms will avoid the waste for a few days until the acidity has reduced.
- Sometimes a liquid is produced during fermentation, although don’t worry if there is none. The amount and colour of the liquid depends on the type of foods you have put into the bucket – fruit and vegetables will produce more than other foods. Any liquid will drain into the bottom of the bucket and should be drawn off every couple of days. This liquid doesn’t keep well, and should be used within 24 hours of draining from the bucket.
- Bokashi tea makes an excellent plant fertilizer as it contains the nutrients from the food waste and also Effective Micro-organisms (EMs). To fertilise garden or container plants use about 1 teaspoon (5ml) to 2-3 litres of water, or for established trees and shrubs use 2 teaspoons (10ml) to 2-3 litres of water. Always apply onto the soil, never directly onto foliage.
- The undiluted liquid can be poured down kitchen and bathroom drains or toilets or into septic tank systems, where the Effective Micro-organisms (EMs) will help to control odours and prevent algae build-up.
- The bokashi bran can 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.
- Bokashi also can be added to compost heaps or used in composting toilets to breakdown organic matter.
- Converts kitchen waste into useable compost, including food scraps such meat, fish and cooked wastes which normally aren’t composted.
- The container takes up little room and is odour free so can be kept in the kitchen.
- The process is very easy, and can be done on any scale.
- Organic matter can be broken down into compost within a couple of months.
- The compost produces fertiliser, improves the soil condition, and adds beneficial microbes.
- The liquid produced can be used as fertiliser, or to keep drains clear, or added to a septic tank.
- Greenhouse gas emissions are low as the fermenting process is fast, and the waste composts quickly at low temperatures once dug into the soil.
- There is an initial cost in purchasing the fermenting bins, plus the ongoing cost of bokashi bran.
- You do need somewhere to empty the bins to complete the composting process, either your own garden, or maybe in a friend’s garden or at the local allotments.
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