Bokashi - Composting Cooked Food Waste for Your Garden

One of the highest priorities when establishing a garden is to create a good composting system. Of course, it’s possible to feed your plants with commercially produced compost and fertilisers but home composting is so easy, cheap and effective that it makes sense to recycle as much as possible back into the soil. However, most home composting systems have a limitation: you can’t put cooked food waste, dairy products, meat and fish into them as they will putrify, producing bad odours and attracting rats and flies. It all adds to the huge quantities of waste food which are sent to landfill by households, millions of tonnes per year. This is where bokashi comes in – it’s an easy way to compost your cooked food waste so it can end up nourishing your garden rather than in landfill.

How Does it Work?

Bokashi is a composting system which originated in Japan and is ideal for use in the home. Unlike traditional composting it relies on adding Effective Microorganisms (EM) which are a mixture of bacteria and yeasts that break down the food using a fermentation process. Also significant is that the bokashi process is anerobic as practically all air is excluded, whereas normal composting needs plenty of air mixed in.

In practice this involves having a separate bokashi bin in the kitchen to which food waste is added. To keep the process anerobic it’s best to store up the cooked food waste and add it to the main bin once a week. Bokashi bran is then spread thinly over each 3-4cm (1-1.5in) layer of food to introduce the EM, the mixture is pressed down and then the bin lid is tightly sealed. If the food being added is in large chunks then it needs to be chopped up into pieces so that the EM can get to work on it. This process is repeated until the bin is full, after which it is ready. Depending on the types of foods which have been added to the bin it is quite common to get a coloured liquid at the bottom which needs to be drained off every 2-3 days. This ‘bokashi tea’ also contains the EM and has a variety of uses including feeding soil and household cleaning.

Although described as a composting method bokashi is really more like a pre-composting process. It starts to break down the food quickly but at the end the mixture still looks vaguely like the food that was put in and is too acidic to use directly on plants. Instead, it is best to either add it to a regular composting bin or to dig a trench about 30cm (1ft) deep and bury it about 2-4 weeks before growing any plants in the area so that normal composting can take place.

Bokashi in Practice

My family and I are vegan so we don’t have dairy, meat and fish to compost. However, with a toddler in the house we do still have quite a lot of cooked food waste to dispose of so I was keen to try out the bokashi system. I purchased a special bokashi bin which includes a small tap at the bottom to make it easy to drain off the bokashi tea and set up a second small bin to collect the cooked food waste in before adding it to the bokashi one.

Adding the food and bran to the bokashi bin was easy and, just as advertised, the EM meant that there were no unpleasant odours, just a slightly sour fermented smell when opened. The smaller bin we were using to collect food before adding it did need cleaning out regularly though. Pretty much anything can be added to the bokashi bin (apart from anything rotting or high in liquid content like soup) but during hot weather the collection bin can start to smell if the ‘only add bokashi material once a week’ rule is adhered to.

I soon found that it would be better to have ordered two bokashi bins, since once you have filled one you need to leave it sealed indoors for two weeks (slightly longer in cold weather) before it can be emptied. Having a second bin means you can be filling that while the first one is completing the fermentation process.

The bokashi tea that I drained off was a dark red colour and can be diluted 1:100 to water into the ground around plants, not directly onto the plants themselves, which I did regularly. The tea needs to be used within 24 hours of draining. I’m not sure how much benefit this made to my soil and it seems that the jury is still out on this one although the manufacturers make bold claims. However, the liquid was particularly good when used in drains. During hot summers we have a problem with a couple of smelly drains and I don’t like adding bleaches which are so bad for the environment. Adding the bokashi tea (undiluted) made a big difference – the EM cleared up the nasty smell within a few days.

Benefits and Drawbacks

Once the bokashi process had completed I added it to my regular compost bin. From a second batch I dug the resulting fermented mush into a trench a few weeks before planting peas and beans. It’s difficult to say if the bokashi had much effect – the beans seemed to grow slightly higher where I had added the bokashi material but that could have been natural variation or the influence of other plants. However, having extra material for the compost bin was welcome since I never manage to produce as much new compost as I would like for my garden.

The biggest drawback of the bokashi system is without a doubt the expense of having to buy the bokashi bran. It costs about £5 ($8) per 1kg bag, which I found lasted us two bin-fulls, although it’s slightly cheaper if bought in bulk. I estimate the total cost for an average family could be up to £50 ($80) per year which is why it’s advisable to run a standard composting system for uncooked fruit and vegetable waste too.

There are alternatives – you can make your own bokashi bran by just buying the EM liquid and mixing it with molasses and wheat or rice bran carefully following the instructions. Various blogs claim to have found ways of producing EM without needing to buy it using everything from fermented rice and milk to various special teas. I have to say I’m a bit sceptical about home-made versions producing the right types of bacteria and yeasts that make bokashi work so well.

The big question is whether the expense of the bran justifies the extra compost that is produced. Of course from an environmental standpoint there is no question that it is much better to be recycling more food waste into the garden rather than sending it to landfill. However, for bokashi to catch on, it needs to give economic benefit as well and I think it just about does. The quantities produced are not huge but they are rich in nutrients for plants and with the added benefit of the bokashi tea with all its uses I think this will be one extra composting technique that I’m prepared to invest in.