fermented compost - diy style

In the last post, we took a quick look at worm nests, what they are and how they are a critical function of the fermented compost method.  As promised at the foot of that post, this time we're going to look at how to get your own DIY fermented compost system together.

I'll state here that fermented compost is more or less the same as Bokashi Kitchen Composting.  I say more or less, because there are a few minor differences - Bokashi is a proprietary system, developed in Japan, which utilizes a specially designed Bokashi composting bucket, which you can see here:

bokashi kitchen composting caddy

you'll note it has a tapering design, with a lid on top and a tap underneath, from which you collect the juice from the decomposing food waste placed inside.  Inside the Bokashi bucket, you have a filter and it comes with a scoop and a plastic "tamper" for squishing down the food waste:

inside the bokashi kitchen caddy

Bokashi is a Japanese word, meaning "fermented organic matter" and is a system of trench composting method used on "ultra organic" farms, as part of the Kyusei Nature Farming movement - monks who believe in using permaculture based farming practices as a spiritual path to connect with nature's rhythms.  In the original Bokashi system, rice bran is fermented with microbes, is dried out, then mixed with vegetable waste, animal manure and liquid microbe brews and then layered up in the trench, to convert to humus under the soil.  It's similar in many ways to Rudolf Steiner's various preparations, familiar to those who practice Bio-Dynamic Farming.

classic bokashi making

In the 1990's Dr Higa of Ryukyus Univeristy in Okinawa decided to make his own commercial microbe brew and wanted to adapt the Bokashi system for the kitchen - to encourage urban dwellers to engage in this organic system for building healthy, humic soil and so the Bokashi Kitchen Composting system was born. All well and good, but there are a few flaws in the system which can mean the difference between well made and healthy fermented compost and a black, sloppy and potentially pathogenic problem. It seems not all the stages of making fermented compost have translated too well, so here we go back to basics and we look at a DIY method, without the need to buy in to the commercial system.

First, you have to understand that the key to making the best kind of fermented compost is to make sure the system is air-tight, being an anaerobic (without air) process.  Like a stomach, we need to make a chamber which keeps out air, to allow the anaerobic microbes to ferment the food waste, but which allows any liquid to percolate through the microbe-rich bran (we use wheat bran, not rice bran) and collect separately.

For this, we need two empty and air-tight containers, one to fit snugly inside the other, like this:

one fits snug inside the other - an airtight seal

You can see that when they're placed one inside the other, there's a gap at the bottom, between the two containers.  This is where the juice will collect.  In this pic, i'm using two popcorn buckets for demonstration only - you won't fit much food waste in a bucket this size.  If you don't generate much food waste something this size will do you fine, but for a larger family, a larger twin bucket system will be needed, though the principle stays the same:

how it all fits together

This is the bucket system we made and you can see there's already some food waste in the top bucket and some juice collecting in the gap, as previously described.  So how does the juice get into the gap? Well, for that, you need to either drill holes in the base of the top bucket/container, or use a heated metal skewer (usual health and safety caveats apply here - in short, use some common sense):

drilling holes in the top bucket

Once your kitchen bucket system is ready, you need some microbe-laden bran, or BUGS bran as i call my own bran which i make for our family and friends.  Speak to your local council for a supply, check out ebay for Bokashi Bran, but be aware - some commercial producers of the bran don't put much in the way of microbes in the bran they sell and that can mean little to no fermentation takes place, which can mean problems arise.  The bran you get should smell strongly of salt and vinegar crisps, crossed with wheatabix - if it doesn't, it's likely that the bran producer is skimping on the supply of microbes to the mix.

Phase 1

Once you have your container/bin, sprinkle a layer of BUGS bran over the bottom. Don’t worry if some bran falls through the holes to the lower container.

Layer up all food waste.  This can be cooked or uncooked food, diary, citrus, bread, meats, teabags, coffee grinds, etc.  Remember to chop larger items, e.g. cauliflower stems, banana skins. A pair of scissors is a handy tool for this:

chopping waste to create a better fermentation action

Push the food waste down firmly to allow any liquid to drip through the holes in the bottom.  We recommend using a potato masher.  The objective is to push any air out of the waste and force excess liquid through the holes to the bottom gap:

mashing down = no air gaps

Sprinkle over BUGS bran to cover the surface of the waste and seal the container:

covering with BUGS bran

Repeat layering food and bran until the container is full.  Don’t forget to get as much air out as possibly by applying firm pressure.  You should keep your bucket assembly in the kitchen, where it's most convenient to get to:

stores tidily away

Phase 2

Once the container is full, it will need to be left to ferment for a minimum of two weeks.  But before storage, the liquid must be removed.  Lift out the inner container and pour the liquid into you compost bin or down the drain.  Putting this down the drain in summer can help keep your drains unblocked.

draining the liquid

During the process of compiling the waste the liquid from the decaying food will percolate through the bran, waking up the dormant microbes, which will begin to ferment the food waste. A layer of brown liquid will have collected in the gap between the containers.  On top of the liquid you may see white lumps floating – this is a product of the casein forming bacteria, which indicates the fermentation process is underway.

products of good fermentation

Once you've drained off the liquid from the bottom container, put the assembly back together and store out of direct sunlight for two to three weeks minimum to allow full fermentation.

storing outside to ferment

Whilst the full bucket assembly is fermenting for two weeks, you'll need another assembly of two buckets, prepared in the same way, to continue to collect your kitchen food waste.  Instead, you can do what we do and transfer the contents of your food waste into a larger sealable container, which you can then store for longer:

transferring to a larger container

As you can see, I have three larger containers, all full with fermented compost.  these larger containers I managed to blag obtain from a local company, who were throwing them out.  The benefit of transferring to a larger container is that you can store the fermented compost for months until you want to move on to the next stage.

If you've transferred your fermented waste to a larger container, you'll now need to wash out your kitchen bucket assembly with fresh tap water- I simply use a garden hose (and no soaps or detergents).

washing out your bucket system

and then add a layer of bran over the holes in the (cleaned) top bucket again, ready to go back in the kitchen:

getting ready to go again

Phase 3

After the fermentation phase is complete, dig a trench approximately 10” – 18” deep and spread the fermented compost across the base of this trench. 

digging a trench for your fermented compost

The compost will still look as it did when first added to the process, albeit slightly browner. Backfill the trench with soil and you're done! (remember to clean down your buckets of course - see above)

back-filling with topsoil

Leave in the ground for 8 – 13 weeks (depending on soil temperature / time of year).

Halfway through the 8 week in-soil phase, feel free to get a spade and go investigate - you should now see your very own worm nests!

worm nest!

Once the compost has been in the ground for the minimum required time, dig over the soil where the compost was buried and see the soil quality for yourself.

Over time, the soil will build into a rich, humic and highly nutritious growing medium - able to retain moisture, feed plants luxuriously and become a home to many healthy earthworms.