Bokashi bran (EM activator): role, dosage, storage, and buying or making your own

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In a bokashi system, the bucket is the container, but it is the bran that does the work. This little brown mixture, with its yeasty smell, provides the micro-organisms that make your waste ferment rather than rot. Without it, there is no reliable fermentation.

What is in it? Why is it essential? How much should you use, and how can you tell whether it is still good? Here is everything you need to know about the activator, so you use enough without wasting it.

What is bokashi bran?

Bokashi bran, also known as activator, starter or ‘bokashi grains’, is a dry carrier loaded with fermentation micro-organisms. Most often, it is made from:

• wheat bran, the outer husk of the grain, which acts as the carrier: it is light, absorbent and offers a large surface area for the micro-organisms. Some manufacturers also use rice bran, spelt husks or sawdust;
• effective micro-organisms (EM), a blend dominated by lactic acid bacteria, which manufacturers combine with yeasts and photosynthetic bacteria;
• molasses, a syrup made from sugar beet or sugar cane, which feeds the micro-organisms as they get going;
• non-chlorinated water.

The damp mixture is pressed down away from the air and left to ferment for several weeks, like a small bokashi. The micro-organisms multiply, and the bran is then often dried so that it keeps. Our Bokashi EM Compost Activator is made this way, here on the farm, then lightly dried: it keeps for two years, and its production date is printed on the bag. To find out exactly what EM are and about the different products in the range, see our guide EM-1, EM-A, Microferm: choosing the right EM product.

Did you know?

Once dried, the bran stops fermenting: its micro-organisms go into a kind of dormancy. It is the moisture in your waste that wakes them up when you sprinkle the bran into the bucket. That is why well-dried bran keeps for months, whereas bran left damp changes and spoils more quickly.

Why you can't do without it

Your waste already carries thousands of microbes, including some lactic acid bacteria. But it also carries putrefying bacteria, especially on meat, fish and leftovers that are past their best. In a sealed bucket, it is a race: whichever take hold first set the tone.

The bran tips the balance the right way, in three ways:

• it heavily inoculates each layer with lactic acid bacteria, which acidify the environment from the very first days;
• it provides a little easily used food, thanks to the molasses and the bran;
• it absorbs some of the moisture on the surface, where contact with the air is greatest.

Without an activator, a sealed bucket of waste may smell of rotten eggs or drains rather than pickles. There are homemade alternatives, based on whey for example, but their results are less consistent: you then need to use more.

How much should you use?

The basic dose

Instructions and guides give different doses: one 20 ml spoonful per addition for some, two tablespoons for others, or one to two tablespoons per litre of waste. All these recommendations are of the same order of magnitude. We recommend:

• at the bottom of the empty bucket: one 20 ml dose on the grid;
• on each 3 to 5 cm layer of waste: a dose of 15 to 20 ml, i.e. about one heaped tablespoon or a small handful, spread over the whole surface;
• on the final layer, when the bucket is full: a double dose.

Our 20 ml Measuring Spoon takes the guesswork out of it. The full method is described in our guide Starting your first bokashi bucket.

When to use more

• Meat, fish, cheese, eggs: these protein-rich leftovers are the most delicate. Be considerably more generous on these layers. Our guide What waste can go in a bokashi explains the precautions to take with them.
• Very wet waste: melon, watermelon, squeezed citrus fruit, salad, leftover cooked vegetables.
• In winter, when the room is cool: the micro-organisms work more slowly.
• At the first sign of things going wrong: a smell turning unpleasant, coloured patches of mould. A good dose of bran followed by careful pressing down will often put things right. Our guide Mould in bokashi will help you tell good from bad.

What if I use too much?

Too much bran does not harm fermentation: it is simply wasted, and it adds a little dry matter to the bucket. If in doubt, it is better to use a little too much than too little, without burying each layer under a thick crust.

As a rough guide, allow 2 to 6 kg of bran a year for a family of four: a 1 kg bag therefore lasts roughly two to six months, and closer to six months for a two-person household. With a very generous hand, or lots of meat, fish and wet leftovers, it may last only a month.

Key points

The right dose: about 20 ml of bran per 3 to 5 cm layer of waste, more for meat, fish, wet waste and in winter. If in doubt, a little more rather than a little less.

How to tell bran is in good condition

A good activator is recognised first by its smell. It smells of yeast, bread, beer or has a sweet-and-sour note, sometimes slightly alcoholic. It is dry or barely damp, brown in colour, and crumbles easily. A few filaments or a light white bloom are nothing to worry about: they are a sign of fermentation.

Replace your bran if it shows any of these signs:

• it smells mouldy, musty or rotten;
• it no longer smells of anything at all: the micro-organisms are probably too weakened;
• it has green, blue or black mould;
• it has become damp and sticky, or has formed compact lumps.

Dubious bran should not go into the bucket, where it could set off a bad fermentation. You can, however, scatter it on your garden composter.

Storing it properly

• In an airtight container: its original bag tightly closed, a box with a lid or a jar.
• Somewhere dry: moisture is its main enemy, as it restarts fermentation inside the bag.
• Away from light and heat: a cool cupboard rather than the windowsill or the top of the oven.
• Not for too long: dried and well stored, bran keeps for one to two years depending on the manufacturer. Ours keeps for two years from the production date printed on the bag; for homemade bran, allow about a year.

Emy's tip

Always scoop out the bran with a completely dry spoon and close the bag again straight away. A wet spoon or a bag left open by the sink is enough to let moisture into the whole pack.

Buy or make your own?

Buying a ready-to-use activator is the simplest option when you are starting out: the fermentation has already been mastered, and the bran is dry and consistent. This is what we recommend for your first buckets.

Making your own bran becomes worthwhile once you use bokashi regularly, or share it with others. You need wheat bran, EM-1, molasses, non-chlorinated water and three weeks of fermentation without opening, followed by drying. Our Kit for making your own Bokashi & Compost activator brings the ingredients together, and our full step-by-step recipe is in our guide Making your own bokashi activator.

Finally, if you are wondering what micro-organisms really bring beyond getting fermentation started, our guide Bokashi and EM: what the science says sets out the facts without exaggeration.

In summary

Bokashi bran is wheat bran fermented with effective micro-organisms and molasses, usually dried so that it keeps. It is essential, because it inoculates each layer with lactic acid bacteria and gives fermentation the head start it needs over putrefaction. Allow about 20 ml per 3 to 5 cm layer, more for meat, fish, wet waste and in winter. Good bran smells of yeast or is sweet-and-sour; if it smells mouldy or of nothing at all, replace it. Keep it dry, cool, away from light and tightly closed: ours keeps for up to two years (production date on the bag), homemade bran for about a year.

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Other topics in the guide

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