Bokashi and EM: what the science really says (fermentation, pathogens, gases, soil)

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Bokashi has its ardent supporters, who credit it with every virtue, and its sceptics, who see nothing more than a bucket of marinated waste sold with a miracle product. The truth lies somewhere in between, and it is more interesting than the slogans.

We make our own activator: all the more reason to be precise. Here is what published studies show, what they do not show, and what remains to be proven. If you are new to the method, start with our guide What is bokashi?.

What is well established: a fermentation that acidifies and preserves

In a sealed, firmly packed bucket, kitchen scraps undergo lactic fermentation, just like cabbage in sauerkraut or grass in silage. Bacteria convert some of the sugars into acids, mainly lactic acid. In published analyses, the liquid from household buckets had a pH of 3.5 to 4.9. At this level of acidity, the microbes responsible for putrefaction are held back: the waste is preserved instead of rotting.

This fermentation also uses up very little material. In a farm-scale trial, cut grass fermented under a tarpaulin lost only 3 to 6% of its mass in six to eight weeks, compared with around 60% for the same grass composted in open air. Nitrogen losses were 0 to 1.7%, compared with 10 to 16%. These figures come from a study involving Agriton, the manufacturer of Microferm: they are consistent with what we know about fermentation, but deserve to be confirmed by independent teams.

Bear in mind, however, that once buried, bokashi is broken down by soil life, and a good part of its carbon is released, here too, as carbon dioxide. Fermentation shifts decomposition; it does not eliminate it.

Key points

Bokashi is first and foremost a preservation method: it stabilises waste and retains its nutrients. The transformation then takes place in the soil.

What is really found in a kitchen bucket

A pilot study published in 2026 analysed the DNA of microorganisms in buckets from six households in Finland. The result is clear: lactic acid bacteria dominate at every stage, especially the genera Lentilactobacillus and Lacticaseibacillus, relatives of the cultures found in silage or kefir. Within the same household, the bucket's population often resembled that of the bran used: the activator does indeed inoculate the bucket.

Another finding: photosynthetic bacteria, often listed among the components of EM, were not found in the commercial brans analysed, and yeasts were scarce in the bucket.

Health and safety: what acidity does, and what it doesn't

Potentially pathogenic microorganisms were present, as they are wherever there are food scraps, but in very small quantities: on average 0.2% of sequences with one analysis method, 0.04% with the other. The authors conclude that household bokashi is probably not associated with an increased health risk. Reassuring, but six households is still only a pilot study.

That said, bokashi is not a sanitising process. On much more heavily contaminated materials, such as excrement, lactic fermentation reduces certain bacteria that indicate contamination, but is not sufficient on its own: the most resistant organisms, such as some parasite eggs, are not always eliminated. The bucket does not heat up and never reaches the temperatures that sanitise a well-managed compost heap. This is one of the reasons why animal droppings should never go in it.

The same caution applies to treatment residues. A small exploratory study, published in 2026, monitored buckets filled with citrus fruit treated after harvest: after six weeks, two fungicides had not disappeared and were increasingly passing into the liquid. Fermentation does not decontaminate waste.

Emy's tip

Put on gloves to empty and bury your bucket, then wash your hands, as you would after any work with waste or soil.

Effects on soil and plants: encouraging, but limited

• In the vegetable garden, a trial on spinach compared kitchen bokashi with compost and vermicompost. In the greenhouse, bokashi produced as much foliage as vermicompost; in the open field, the marketable yield of the second cut was significantly higher.
• In the nursery, a bokashi made from citrus pulp improved the germination of rootstock seeds (24% compared with 16% for the control) and the height of young plants, in a single greenhouse trial.
• Compared with compost, the advantage fades. In a pot trial, bokashi and compost made from the same waste gave very similar results: only one comparison out of sixteen was significantly in favour of bokashi.

These trials shed light on a practical guideline. At the time of burial, soil mixed with bokashi contained 288 mg of ammonium per kilo, compared with less than 5 in the control soil, a level that dropped back within a few weeks. Add the acidity and the salts, and you can see why you need to wait at least two weeks before planting.

The liquid, for its part, is rich in potassium but low in nitrogen: used on its own, it produced much less developed plants than a mineral fertiliser. On tomato plants, watering with highly diluted liquid produced stems around 13% thicker, but the difference in height was not significant, and only a few plants were tested. See Bokashi liquid: dilution, uses and limitations.

The role of EM: what is down to the microbes, and what is down to the material

In the field. A four-year trial in Switzerland compared live EM with sterilised EM, either alone or with agricultural bokashi. EM alone made no difference; with bokashi, a few inconsistent effects appeared, identical with live and sterilised EM: they came from the nutrients in the bokashi, not from the microorganisms. A pot trial likewise found no difference between bokashi made with and without EM.

In the bucket. Waste naturally carries lactic acid bacteria, and spontaneous fermentation is possible, but it is less predictable. A trial on household buckets compared live EM, sterilised EM and waste alone: total emissions did not differ, but methane was lower with live EM during the resting phase. The inoculant therefore has a measurable, but modest, effect on fermentation.

Our interpretation. The activator mainly serves to establish a dominant lactic fermentation quickly, before putrefaction sets in; the bran contributes by absorbing moisture and feeding the cultures. This is how we design our Bokashi EM compost activator: insurance for success, not a magic potion. On the other hand, the idea that EM permanently colonise the soil has not been demonstrated. For dosage, see Bokashi bran; for other uses of EM, our guide What science says about effective microorganisms sets out the facts.

Greenhouse gases: what we really know

The household bucket trial measured carbon dioxide, methane and nitrous oxide during fermentation. But no one has yet measured emissions from the second stage, in the soil or the soil factory, even though that is where most of the decomposition takes place. On an agricultural scale, the cut-grass trial calculated a footprint roughly ten times lower per tonne of material than windrow composting, but counting only the fermentation phase and fuel, and with the manufacturer's involvement.

Our position: bokashi probably limits losses while waste is being stored, but its full climate impact has yet to be established. To compare the methods, see Bokashi, compost or vermicompost.

What remains to be proven

• The destruction of weed seeds: nothing demonstrates it for the kitchen bucket. An agricultural trial under tarpaulin found no surviving seeds, but its authors consider the question worth investigating. In silage, a very similar fermentation, most seeds die within three to six months, but hard-coated seeds often survive. Two weeks in a bucket is much shorter: do not put weeds that have gone to seed in it.
• The effect on rats: no studies; well-buried bokashi is probably less attractive, but no more than that.
• Long-term effects on soil: no multi-year trials with kitchen bokashi.
• The superiority of EM over other lactic cultures: never demonstrated in a kitchen bucket.

Did you know?

Most scientific publications on “bokashi” are not about the kitchen bucket, but about fermented agricultural fertilisers, widely studied in Brazil, Indonesia and Mexico. Studies on household bokashi can still be counted on the fingers of a few hands.

In summary

Studies confirm the essentials: a lactic fermentation that acidifies and preserves waste with very little loss, and very few pathogens in the buckets analysed. The effects on plants are encouraging but modest, close to those of a good compost, and come mainly from the organic matter; the activator, for its part, helps the fermentation succeed. The absence of greenhouse gases, the destruction of seeds, the effect on rats and sanitisation all remain to be proven. It is a good tool for returning your scraps to the soil, without overblown promises.

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Other topics in the guide

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