Since the EM technology we use for EM bokashi was created by Professor Teruo Higa, I’ll just quote him on the subject. (The full text of the presentation is available at FutureTech, if you’re interested.)
...EM is developed using three principal organisms, namely Phototrophic
bacteria, Lactic acid bacteria and Yeasts. These three types are indispensable
for EM and even if other species were not included, these would develop
coexisting forms with other beneficial organisms in the environment. This
happens, as EM is not made under sterile conditions, but using simple technology
in many difficult environments. Thus, the EM of today consists of these three
principal types, which is subsequently enriched naturally by other species such
as filamentous fungi and Actinomycetes. The fundamental principle is that the
three principal species must be abundant in EM and the pH of the solution must
be below 3.5. This is the technology and if this combination is found, that
solution, made anywhere will develop the beneficial effects of EM.
...The technology of EM is based on holding the three principal species together at
a very low pH, when most species of microbes die.
...EM is now made in all continents from the three species I mentioned earlier,
which are isolated from the respective environments.
...This microbial solution can convert all wastes into very good fertilizers in a
There’s a lot more, of course, in various presentations, interviews, articles, and his An Earth Saving Revolution I & II, but the short answer is: EM is a combination of Phototrophic bacteria, Lactic acid bacteria and Yeasts grown in a low pH solution, used to speed the breakdown of organic matter.
EM is the core of the bokashi process, but not all EM is destined for a bucket. It’s used as a cleanser, in animal feed*, to reclaim radiation- and chemical-contaminated land...generally speaking, to correct imbalance in the natural environment on a microbial level. Or to create a desired one. As in a bucket full of kitchen waste.
Which is likely more than you needed to know. EM is the stuff you need to make bokashi bucket fermenation work—without it, you just get rot.
*And in non-US countries, as people-feed, too.