Bokashi is a process that helps change food waste and other organic materials into a soil amendment. This amendment adds nutrients to soil and improves its texture. It is different from traditional composting in several ways. Other names for this process include bokashi composting, bokashi fermentation, and fermented composting.

Nomenclature

The word "bokashi" comes from the Japanese language, written as (ぼかし). In Japanese-English dictionaries, the word is described as meaning "shading or gradual changes" in images, especially in woodblock prints. This meaning later included terms like "blurred spots" or "unclear areas" in censored photos. The use of "bokashi" to describe fermented organic matter has unclear origins. If both meanings are connected, possible shared ideas could be "change" or "fading."

The term "bokashi" is used in many languages to describe a food waste process. As a noun, it can mean different things depending on the context, such as the process itself, the starter material used, or the final fermented product. This variety of meanings can cause confusion. As an adjective, it describes related nouns, like "bokashi bin" (a container for fermenting food at home), "bokashi soil" (soil mixed with fermented material), and "bokashi composting," which is a term that does not make sense because composting usually refers to a different process.

Process

The basic stages of the process are:

• Organic matter is introduced to yeast, photosynthetic bacteria, and lactic acid bacteria. These microorganisms convert some of the carbohydrates in the material into lactic acid through a process called homolactic fermentation.

• The organic matter is fermented in a low-oxygen environment (more precisely, a microaerobic environment) for several weeks at typical room temperatures inside an airtight container. The lactic acid produced helps preserve the material, a process similar to how some fermented foods and silage are made. The preserved material is usually added to soil when it is ready, or it can be stored unopened for later use.

• The preserved material is mixed into soil that already contains naturally occurring microorganisms.

• When water is present (either in the preserved material or in the soil), the lactic acid gradually releases protons and becomes lactate, which is the acid’s conjugate base or ion salt. Lactate is an important energy source in biological processes. It can pass through cell membranes, and nearly all living organisms have an enzyme called lactate dehydrogenase to convert lactate into pyruvate for energy production.

• The soil, now enriched with lactate, is quickly consumed by the natural soil organisms, especially bacteria. This process causes the preserved material to disappear within a few weeks at normal temperatures. Earthworms often play a significant role by eating the bacteria, leading to soil with a texture similar to vermicompost.

Characteristics

The process is usually used for food waste from homes, offices, and restaurants because this waste often has a lot of carbohydrates. It is also used for other organic waste by adding carbohydrates to help produce lactic acid. Large-scale bokashi recipes in gardening often include rice, molasses, or sugar. Any waste with few carbohydrates can benefit from this method.

Homolactic fermentation can handle many more types of food waste than home composting. Items that are hard to compost, like cooked food, meat, fat, cheese, and citrus waste, are broken down so soil life can use them. Large pieces may take longer to ferment, and curved surfaces may trap air, so cutting them into smaller pieces is often recommended.

Pieces of waste are thrown away if they are already rotting or show green or black mold. These molds can grow harmful bacteria that stop the fermentation process.

Homolactic fermentation and similar processes without oxygen provide much less energy to cells than processes with oxygen. In homolactic fermentation, 2 ATP molecules are made when one glucose molecule (from breaking down carbohydrates) becomes 2 lactic acid molecules. This is only 1/15 of the energy produced by oxygen-based respiration. The process stops before all carbohydrates are used because the acid stops the bacteria. As a result, a bokashi bucket stays cool and does not heat up.

As a waste method, bokashi is special because it releases very little mass as gas. Composting, which uses oxygen, releases much of the carbon as carbon dioxide to feed microbes. Biogas production captures carbon as methane, a powerful greenhouse gas and fuel. Composting can also lose nitrogen as gases, but bokashi loses very little.

When fermentation starts, materials break down and release water as a liquid. Over time, this liquid becomes more than 10% of the waste by weight. The amount depends on the waste; for example, cucumber and melon flesh create more liquid.

This liquid carries proteins, nutrients, and lactic acid. To collect it and prevent it from stopping the fermentation, the liquid is captured through a tap, into absorbent materials like biochar or cardboard, or into a lower chamber. This liquid is called "bokashi tea."

Bokashi tea is used differently than compost tea. It works best when diluted and sprinkled on soil to feed the soil ecosystem. Dilution reduces acidity and makes it safer for plants. It also helps convert acid into lactate, which is food for soil microbes. Other uses, like using it to clean drains or feed plants directly, may harm plants or waste nutrients.

Household containers ("bokashi bins") usually hold 5–10 kilograms (11–22 pounds) of waste. This is collected over a few weeks. Each addition should be stored in a separate container to avoid opening the bin too often, which helps keep the environment without oxygen.

In gardening, larger batches are used. Silage technology may help if adapted to collect liquid. Industrial methods mimic large composting piles but compact and cover them tightly to keep oxygen out. Studies show these methods lose little carbon, energy, or nitrogen.

Bokashi is naturally clean in several ways:

• Lactic acid is a strong natural cleaner with known antibacterial properties. It is used in some toilet cleaners. As more lactic acid is made, it stops even the bacteria that produce it, slowing the process. Evidence shows it can kill Ascaris worm eggs in 14 days.
• A closed bokashi bin does not smell. It is only opened briefly to add waste or drain liquid, when it smells like pickles, which is less strong than rotting smells.
• A closed bin does not attract insects.
• Bokashi materials are said to repel animals in gardens.

Fermented bokashi is added to soil. The usual advice is to dig a trench in the garden, add the waste, and cover it.

Finding good spots for trenches in an established garden is hard. An alternative is a "soil factory," a small area where bokashi waste is mixed over time. Soil can be taken from here for use elsewhere. It can be any size, placed permanently or rotated, and protected from animals. Other materials, like compost or biochar, can also be added, blending bokashi with composting.

Another idea is to mix the fermented waste into a slurry and spread it on soil. This needs energy to mix but may help break down the waste fully, avoid disturbing deeper soil layers, and be less useful to animals. Repeating this could support a larger soil ecosystem.

History

The practice of bokashi is thought to have started in ancient Korea. This traditional method uses fermentation to break down waste directly in the soil. It depends on naturally occurring bacteria and careful burial to create an environment without oxygen. A modern gardening technique called Korean Natural Farming uses fermentation from local microorganisms, but it also includes other methods. In 1982, a Japanese scientist named Teruo Higa created a commercial version of bokashi called EM, which stands for Effective Microorganisms. This method became widely known around the world, especially for use in homes, and is now used in over 120 countries.

While it is agreed that EM begins a type of fermentation called homolactic, which creates a soil improvement product, other claims about EM have been questioned. Some debates focus on other uses, such as adding EM directly to soil or feeding it to animals. Others question whether the benefits of the soil improvement come from the nutrients in the fermented material or from the specific microorganisms in EM. Some scientists believe that the strong focus on microorganisms in EM has led to less attention being paid to the overall bokashi process and the roles of substances like lactic acid and higher-level soil life.

Alternative approaches

Some organisms in EM, such as photosynthetic bacteria and yeast, are not needed because they are first stopped by the dark and oxygen-free conditions of homolactic fermentation and then killed by lactic acid. To lower costs and increase production, people have tried methods like:

• Microorganisms collected by the user and tested for lacto-fermentation;
• Using lactobacilli alone, without other EM microorganisms. Good sources include acid whey from yogurt and sauerkraut juice;
• Alternative materials for growing microbes, such as newsprint;
• Homemade airtight containers for fermentation;
• Larger operations, such as groups of small farmers working together;
• Not adding microbes intentionally, similar to the original Korean method. The mixture may have a stronger odor because acetic acid, propanoic acid, and butyric acid form instead of lactic acid (see mixed acid fermentation). However, it still works well as a soil amendment.

Uses

The main use of bokashi, as described, is to take organic waste and change it into a material that improves soil quality.

When organic waste is used to help the soil instead of being sent to waste management systems, it reduces the costs of collecting and throwing away waste. In the UK, many local governments support this by providing financial help for bokashi starter kits through a program called the National Home Composting Framework.

Using bokashi also adds more organic carbon to the soil. Some of this carbon stays in the soil for a long time, forming a substance called humus, while other parts remain only as long as the soil is cared for with methods like planting plants permanently, not turning the soil, and using organic mulch. An example of this is the Ferme du Bec Hellouin in France. Bokashi could help communities change land from using chemicals to growing plants naturally, improve poor soil, and grow food in urban and nearby areas.

Bokashi can also help with sanitation, especially in treating waste from animals and humans. Products for cleaning pet waste are sold, but they sometimes do not warn about possible health risks. Treating human waste for use in soil has been studied a lot, often using biochar, which helps reduce smells and keeps nutrients in the soil. People being willing to use this method is a big challenge, but it may become useful in special situations like emergency aid, outdoor events, or temporary work areas.