What is bokashi composting? Learn how to compost kitchen scraps with fermentation and enrich your soil through this accessible and low-maintenance method.
Like all well-intentioned gardeners, I believe that it’s my duty to compost all of the organic waste produced both in the garden itself and in my kitchen to build my soil’s health. However, I’ve always struggled with the mechanics and biology of a typical compost pile. Although sometimes I got passable results, I never seemed to have that enviously crumbly compost I’d see in magazines and on TV gardening programs.
But now, I get all of the nutrients from my kitchen waste into my garden with no fuss at all through the technique known as bokashi composting. What is bokashi composting? Bokashi, a word in Japanese meaning “fermented organic matter,” refers to a system of near-odorless composting that ferments and preserves organic matter until it’s put directly into the soil. The fermentation microbes used in this process are cultured onto dry substrate, such as rice or wheat hulls or hemp or kenaf fiber. This technique is so simple that it can be done in small gardens and urban gardens, in greenhouses and container gardens, and could revolutionize the recycling of organic matter.
What is Bokashi Composting, and Why It Works
Although soil-living microbes include many different types of organisms, bacteria is by far the most abundant group. Like all living organisms, bacteria must be able to harvest energy from the environment in order to grow and repair cell components, transport nutrients, move, and reproduce. Microbes typically digest carbon-containing compounds to harvest energy. Two of these digestion methods are respiration, an aerobic (with air) metabolic process, and fermentation, an anaerobic (without air) metabolic process. Respiration end products are inorganic: carbon dioxide and water. Fermentation end products are various organic compounds (acids, aldehydes, ketones, alcohols) and carbon dioxide.
By learning how to compost kitchen scraps and introducing fermentation bacteria as early as possible into your kitchen scraps and excluding air from the compost bucket, you’ll keep aerobic bacteria from taking hold and prevent the decomposition of the organic material. If the container were tightly sealed during the fermentation process, you’d need a release valve to prevent the buildup of carbon dioxide. But by leaving the compost bucket unsealed and covered, the carbon dioxide generated will prevent oxygen from getting into the bucket. The cover allows a small amount of carbon dioxide to escape.
Usually, in aerobic compost piles, large amounts of the atmospheric nutrients (carbon, hydrogen, and nitrogen) are consumed by respiration and escape into the atmosphere, leaving mostly lignin and cellulose, which can improve the texture of the soil but not its microbial and nutritional value. By fermenting the kitchen scraps, atmospheric nutrients will be retained and delivered directly into the soil — a great way to boost nitrogen without the use of fertilizer or cover crops. Once the fermented compost is introduced into the soil, which contains oxygen in the porous spaces, the normal process of decomposition will take place, and the vegetable scraps will disappear.
How to Compost Kitchen Scraps with Bokashi
Here’s what you’ll need to begin your bokashi composting process:
- A small (2- or 3-quart) container with a lid that’ll fit on your kitchen counter.
- A microbial inoculant you can sprinkle onto the kitchen waste to start the fermentation process.
- A 5-gallon bucket with a lid that you can empty your kitchen counter compost container into when it’s full (unless you produce very little kitchen waste). This will hold your composted waste while it ferments until you’re ready to dig it into your soil.
Note that if you use rice or wheat hull-based inoculant, your fermented compost will produce quite a bit of liquid, and that 5-gallon bucket will require a spigot at the bottom to allow you to drain off the excess.
Step 1
First, let’s learn how to compost kitchen scraps through fermentation. Once you’ve accumulated vegetable scraps; eggshells; small amounts of meat, egg, or cheese; prunings from house plants; wilted flowers; or citrus peels, put them into the kitchen counter container. Sprinkle a little bit of the inoculant onto the scraps each time you fill the kitchen container (about 1/8 cup inoculant per 2 cups kitchen scraps). This will keep the container from developing an odor, and the inoculant will begin fermentation. If the container fills every day, empty it into the 5-gallon bucket once a day, and sprinkle a handful of inoculant on top; repeat this each time you add a new layer. Keep the lids on the containers; they don’t have to be tight. Excess air will interfere with fermentation and cause decomposition; competing, non-fermentation organisms will become established; and the resulting compost will smell bad and not contain the soil-enhancing microbes you want.
After about two or three weeks, the microbes in the inoculant will have grown into the scraps. This process is temperature-dependent, so the microbe growth will take longer the lower the temperature is in and around the buckets. The only smell will be a slight yeasty scent from the fermentation, not noticeable if the container lid is on. The scraps will not look much different.
Step 2
Incorporate the fermented compost into the soil. In the garden, dig a trench about 8 to 10 inches deep and equally wide, spread the fermented scraps in it, and cover the scraps with the dirt you dug out. If you’re composting for your houseplants and don’t have access to a garden, you can use a pot or bucket of topsoil, dig the kitchen bin contents into it, and then use that inoculated soil for repotting or to dig in around the edges of potted plants. In either case, plant your flowers and veggies right into the fermented soil mix. By the time the seeds germinate or seedlings are established, most of the inoculated waste will have disappeared, leaving only the eggshells and tougher vegetables to break up over time.
If it’s winter and you can’t dig your soil, keep your buckets in a relatively sheltered spot, such as a shed or garage or under some tarps on the balcony. As the buckets fill, add more buckets. If the fermentation compost freezes, the microbes will just go dormant. You can dig it in when the soil is easier to work, and they’ll revive.
Why Ferment Your Compost?
The need for fermentation composting is pressing. We dispose of millions of tons of organic matter into landfills every year. This waste produces high levels of carbon dioxide and methane in the form of landfill gas. According to the Environmental Protection Agency, “municipal solid-waste landfills are the third largest source of human-related methane emissions in the United States, accounting for approximately 15.1 percent of these emissions in 2019.”
Bokashi can aid in solving this crisis by capturing carbon in the soil. Additionally, our soil is notoriously depleted, thanks to processes of removing topsoil and treating soil with harsh chemicals and inorganic fertilizers. These processes denude our soil of microbial life, which can lead to reduced nutrients in produce and the destruction of the link between plant roots and mycorrhizal fungi. Mycorrhizal fungi ingest glucose produced by plant roots and provide plant-available nitrogen and other nutrients. If the plants are fed nitrogen directly, the mycorrhizal fungi connection doesn’t develop, and any nitrogen not absorbed by the plants can drain into our rivers and oceans.
It’s vital that we feed the soil around us the richest, most nutrient- and microbial-dense foods we can to aid in rebuilding the earth around us.
Learn more about composting with bokashi as well as other apartment-friendly methods in Composting in an Apartment.
Explore another anaerobic process with a biogas digester in our podcast episode, How to Make Biogas at Home with a Biogas Digester.
John Wilson studied anthropology at Durham University in the U.K. before moving to Washington, D.C., and running a wholesale import business for many years. After selling his initial business, he found a deep fascination with soil science and health, and the microbial world. He began harvesting and growing microbes in the Blue Ridge Mountains and developed his bokashi microbial compost accelerant, Kenkashi, in 2018.
