One effective way to deodorize compost is to utilize effective microorganisms (EM) or microbial enzymes. These beneficial microbes help speed up the break-down of organic matter, which mostly smells bad while it is decomposing.

As the process gets done faster, odor can be significantly reduced from spreading around. The little microbes can help ingest the smell. When it's done composting, the smell will also be gone.

Brief Basic Understanding of Microbes

The microbes, short for micro-organisms, we're gathering are usually beneficial bacteria & fungi–not the bad guys. Some good EM that people have been using are:

  • Saccharomyces: found in beer yeast, bread yeast
  • Lactobacillus: found in milk, yogurt, drinking yogurt
  • Streptomyces: a fungi
  • Bacillus: found in hay, fermented soybean

These good guys are usually lactic acid bacteria, photosynthetic bacteria, yeast & other anaerobic and aerobic ones. Their size is about 4 micrometers & are much bigger than disease-causing microbes which are only about 1.5 micrometers.

Using EM for Reducing Smell

The good news is that once some of these microbes get established in your compost, they will also crowd out the other bad guys like pests or houseflies.

This means the odor-eliminating effect can last and be sustained for a longer period of time, not just for only 1 or 2 days, if we can keep this colony going on & on. With these microbes in the box, the composting time can also be reduced to about 4 weeks or sometimes half the time.

Using Eco Enzymes for Reducing Odor

The other application of microbial enzymes (eco enzymes or garbage enzymes) work in basically the same manner. These catalysts accelerate the decomposing process, which helps organic matter decompose fast and gets rid of the smell faster. Some commonly useful ones are:

Enzyme Purpose
Amylase accelerate break-down of starch → sugars
Protease protein (in meat)
Lipase lipids / fats (in oily foods)
Cellulase cellulose (in plants/veggies)
Phytase phytic acid

Let's see how we can put these microbes & enzymes to good use:

Way #1 - Using EM to Eliminate Odor

In some places, they sell the EM in pre-packaged bags in liquid or powder form. They isolate the good microbes in the laboratory with the most dominant microbe in the mix is LAB or lactic acid bacteria.

Some also call these bokashi bran. The problem people often complain about these is that this pre-made stuff can be too pricey in the long run.

Because when you use it up, you often need to buy again. Which is why some people dilute it to use or keep the lab EM in molasses for longer storage. But you don't have to buy these if you can find cheap alternatives around.

Other alternatives like sourdough starter, bread yeast or beer yeast also work well for this purpose. They contain a good amount of those Saccharomyces that help break down starch. The Lactobacillus, an amazing beneficial microbe, in some yogurt whey/drinking yogurt (like Yakult) can also be very helpful in eliminating odor.

Small note on Lacto
The Lacto part of the word doesn't really indicate that the food sources for the microbes must be milk-based. More accurately, it refers to the ability of the bacteria to lactate the carbohydrates in the food sources, that is turning it into lactic acid. Thus, creating a slightly acidic environment (lactic acid) that can shoo off other pathogens

One simple way to deal with the smell immediately is to mix sourdough yeast + water and spray the mixture around your bin. The advantage of this method is that it's fast, easy & cheap.

The disadvantage however is that it may work for 3-5 applications if you don't keep some of the juice for multiplication. Here we use the sourdough starter because there's yeast + lactic acid bacteria (the 'sour' guys) in it. Alternatively, you can use:

  • Instant active dry yeast/bread yeast/beer yeast
  • Yogurt whey (the liquid from yogurt making)
  • Drinking yogurt Yakult (with Lactobacillus casei)
  • IMO (indigenous microorganisms)
  • Pro-biotics for digestion

Here are the steps to make your own sourdough yeast EM for deodorizing:

Step 1: Use Lukewarm Water to Activate Microbes

Because they package the yeast or keep them refrigerated, the microbes may be in hibernation mode. To wake them up before using, use lukewarm water about our body temperature 37-38C (98.6-100F). Mix in about 2 tsp (10 gr) of yeast for 4 cups (1 liter) of water. Or simply, the ratio is about 1:10 to 1:100 (yeast:water). You can add sugar as food for the yeast.

Step 2: Let the Microbes Sit for 24 Hours

After about 30 min, if you see the mixture bubbles up then the yeast is alive & working. You can let it sit for some hours or 24 hours in a warm dark place to multiply in mass.

After that time period has passed, get some of that liquid concentrate (5 ml or 1 tsp) & dilute with 4 cups (1 liter) of water to spray around your compost box. If the bacteria are active, you will notice much less smell in 10-15 minutes.

Step 3: Store the Mixture

If you haven't used up all the juice that you made, refrigerate the rest so you don't need to keep feeding sugar to keep the microbes alive. To keep it at room temperature without refrigerating, add in about 1:1 ratio of brown sugar or molasses.

Step 4: Repeat

For the next usage, take some from the first concentrate. Mix in some warm water + sugar. Wait for the microbes to wake up and multiply. Then, we can use that stuff for spraying again. Trust me, it's super simple & mess-free. Now you can enjoy the effectiveness of effective microorganisms (EM) & a nice, smell-free compost bin in the house.

There's also one other way if you wanted a look:

Way #2 - Using Enzymes to Get Rid Of the Smell  

To make your own enzymes, you can use something like this:

  • 1 part sugar / molasses
  • 3 parts organic materials
  • 10 parts water

For example, in a jar we can mix in:

  • 1 part molasses
  • 3 parts kitchen scraps
  • 10 parts de-chlorinated water

The downside to this process however is that it is slower (takes about ~90 days for the mixture to fully break down. You can however scoop some out to use it early though). We need to wait for about 2-3 months to collect the enzymes. The cost however is cheaper & in many cases free. It's also a fun project to play with.

Let's see the first step we can begin with:

Step 1: Collect Some Kitchen Scraps

For the materials, you can use organic matter. For example: fruits, veggies, greens, beans, banana peels, etc. We don't really want meat, diary, fish or the high-protein stuff. Because the protein (with the nitrogen in its composition) while decomposing will give off a very unpleasant smell. Citrus peels, pineapple give the mixture the most fragrance.

Here we'll be using purple yam

Step 2: Mix In the 1:3:10 Ratio Ingredients

After getting some food scraps, mix them with a 1:3:10 ratio of molasses : scraps : water.

Mix molasses with water

Adding the yam:


After mixing the ingredients in, place them in shade or in partial shade.

Remember don't freeze the mixture because it will slow down the microbe growth. They like heat and warmth and some moisture. For the first 5-7 days, loosen the lid a bit to let the CO2 gas out so the built-up pressure won't break your jar. This is the time it will bubble up most vigorously.

Step 3: After 90 Days, Harvest Your Enzymes

After about 90 days, you can collect your enzymes. The end product will have a light alcohol smell with lots of good stuff like the amylase, protease, lipase & some organic acids.

Spraying these in will help your compost decompose faster & get rid of the odor. Depending on your need & the potency of the mixture, you may want to dilute it for more applications.

Extra Tips for Multiplying Pre-Made Microbes

Usually, we can add sugars, warm water or wheat bran to activate & multiply the initial number of microbes in the bag for longer usage. This is called EM2, EM3, EM4 and so on for the second and following generation.

Making EM this way is faster & the product can be applied immediately. If you don't have store-bought EM, you can definitely use the homemade mixture above for this multiplication.

To multiply 4 lbs of EM from the initial 2 teaspoon, we can mix:

  • 4 lbs wheat bran
  • 1 quart water (non-chlorine)
  • 2 tsp molasses
  • 2 tsp EM liquid/powder

But...Why Wheat Bran?

The wheat bran helps activate the microbes. As the bran is a carrier, you can replace it with many other cheap stable inert materials you find locally. For example: old newspaper, sawdust, spent beer grains, spent barley, rice hulls, powdered soybean meal, etc.

Why Use Non-Chlorinated Water?

We use non-chlorine water because the chlorine (or chloramine & chloramphenicol) in the water may kill off some of the microorganisms we're cultivating.

To de-chlorinate tap water, we can let it off gas outside in a bucket for 1-3 days without a lid or bubbling it for 90 minutes. The chlorine will then evaporate. Reverse osmosis water or carbon-filtered water also works fine. You could also try squeezing a few drops of lemon juice into the water, the vitamin C in lime helps de-chlorinate the water almost immediately.

Lukewarm water is great for our purpose because it wakes the microbes up after some time of hibernation. The temperature just a bit warmer than the water we use for baby shower should work fine. Or around our body temperature 37-38C (98.6-100F) is a favorite for the microbes.

Why Molasses?

The molasses is the yummy food/the energy for our little guys. In many places molasses is a waste by-product that is sold for very cheap. The sugar also helps activate the sleeping microbes.

When stored in molasses, the microbes can last for almost forever. Be sure to use black strap unsulfured molasses so it doesn't smell bad or kill our microbes.

You can replace molasses with other types of sugars or sugary juice like corn syrup, cane syrup, maple syrup, sugar cane juice or fruit juice. Balance the recipe out because molasses is a concentrated sugar. If you use other sugar types that are less concentrated, we may need to ramp up the amount. Finally, add in the pre-made EM. This can either be in liquid or powder form.

Enjoy the Multiplication

In about a week, we'll get more microbes from a small starting colony. You can use the final EM liquid to spray around & inside your compost. The liquid will have a light brown/orange color with a pleasant smell. We can also take some of inoculated the wheat bran to sprinkle around the compost.

Effective Compost Deodorizing

The smell from compost pile is caused by some bad microbes in an overly wet or low-oxygen anaerobic environment. In such as case, we can use the good microbes to counteract them.

Hopefully this post has given you some info & steps to get started. You'll absolutely love composting again as the bad smell might now be reduced. It will give you the most rewarding returns & great joy in gardening. Bye for now and see you around next time in the garden.

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