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Compost Teas and Extracts: Brewin’ and Bubblin’ Basics

by Rob Avis

Permaculturists everywhere are crazy about their compost teas and extracts. They have turned building compost tea brewers into a science and concocting the perfect tea recipe into an art. We love our compost brews too, and since we’re always getting questions about the compost tea process, we thought it was time to sit down and write a post about it. In this article we’ll explain the difference between a tea and an extract, discuss the best ingredients and recipes, and give you the step-by-step how-to for making your own compost tea brewer.

Get to Know Your Brews: Tea vs. Extract

What is compost tea? It’s a liquid made by both cold-brewing and aerating compost (or worm castings) in water, in order to extract beneficial organisms (i.e. bacteria, fungi, protozoa and nematodes). During the brewing process, these organisms are “fed” nutrients to rapidly increase their numbers and activity levels (source: It is then applied much like a fertilizer to soil, or to the roots or leaves of a plant. The process can take several days, and brewing itself has to occur over 24 hours.

A compost extract is different for a few reasons:

  • Instead of feeding the micro-organisms, the goal is simply to extract the microbes off of the compost or worm castings using the same aeration process.
  • Since no additional foods are fed to the organisms, no additional microbes are bred, and an extract can be made in 2 to 4 hours.
  • A tea has a shelf life of only 3-4 hours, whereas some experts claim an extract can last up to 2 weeks before things start to go off. (Teas have such a short shelf life because during the 24 hour brewing (feeding and oxygenating) process you have essentially bred more microbes per cc of liquid than would ever occur in nature. So, if you stop the aerator, the enormous number of microbes will consume all of the available oxygen and the liquid will go anaerobic. One of the easiest ways to tell if you have an anaerobic batch is by smell. If it smells bad, it probably is bad.)

Some believe that, because a tea has more time to brew, it makes a better amendment for your garden. In truth, there is increasing research demonstrating that extracts are as good as teas in terms of their ability to improve plant growth, health and soil fertility. (See bibliography download below for a list of studies on both). The exception is for foliar applications. Elaine Ingham of the Soil Foodweb explains that teas tend to “stick” better than extracts. Why? Because the microbes are metabolically active and growing when fed in teas. Some microbes will produce substances when growing that enable them to stick to surfaces. With extracts on the other hand, the microbes aren’t fed new food sources and are much less metabolically active, many would be dormant, thus very little stickiness). In addition, because there is much more biology per unit of water, it does a better job of coating the whole plant with beneficial microbes. It is this coating that protects the plants from disease.

Compost Extract & Tea Research Bibliography

Another difference between teas and extracts is that extracts tend to have higher biodiversity while teas have higher total microbial counts. This is because, in a tea, you are creating niche conditions (high aeration, specific foods, and agitation for 24 hours) that favour a more specific set of microbes, rather than in an extract, which supports the diversity of microbes that can exist in ambient conditions. The tea brewing process therefore knocks down certain spectrums of microbes while buttressing others. On the other hand, because extracts have a short brewing period and don’t get fed, the compost or worm castings you put in are the same ones you get out. In other words, if your castings or compost is lacking biodiversity, your extract or tea will too!

A Little Bit About Compost and Worm Castings

Compost brews, like so many things in life, follow this simple principle: you get out of it what you put into it. If you use amazing compost, you will get amazing teas and extracts. For our garden, I’m going to be using a worm casting tea from a local supplier, Dan Rollingson at Earthly Matters. The Soil Food Web Lab in Vulcan highly recommends these worm castings for brews. According to their detailed analysis of Dan’s castings — and from a Soil Foodweb perspective — they are pretty much as good as it gets! To date, we don’t know of anyone in Alberta producing commercial compost of high enough quality to use in brews. If you are in BC, Dean from Quality Compost makes a superb product, which is also Soil Food Web tested!

Let’s Build a Brewer!

Costs and Materials:

In total the brewer will have cost about $130 however I think you could build something of equivalent value for about $80 by shopping around on online. The main reason it costs so much was the high pressure, high volume pump. This is important as it aerates and stirs the extract or tea, which ensures that there are no dead spots (anaerobic) in the mixture.

Mark I

  • 4 black grommets that replace the bulkhead fitting — $1.00 ea
  • 1 x 5 gallon bucket — free
  • blue polyurethane hose — free
  • 1 barbed T hose piece — $2.00
  • high-pressure (3.9 psi), high-volume air pump, 65 litres per minute — $119*
  • drill bit to insert the grommet

Total ~ $129

Putting it all together

Watch the following video to see Rob explain the how-tos of building your own 5 gallon brewer:

Recipes (they taste terrible but your plants will love ’em)

5 Gallon Extract

To make a 5 gallon extract, fill your bucket 4 inches from the top and bubble air into the water for a few minutes to offgas any chemicals. You will preferably be using clean rain water, filtered city water (no chlorine), or river water. If you don’t have filtered water you can offgas the chlorine by letting your bucket sit out overnight as long as your town or city does not use chloramine. After you have bubbled your water for a few minutes, add 250-500 grams of compost or worm castings into the bucket and let it bubble for 2 – 4 hours. Your extract is now complete and ready to apply.

5 Gallon Tea

The compost tea is more complicated and requires a more thorough process, so we got permission from the Soil Foodweb Canada to post their recipe and procedure here (PDF).

Recommended Doses: How and When to Apply


Because we have brewed the tea without a tea bag, I would recommend that you filter the tea through nylon or equivalent. If you would rather skip this step you can get commercial tea bags from We do have some of these tea bags and I am going to try brewing tea/extract with and without them and look at both under the microscope to see which method gives a better product.


For the 5 gallon brewer, you can dilute with water at any ratio between 2:1 to 4:1. For commercial applications, the recommended dosage is determined by the farmer’s goals and the condition of the soil. Obviously the worse the soil, the higher the concentration needed. Generally speaking though, 1000 litres of tea can spray between 2–5 acres of land. To put that in perspective, my 20 ft x 20ft back yard would only need anywhere from 2–4.4 litres for the entire yard, depending on the application rate. That is a little less than 25% of one 5 gallon brew. The best thing about teas and extracts: as long as they are not anaerobic, you can’t overdo it!

Watering Can

This is, of course, the easiest way to distribute brews at a home scale. Because they pour out a lot of water at a time, you may want to increase the dilution rate to make sure you cover your desired area. I still recommend filtering your tea/extract first to prevent frustration.

Hand Spray Equipment

The spray is great for foliar and soil drenching. We use a hand sprayer at the Verge Headquarters because we don’t have much area to cover.


We cannot stress enough: you must clean your brewer before and after every brew! Our highly recommended tools: a bristle brush, some concentrated hydrogen peroxide, and warm water. As soon as you empty the tea or extract from the bucket, be sure to take everything apart and scrub it individually. If you don’t, a biofilm will form, which can wreak havoc in future teas and extracts.

Where Else Are Teas And Extracts Being Used?

Radioactive Waste in Japan:

There are now researchers doing trials with compost tea and radioactives on the soils in Japan. The trials will take about a year, but if successful, could be a real shoe-in for using biology to “clean up” radioactives, or at least rendering them plant unavailable. Only time will tell!

Anaerobic Bacteria to Lock-up Tailings from Mining:

Right here in our backyard, anaerobic bacteria is being used to form a biofilm (usually what we try to avoid in teas and extracts) over rock tailings from mountaintop-removal coal mining in the Elk River valley. Currently, the exposed tailing rock is oxidizing, which is leaching high levels of selenium into the Elk River, putting the fish at risk. To prevent this, the theory is that a biofilm could be applied to lock up the rocks from oxidation.

Additional Resources:

*You can also use an EcoPlus Air Pump — Commercial Air 5 Pump. You are looking for 65 litres per minute and 3.9 psi. Google “EcoPlus Air Pump — Commercial Air 5 Pump”


  1. Thank you very much for this explanation. The difference between compost tea and extract was an area I had been slightly confused about. Very timely information. I wonder if the recommended stirring methodolgy when making biodynamic teas, is somewhat related to improving the aeration of the mix?

  2. Rob,

    Excellent article and very much appreciated. I wanted to confirm the parameters of the air pump since that’s the most expensive piece.

    Are high-pressure (3.9 psi), high-volume air pump, 65 litres per minute correct? The reason I am asking is that the specific pump you listed seems to be a size too large. It looks like the Commercial Air 3 meets the specs you listed.

    Would air stones help deal with minimizing anaerobic zones? With a high volume pump, I would think it would be easy to run at least three stones to aerate and a hose to stir. I’m a newbie and have no experience with this equipment, but I thought I’d just throw it out there.

    Thank you in advance for any input on the pump & air stones! I look forward to trying both an extract and tea for max quantities and diversity!

    Best Regards, Kieran

  3. Desarae,
    Thanks for the comment. The biodynamic mixing breaks the surface tension which is what allows the air to dissolve into the water. To my knowledge though, the concentration of biology in biodyanmic preparations is much lower.


  4. Kieran,

    Those perameters are correct, 3.9 psi at 65 litres per minute. I would advise against air stones for two reasons.
    1) They will become plugged with biofilm after 1 or 2 uses which will go anaerobic and turn your tea off.
    2) Some research indicates that the small bubbles will shred the fungi.

    Use larger bubbles. It is mostly the action of breaking surface tension that dissolves oxygen into the water not the bubbles themselves.

    Hope that helps, thanks for the comments.


  5. Compost tea is probably a useful thing. But the matter is that it takes a lot of time to be prepared and nobody knows what kind of bacteria and funguses he grows. Together with useful bacteria there can live harmful fungi and other plant diseases in your compost. Instead of it you can take already done and guaranteed microorganisms which will work in the soil and on plants as fungicides and insecticides. Any harm, any lost time, any equipment. The whole you need is the biological preparation and water. To be sure visit the page 3 duby dot altcompostea dot x90x dot net. Believe me you’ve never seen something better.

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