C. 3a. How to make Actively Aerated Compost Tea

Aeration must be adequate to extract the maximum amount of soluble nutrients, and to maintain oxygen in aerobic concentrations in order to produce a tea high in aerobic bacteria and fungi, and with maximum extraction of protozoa and nematodes. The more diverse the community of microorganisms extracted and grown under aerobic conditions, the greater the disease suppression and the better nutrient retaining the tea will be. The greater the concentration of nutrients extracted, the more food there is to grow beneficial bacteria and fungi in the tea during the brewing cycle and after the tea is sprayed out.

It is CRITICAL to understand that tea must remain aerobic. If too great a concentration of food resources for the bacteria and fungi are added, the growth of the organisms will be so rapid, that they will consume oxygen more rapidly than oxygen can be added into the tea. The tea will go anaerobic, and then human pathogens can grow in the tea.

Any compost tea machine can be caused to go anaerobic, if too much microbial food is added, too much compost, and aeration is lacking.

Compost tea is used to add bacteria, fungi, protozoa and nematodes to the soil or onto foliage. Compost tea also contains soluble nutrients that feed the organisms in the tea and may feed plants. Use compost tea any time organisms in the soil or on the plants are lower than optimum levels. Chemical-based pesticides, fumigants, herbicides and some synthetic fertilizers kill the beneficial microorganisms that encourage plant growth, either in the soil or on foliage. Compost teas improve the life in the soil and on plant surfaces and help plants take-up the nutrients they require, and suppress diseases at the same time as building soil structure, and reduce erosion and loss of nutrients into drinking water. High quality compost tea of will inoculate the leaf surface and soil with beneficial microorganisms, instead of destroying them.

Given a good set of organisms (see Compost Tea Standards for what those numbers are), the following benefits can be brought about:

• Improved plant growth
• Reduced application rates of chemical pesticides, herbicides and fertilizers
• Reduced impacts of chemical-based pesticides, herbicides and fertilizers on beneficial microorganisms in the ecosystem
• Occupation of infection sites on the plant surface so pathogens cannot infect the leaf
• Improved uptake of plant nutrients through influences on stomata,
• Increased numbers of organisms on and around plants to compete with disease-causing organisms, reducing disease incidence,
• Retention of microorganisms in soil or on leaf surfaces, resulting in an increase in retention of nutrients,
• Increased plant nutritional quality,
• Production costs are reduced
• Reduced application of toxic chemicals, thus reducing run-off into lakes and streams,
• Reduced toxic impacts on humans and pets.

Step-by-step Approach to Making AACT

One, choose a compost tea machine that has documented ability to extract and grow the beneficial organisms from the compost you are using.

Here’s a list of brewers on the market in the US. We will be putting up a list of brewers from outside the US in a short period of time.

Demonstrated to Make Good Compost Tea, Grow Beneficial Fungi in the Tea Maker. These are not in any particular order!

1. EPM, Earth Tea Brewers – 100 ($3,500) and 500 gal Excellent extraction (composttea.com)
2. KIS brewers – 5 ($99) and 25 gal Good extraction, easy to clean!!!!! (simplici-tea.com)
3. Alaska Giant – 1 ($40) and 5 ($80) gal, good extraction, soaker hose (alaskagiant.com)
4. Ground Up – 50 gal and larger
5. Worm Gold (www.wormgold.com)
6. Compara
7. Sottilo - JAMSOT@aol.com Brewers made to order

Demonstrated to grow bacteria, and usually only anaerobic bacteria
SoilSoup – 6.5 gal ($400), 30 gal, 250 gal (soilsoup.com)
Growing Solutions – 25 ($1300), 100 ($5000) and 500 ($12,000) gal (growingsolutions.com)

Figure out the amount of tea you need to put out at any one time. If you can put out 5 gal today, and 5 tomorrow, and 5 the day after, why buy a machine that makes 50 gal? If you own 10,000 acres, ok, you need a big machine. If you own an acre or less, a 5 gal machine will likely do fine.

Read and ask questions on the compost-tea list serve (http://groups.yahoo.com/) put 'compost_tea' in the search box, relative to each brewer you are considering.

You need a tea brewer that the seller can document oxygen remains in the aerobic range!

Here’s a graph showing the type of information you need.

In this case, the red line is oxygen concentration in the water (in ppm or mg oxygen per L of water), and the green line is the active biology in the tea (micrograms of active bacteria and active fungi per ml of tea). When the organisms are growing the most rapidly, activity peaks (after about 16 hours in most brewers, although about hour 8 in small brewers).

The reason for the peak is that the microorganisms have maximized use of foods, and after that peak, their activity slows down, because they are running out of food. Activity usually stabilizes about 24 hours, so it is safe to take the tea out of the max aeration brewer and put it into a sprayer tank that has just re-circulation.

If the aeration is turned off, it typically takes some time for the organisms to use up the air, and plunge into anaerobic conditions. A truly stable tea would only slowly use up oxygen and go anaerobic, usually in about 5 to 6 hours. But if the tea is not in a stable condition, then when aeration is turned off, oxygen levels will plunge within mere minutes to low, anaerobic levels.

Two, find a GOOD source of compost! Ask the compost maker for documentation of the bacteria, fungi, protozoa and nematodes in the compost. If they don’t have the data, they have probably tested, and couldn’t show that their compost really is compost. Lack of data often means they can’t make the grade. You have to have the beneficials in the compost in order to make good tea. You may want to read over the compost section of this website to find out the desired levels of the different organism groups.

Three, decide on the foods you want to use to grow the beneficial organisms in your tea. The company you bought your tea maker from has a proprietary blend of foods that go with their tea machine, balanced already for the oxygen-use of that set of foods, and the ability of the machine to replenish oxygen during the growth of those organisms. It is critical that aeration be adequate. Alternatively, you can design your own tea recipe, but this will take some testing to make sure you are NOT adding too much food, and reducing oxygen, through the growth of the beneficial organisms, below aerobic levels. Foods that should be considered are:

• a diversity of sugars for bacterial growth, but realize that often the compost itself contains adequate bacterial foods to grow a great set of bacteria. Addition of more bacterial foods can just cause problems.
• Citric acid to help buffer pH to the right level, as well as feeding beneficial bacteria
• Cold-water kelp (higher in nutrients) to serve as a source of micro-nutrients (K, Co, B, etc, please check the label of the product you buy to make sure you are adding micronutrients you need. How do you know micronutrients are needed? A soil chemistry, or plant tissue test might be a good idea)
• Humic acids fro fungal growth, but realize that you want data to show you that this material can actually help grow fungi. Harsh extractants can make the humic materials very difficult for fungi, or anything else, to use.

Four, you need a means of transferring the tea from the tea brewer to the soil, or to the foliage of your plants. With small size tea brewers, pouring the tea into a sprayer works well. But with larger volumes of tea, you will need a transfer pump to move the tea into the sprayer unit. You need to talk to your tea machine maker and find out the testing that they have done to make certain that the pump doesn’t destroy the organisms in the tea as it is being transferred.

There is a tea maker on the market, clearly one not recommended by SFI, where the transfer pump kills about 50% of the organisms in the tea. So even though that company posts plate count data showing there is bacteria in the tea made by that machine, moving the tea out of that machine into your sprayer will kill about half the organisms in the tea. Please be aware of these kinds of snake-oil salesmen!

Five, you need a sprayer that will distribute the organisms evenly on the leaf surface. Typically any sprayer meant to apply pesticide will evenly apply tea organisms. The only thing that needs to be checked is that the sprayer re-circulates tea while the tea is in a large size tank (back-pack sprayers or smaller don’t need this, it typically doesn’t take hours to apply tea in small amounts), and that the pump used by the sprayer doesn’t kill organisms either. Talk to the tea machine makers about their lines of spray equipment.

Factors affecting Compost tea Quality

• Compost source – make sure it contains the organisms your plant needs
• Compost tea bag or container – the simpler the better, but opening sizes have to be right
• Brewing time – longer is not better
• Brewing temperature – make it right for the system the tea will be sprayed on!
• Water source – get rid of chlorine, chloramines, sulfur, other preservatives
• Extraction – the organisms have to be ripped off the compost, but not harmed in the process!
• Amount of tea applied to the soil or to the foliage – 5 gallons per acre for each 6 feet of foliage height, 20 gal per acre for the soil applications are the latest test results using EPM, KIS, BnBrewer, Clarke, AG, CT Brewer (NZ), and WormGold brewers.

The Pump

If you are going for the bigger machines, pay attention to the kind of pump on the machine. Did the manufacturer check to see if his pump kills organisms? Where are his data? Don't accept "trust me". There's a machine on the market that we demonstrated to the manufacturer that his pump to take the tea from the brewer into a holding tank was reducing numbers of fungi and bacteria by 50%. Keep that in mind, when buying something. How are you getting large volumes OUT of the tank?

Ease in cleaning is important.

Can you get to the bottom of the tank? Are there square corners in the pipes, knowing that in a month or so, that corner will be bio-film filled. It isn't right away that the problem develops. With the commercial Microb-Brewer, altered from the original design we tested at OSU, the pipes and pumps were changed to make the machine look prettier. The numbers on the changed machine were similar to the original, not-pretty design for the first couple of runs, but then, look out, the numbers dropped terribly as the bio-film developed. The manufacturer claimed that our methods had gone awry, that we didn't know what we were doing, because the numbers were coming out lower. It wasn't us, it was bio-film. But the manufacturer got mad at me. Stopped speaking to me all together. Called me all sorts of bad things.

SFI just tests the tea, we don't have to know why the numbers are coming out poorly. Usually I try to figure it out, and with the Microb-Brewer, we did figure it out. But not until after the damage was done. The Microb-Brewer is no longer for sale in the US.

Are there surfaces in the machine you can't see, can't get to to clean? Those places build-up biofilm. There's a brewer on the market that has discs in it, and you can't see, and you can't reach, the bottom sides of the discs. It is not fun getting the discs out to clean their bottom sides. Think about the time involved in cleaning. Most LARGE brewers should have a way to rinse the tank down as you pump the tea out. Talk to Bruce Elliott on this one. He developed the solution for this.

The compost container has to allow free movement of the compost.

Solid baskets that don't allow compost movement, that allow the compost to compact in the bottom, are going to cause you fits. Compost should be in bags, so easy-flow is possible. The EPM baskets are there to keep the bag of compost from twisting in the water flow, so the compost isn't constricted in that bag-basket design. But any other brewer with a basket has to have an aerator inside the basket, or the compost compacts, and goes anaerobic (happens at about 10 hours into the brew, so beware of the brewer that only has data for hours 0, 8, and 24)

Bubble sizes should be medium to large, not micro-sized.

Tiny, tiny bubbles are a bad idea. They shatter the fungal hyphae. Ask for the data showing good FUNGAL results. And please make sure the lab they are testing with uses decent methods.

No data? Don't buy the machine.

Only plate count data? Don't buy the machine. Ask what plate count data mean. Typically, you'll get gobble-de-gook as a reply. There are no data documenting a consistent relationship between plant growth and plate counts.

< previous next >