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How to Make Compost Tea

Compost tea is an organic alternative to chemical compounds commonly added during commercial farming practices to improve soil health. Compost tea is a liquid produced by extracting bacteria, fungi, protozoa and nematodes from compost. The following information is supplied by the SOIL FOODWEB INSTITUTE based in Australia. They are the pacesetters when it comes to organic soil nutrition testing and practices. We are grateful to them for making this information available. References to the availability of products obviously refer to the local context. GAP Ministries have been implementing many of these practices with great success.  
The two key reasons to use compost tea are:
To impart microbial life into the soil or onto the foliage of plants 
To add soluble nutrients to the foliage or to the soil to feed the organisms and the plants present.

The use of compost tea is recommended whenever the organisms in the soil or on the plants are not at optimum levels. Chemical-based pesticides, fumigants, herbicides, and some synthetic fertilisers kill a range of beneficial micro-organisms that encourage plant growth. On the other hand, compost teas improve life in the soil and on plant surfaces. High-quality compost tea will treat the leaf surface and soil with beneficial micro-organisms instead of destroying them.
Why compost tea?
Compost tea production is a brewing process that is as simple to master as making a homebrew. Just like perfecting your homebrew, brewing compost tea may at times seem frustrating. However, if you concentrate on what you are doing and choose a suitable compost tea brewer that meets your specific needs, then creating a compost tea that will improve the health of your plants is relatively easy and well worth the effort.
If you want to introduce a highly beneficial group of bacteria and fungi, protozoa and possibly nematodes, buy good compost that has these organisms, and make Actively Aerated Compost Tea. There are a number of compost brewers available to choose from in the market. When purchasing a tea machine, you should ask the manufacturer to provide information on oxygen levels during the tea brewing cycle (the brewing process has to be aerobic) in addition to a standard food web analysis (molecular analysis of diversity, and total and active bacteria and fungi, and protozoa, present in the tea made under standard conditions).
The benefits of using a compost tea that contains ALL the food web organisms are:

What is in compost tea?
Compost tea contains not only all the soluble nutrients extracted from the compost, but also contains all the species of bacteria, fungi, protozoa and nematodes that are present in the compost. Not all the organisms in the compost, but representatives of all of the species in the compost are found in the final compost tea brew. It is therefore imperative that the compost you use in your brewer contains only the beneficial species of organisms required. Foods extracted from the compost, or added to the tea, grow beneficial organisms. Together, the beneficial bacteria and fungi growing on the compost foods, and on the added foods, result in a variety of many different species.
The method you choose to adopt when brewing is critical in ensuring your final brew contains the nutrients desired. In order to retain the organisms in the tea, brewing conditions must be closely monitored and maintained to produce the end product desired. The biological organisms that are active and performing a function will differ, depending on:
- the temperature of brewing,
- the foods added to the brew,
- oxygen concentrations in the brewer during production,
- the initial compost used: which species are present that can be extracted,
- the length of time tea is brewed.
Aerobic organisms are the most beneficial as they promote the processes that a plant needs in order to grow without stress and with a greater resistance to disease. To enhance this community of beneficial’s, the compost tea must remain aerobic (greater than 5.5ppm oxygen). Anaerobic conditions (below 2 to 4 mg oxygen per L for example) during brewing can result in the growth of some quite detrimental microbes and also produce some very detrimental metabolites. It is best to avoid extremely low oxygen concentrations during brewing. If low oxygen concentrations occur, brewing must continue until the organisms stop growing on the added foods, so that oxygen will diffuse back into the brew. The bacteria that cause human diseases almost invariably require anaerobic or reduced oxygen conditions in order to survive in competition with aerobic organisms. Only in reduced oxygen, or anaerobic conditions, can human disease-causing organisms out-compete the normal set of beneficial bacteria or fungi growing in soil, compost or compost tea. If you’ve done a good job choosing or making your compost, the compost will not contain any human disease organisms. The tea will not contain human pathogens if there were none in the compost.

What is the shelf life of compost tea?
The shelf life is short for a high-quality compost tea with those active organisms necessary to attach firmly to leaf surfaces and not be easily washed off. In the research that we have done with 24-hour brewing cycles, after just 6 hours without any aeration the oxygen levels are lowered by over 300 %. If the compost tea is not used within that time, you need to aerate, agitate and add more food to the tea to feed the micro-organisms.

Definitions of Compost Tea
- is a brewed water extract of compost,
- contains all the soluble nutrients that were in the compost,
- production methods include completely aerobic (AACT), using fermentative selective conditions (FCT), using long-term brewing conditions so that the tea returns to aerobic conditions after several weeks, as the smell goes away (LBCT), or using truly anaerobic conditions (NACT).
A true compost tea should contain ALL of the organisms that are present in the compost. Loss of certain aerobic groups when using FCT, LBCT or NACT methods leaves it questionable whether these products should even be called compost tea. They lack a large component of the biology needed to obtain the optimal benefits that are possible from compost or compost tea.

Information supplied by the  SOIL FOODWEB INSTITUTE

A simple way to make aerobic compost tea (left) and anaerobic manure tea (right). In order for any tea to propagate microbes exponentially, the minimum content of dissolved oxygen in the water must be greater than 6 ppm or 6 milligrams per liter.