Compost tea, a liquid solution or suspension made by steeping compost in water. It is used as both a fertilizer and in attempts to prevent plant diseases.[1]

Made by steeping compost in water for a variable period up to 5-days, then applying the liquid un-diluted as a spray to non-edible plant parts, or as a soil-drench (root dip), such as to seedlings, or as a surface spray to reduce incidence of harmful phytopathogenic fungi in the phyllosphere [3] Today, you can create compost tea at home.[4], as well as purchase DIY automated compost tea machines as well as compost tea brewing barrels are available commercially.[5] [6]
[edit] Anaerobic compost teas
These consist of controlled compost extracts made by adding finished, properly prepared compost to water and stirring the mix for 1 – 14 days. This process encourages the loosening of microbes adhering to compost and soil particles so they are transferred into the water itself. The notion that compost tea is a "brew" process is of only recent origin in the USA. Traditional compost tea (called compost extracts) developed in Europe and especially in Germany by microbial scientists from the late 1970s on, did not employ significant technological support to prepare solutions of compost with microbial counts as high as 1011 per ml. The mixing, or active aeration, was required after the introduction in the USA of molasses, sugars and other highly fermentable agents created fermenting, anaerobic conditions; as a direct result, it became necessary to take extra steps to maintain compost teas in an aerobic condition, to be safe and non-odorous. If the tea is properly made, it is a mixed concentrate of facultative and aerobic microbes, and presumed non-harmful. The US National Organic Program (National Organic Program) has strict guidelines on use of compost teas in USDA certified organic farming; research evaluated by a Tea Task Force did not support the idea that active vs non-active teas had any differences in terms of microbial hygiene, and therefore the need to protect the safety of organic consumers and the integrity of organic farming became necessary. For example, E. coli testing of compost extracts is strongly recommended and may be required under NOP; the levels should be less than 126 cfu ml-1.

Traditional European formula: Steep 1 part compost in 3 : 9 parts water, with optional additions of a handful of basalt-meal or granite-dust and seaweed powder, and stand at room temperature ( 20 – 25C°) for 3 – 24 days, with frequent stirring. Sieve through cheesecloth or a fine mesh screen.

[edit] Aerobic Compost Tea (ACT)
The use of air pumps or blowers to aerate or brew compost tea. A compost of high quality is added to aerated water at the rate from 1:4[7]. The water must have a sustained dissolved oxygen content of 6 ppm or higher to be able to support aerobic organisms and be considered an aerobic tea. Water may be warmed slightly but cooler water supports higher dissolved oxygen rates. By aerating the water the extraction and growth of beneficial bacteria, protozoa and fungi that were present in the tea is promoted. Teas are aerated from 12 to 48 hours depending what type of microbes are desired. A short brew of around 12 hours will favor the growth of fungi, while a 24 hour brew will favor the growth of bacteria and a long brew of 36-48 hours will favor the growth of protozoa. Some farmers will add small amounts of supplements that promote growth of these microbes. Molasses will promote the growth of bacteria while kelp and humic acid will promote the growth of fungi. Sometimes sphagnum peat moss or hay is added as a source of protozoa. After brewing is complete ACT should be applied to the field as soon as possible to ensure that the tea is applied to the soil when the microbes are most active. ACT is applied to the soil to boost populations of biology and increase the rate of biological activity in the soil. Sometimes ACT is sprayed on leaves as a disease preventative but the effectiveness of this application is debatable. It is important to use unchlorinated or dechlorinated water when making ACT, since chlorine will kill beneficial microbes.

Check the link shown below for a simpler method.

Taken full and completly from Doug Green's Simplegiftsfarm.com:

"You can jury-rig a tea maker from a 5-gallon pail and the most powerful aquarium pump you can find. My KIS brewer’s aerator has a one-half inch output valve and it is very powerful to keep the water roiling along.

Some writers recommend an air stone at the end of the aquarium air line but this produces lots of little bubbles and the objective is to have lots of big bubbles. (Little bubbles break up the fungi while big bubbles don’t.) So simply weight the air line to the bottom of the pail (a big old steel nut works really well). I’d put the steel nut on one end of the air hose and simply throw it into the pail (if you could keep it in the middle that would be ideal but again, this isn’t rocket science.)

So, we have a 5-gallon pail, an air source and a line to the bottom of the pail that is weighted down to stay in the bottom of the pail. Do try to ensure the air line stays in the middle of the pail to provide equal circulation through the pail so there are no “dead” spots in the water.

We add water to the pail. That’s the easy part. However, if you’re using municipal water that has been treated with chlorine you do have to let the water sit for at least 24 hours to outgas – and allow the chlorine to disappear. It helps if you leave the bubbler going for this time to roil up the water. Some municipalities use chlorine that is long-lasting and doesn’t disappear in 24 hours. If yours does this, go to an aquarium store and obtain a water treatment kit to break this chlorine down (you have to do this for fish so it does work for compost tea as well.)

We add food to feed the bacteria and fungi. Now this is where it gets interesting with every compost tea maker having their own recipe and each one developing different amounts or kinds of bacteria and fungi.

Recipe for Compost Tea

A simple recipe for a five gallon pail might include:

~2 tablespoons of molasses because molasses contains several different kinds of sugars
~2 tablespoons of seaweed emulsion or fish emulsion for the micronutrients (they’ll each give slightly different results)
~1 teaspoon of citric acid for the bacteria (you can toss in a couple of 500 mg. Vitamin C tablets instead or several tablespoons of lemon juice)

Note that this isn’t rocket science – you can adjust the amounts depending on your individual circumstances. No, you won’t get the same tea as the pro’s do but you’ll get something you can use and repeating it regularly all summer will give you a wide range of beneficial bacteria to add to your garden soil.

If you have hay, put a few handfuls in as well. Put your compost into a small bag (old socks are ideal) to make a tea bag. If you don’t have old socks (use the odd ones lost in the laundry):-) you can make a mesh bag out of old door screen. The trick is to contain the compost but allow free water flow through it.

Drop the compost/bag into the pail, turn on the aquarium pump and let her rip.

Come back 8 to 12 hours later and you have easy compost tea for your garden. 24 hours is recommended if you can let it brew that long. Do not let it go further than 24 hours or the good bacteria will start to die off and the bad bacteria will begin to grow.

Make the tea outside so that the microorganisms produced are the same ones needed in the garden. Cool weather will require organisms that thrive in cool weather and you can repeat the tea making when the weather warms up to produce organisms for warmer weather.

Use immediately and do not store!

Spreading the compost tea is also very easy in the home garden. You can use either a watering can or a regular backpack sprayer. Do NOT use a sprayer that has been used for chemical sprays. It will kill the bacteria and fungi. Even if you rinse it out, there is generally a residue left that makes it useless for organic spraying. Spray or pour compost tea everywhere. You should get it on plant leaves, on lawns, on vegetable gardens; wherever it lands, the organisms that will survive in those conditions will find food and will begin to do their job (eating the bad guys). In my small garden, I use a watering can. If I were putting it onto a lawn, I’d use a hand or backpack sprayer without the fine nozzle.

You can repeat this monthly or as often as you like. In a big garden with many perennials or fruit trees, I would be spraying compost tea onto plants and firing it all over the garden. A consistent approach to maintaining microorganism levels at their highest levels will produce the healthiest possible garden. "