This is going to be a long read because I'm a professional researcher, who writes 'technical' reports that are often difficult for some folks to 'wade through'. Often downright boring. Except the folks that are interested in the 'guts' of the given topic.
Compost tea has 'come a long way', especially in the last 15 years, and mostly (in my opinion) due to the efforts of Dr. Elaine Ingham .
I began my compost microscope training under an organic chemist research scientist back in 1954 and others followed. In this decade, have communicated with and studied Dr. Elaine Ingham's methods before she became Chief Scientist for Rodale - and attending her Soil FoodWeb microscope training seminars in Corvallis, Oregon to ensure that I'm using the latest information and techniques in my ROI Laboratory where I analyze the microbiology of soil, compost, vermicompost and tea for ROI's commercial clients.
Dr. Ingham's tea is called "Aerated, Activated, Compost Tea (AACT). She made excellent teas, because she is a scientist - and therefore follows scientific protocols. Her original Activator recipe called for a certain quantity of molasses (a composite carbon source) - which she later significantly reduced, because that much carbon developed only a very high bacterial tea. Of late, she has amended her recipe in favor of fungal foods.
ROI's brand of 'tea' is called Liquid Microbial Concentrate (LMC), with Microbial Starter developed from a blend of thermal compost and vermicompost - treated with a proprietary formula of Starter Activator, followed by controlled incubation techniques to develop a very high beneficial fungal component of the resulting Microbial Starter product - of which I am very proud - being one of the very best in the world. More costly than most, because it takes time and care to make it - but as in most all things, you only get what you pay for.
Aerobic hot batch compost to make LMC Microbial Starter is developed under very controlled conditions in the ROI compost research facility, to ensure that Nature's FULL microbial synergistic community exists in it. It's a 6-stage process that has been treated at each stage with LMC and a variety of fungal-food Activators, to ensure the highest quality possible.
The same care is applied in developing high-fungal earthworm castings for the Microbial Starter Blend. Most earthworm breeders 'don't have a clue' about proper earthworm diet (especially the mineral and V.A.M. components needed) to develop a high-fungal LMC Starter product.
There are a LOT of different commercial products 'out there' that purport to have sufficient beneficial microbes in them - but most don't, based on microscope inspection at 400x - and most of the microbes that I do find in such products are not at the right diversity. Buyer Beware!!
There are also many kinds of compost teas, and as many recipes for tea as there are tea machine (brewer) manufacturers - and people who experiment with a variety of recipes in their home brewers.
But let's be very clear about one very important issue. Unless you use and follow a brewer machine manufacturer's recommended brewing products and brewing instructions precisely, and are able to view the resulting tea at 400x with a light microscope, you're just guessing & hoping that the brew will finish-out OK.
As long as you're just guessing, you should NEVER sell your tea to anybody, because doing so could open you to serious liability consequences if someone were to become ill, or your product has a detrimental effect on their precious plants. Happened before and will happen again.
If a brewer is experienced, I'm not saying that their tea would, or even could make somebody sick. But supposition is what drives lawsuits. Unproven possibilities and probabilities can cost you your entire life's savings in a court battle to try and prove your innocence. That's life, in today's screwed-up world.
And it's not just looking at all the 'critters' growing and reproducing in your tea - but being able to recognize what you are looking at. Is it a 'good' guy or a 'bad' guy? If you grow 'em - you'd better know.
Could you recognize a deadly E.coli microbe strain if you saw one? That takes some training, which I highly recommend. Also, if you don't know how to use a light microscope - make every 'tea' batch EXACTLY under the same conditions, every time - and have EVERY 3rd batch tested by a microbial laboratory - until you are SURE that you produce a high-quality 'tea' product.
If you get a microscope, start by obtaining a copy of Dr. Ingham's book: "The Compost Tea Brewing Manual, 5th Edition", and her book: "Qualitative Assessment of Microorganisms". I also recommend her book: "Compost Tea Quality: Light Microscope Methods".
And not "just any" microscope will do. Must be one with a powerful light source. A good one can be purchased for $1,500 (with needed supplies) and the better ones cost in the $2,500 range. No, you don't need the REALLY best ones - because they cost in the $25,000 range.
Below is a list of the critical issues:
- QUALITY OF BREW WATER. EVERYBODY gets rain - using filtered rainwater is best, held under no-light and adequately-filtered air diffusion. Every other water (including well water) needs to be tested for pH (6.8-7.2 is best); and mineral content (such as iron) before use. ANY chlorine/chloramines/fluorides remaining in tap water will kill microbes. Do NOT use aquarium chemicals to adjust pH.
- ALWAYS fully-aerate brew water before ANYTHING is added into it. If not able to achieve a MINIMUM 8ppm of dissolved oxygen prior to ANY additions - DON'T BREW because your aerator has insufficient capacity. Why? Because ANYTHING added to the water takes up space - which reduces the capacity of that water to achieve and maintain the needed dissolved oxygen content needed for microbes to reproduce effectively. Monitoring the dissolved oxygen content during a brew is vital - because every microbe reproduced - uses more oxygen - and when reproducing billions of bacterial per hour, simply the reproduction cycle can drive a brew facultative and even anaerobic. Watch for excessive foaming and understand what that means to brew quality.
- Water TEMPERATURE is vitally important - and must be maintained constant, throughout the brew process. An aquarium heater will work IF properly sized to the tank volume. 85 degrees Fahrenheit (85F) is the target temperature prior to beginning a brew. Yes, cooler water will hold more dissolved oxygen, but will also decrease microbial reproduction.
- Use the highest quality Microbial Starter product you can buy (or make) that has Nature's FULL diversity in it - you cannot propagate a microbe species in tea, that is not present in the Starter. ANYBODY can make a high-bacterial brew - but such limited diversity is not very beneficial. Only a high-fungal tea is worthwhile - and based on my testing of Starter products on the market, most are close to worthless in terms of containing a high quantity of a large, actively-growing fungal population. Fungi DO NOT grow quickly in tea. Fungi are slow growing - AND there's a LOT of difference between growing existing fungi - and getting fungi to reproduce in tea. So in order to achieve a 1:.25 Bacteria-to-Fungi (B:F) ratio in a 24-hour brew - the fungal population in the Starter must have at least a 1:4 B:F ratio BEFORE the brew begins. I have not tested a commercially-packaged product yet, that had a B:F ratio of more than 1:.75. By my 'yardstick', that's poor for use as a Starter product - which is why I make my own Microbial Starter from 'scratch', by science-based methodology.
- Use the highest quality Microbial Activator you can buy or make) to feed microbes the energy (carbonaceous) and cell-building (nitrogenous) foods needed to coax them to reproduce efficiently - and select for only beneficial aerobic microbes.
If you don't use microbe food in the water to make tea, then chances are the microbes won't reproduce much, and you may be breeding the 'bad guys'. Food recipes for composting and/or tea brewing should select for beneficial microbes.
There is still a lot of misinformation about using molasses in compost and tea. Molasses is almost pure carbon. Sugar is an energy food, and has very little value in exponential microbial reproduction which requires nitrogen in PROTEIN form.
And of course you know that putting too much food in the water can keep the water from reaching the MINIMUM 8ppm level.
Yes, it takes a HIGH LEVEL of oxygen to reproduce microbes in vitro. More oxygen than it takes for fish to survive in an aquarium tank powered by a dinky airstone aerator dropped into a 5-gallon bucket. If the water does not contain MORE than 6 ppm (6 mg/l) of DISSOLVED oxygen, exponential reproduction of microbes will not happen, and you'll mostly breed anaerobic microbes, many of which can be pathogenic ('bad guys').
How does one determine if the compost tea has at least 6 ppm dissolved O2 in it? With a dissolved oxygen meter. A hand-held unit can be purchased for $300 - the best ones are in the $800 range. It is also necessary to monitor water temperature and pH in the tea.
And remember the primary issue. Compost tea should ONLY be made with the highest grade of AGED compost. NO tea will EVER be any better than the quality of the compost microbiology you start with.
If the compost you use to brew tea is not tea-quality compost, you're NEVER going to have very good tea. Why? Because there's more to tea than how many microbes are in the tea. The other side is DIVERSITY. How many DIFFERENT KINDS of microbes are growing in the tea. How does one grow a diverse population of microbes? By using a diverse set of feedstocks to make the compost.
Even if you started with tea-quality compost, if you just fill a sock or 400-mesh bag with the compost and drop it into a tank to steep - the microbes are going to stay put in the compost. Microbes make a sticky substance (exudation) so they stick to what they grow on; may have a 'suction cup' rear end; or the likes of 'tendrils'.
Unless the microbes get violently SHAKEN into the open water, outside the containment, exponential reproduction is simply not going to occur - even with the right kinds and amounts of foods - even if you brew at 8ppm+ for several days.
The word 'violent' pertains to a microbe perspective. The other word used is 'agitated'. As in forced away from where they were stuck. Forcing air and water THROUGH the bag that holds the compost is one way to achieve a successful brew - mainly because you would not be willing to sit at tank-edge and constantly squeeze a bag of compost in the bubbling water, for many hours.
But the best method is to not use a mesh bag, but add the incubated/soaked LMC Microbial Starter 'slurry' directly in to the agitating water bath. Much more efficient microbial extraction. Then you know by 'scope observation @ 400x: what the active/dormant population is, reproductive rates over time, nutrition, etc., etc.
How long does it take to brew a good batch of tea? Considering that all other factors are optimized, the GENERALLY-ACCEPTED minimum time for a high-bacteria brew is 24 hours. This brew is usually called a "concentrate".
Double the brew-time to 48 hours (which means adding more microbe foods of certain types, in certain amounts, at certain times) provides greater opportunity for protozoa and fungi to reproduce. This brew is called a "super-concentrate".
At this writing, the longest brew time that worked best for my purposes, is 72 hours. I call this "super-ex concentrate". The longest period of time that I have personally brewed compost tea? 8 days. That was to inoculate the alkaline water a newly-dug rainwater harvest pond in black gumbo 8.4 pH clay.
Brews longer than 24 hours can get complicated, because there are specific criteria which must be checked by electronic devices and a microscope, at set intervals; food levels must be controlled and oxygen must be maintained at correct levels continuously.
It is extremely important that such a brew NEVER be permitted to go anaerobic. Not even for a few minutes. In any brew, there are ALWAYS faculative microbes that can live in either a low aerobic or anaerobic environment, which will attack aerobic microbes if the solution becomes even slightly anaerobic.
This kind of commercial-level tea is extremely powerful. Many hundreds of times more potent than solid compost.
I'm not finished with trials at this writing, but it appears that a carefully-manipulated 72-hour brew is capable of curing a virus infection on a plant. Not yet documented in a scientific trial.
I'm working with a Texas County Agricultural Extension Agent in a trial of tomato plants that have been confirmed with Beet Curly-Top Virus. Texas A&M University has not released data yet from their lab tests, but already we've seen a 100% recovery rate of plants that had NO normal leaves - severe 'clubbing' - to almost full recovery with blossoms and fruit only two weeks after tea application. I'll provide a report after the A&M results have been published.
A lot of work is also being done to extend tea shelf-life. At this writing the accepted shelf life of compost tea in a sealed container, is 4 hours, and that's with only filling the container 50% - and leaving a 50% air space. Why? Because the high concentration of microbes in the tea rapidly consume the free dissolved oxygen in solution, which drives the liquid into anaerobic condition.
The more air in the container, the longer the microbes are capable of surviving. Many bacteria can simply "go dormant" when the oxygen level gets low - but many microbes (particularly fungi and protozoa) die because they are attacked by, and eaten by the faculative bacteria which suvive and thrive in anaerobic conditions.
This is a consideration when sending tea samples into a lab for analysis too. No matter how large the container, NEVER fill the container with tea, to more than 1/2 of capacity. ALWAYS leave a 1/2 air space.