It works quite well to have it free floating, It really just depends on the brewer design. Some larger designs may not be able to supply enough oxygen through only one source. In that case another air supply is added somewhere else to improve oxygen levels. When this is done it just makes sense to add a source of microbes right near the soirce of oxygen. If you have a big clump of microbe fuel then the bag just keeps it right where the multiplying microbes can jump off and into the oxygenated water. Otherwise you risk perfectly good microbe potential going to waste in a less oxygenated area .
So mainly i have seen the bag method used as a supplement in larger brewers.
I have brewed in a 5 gallon with one good pump and see no need for a bag since by design the fluid is fully circulating every little bit. You really don't even need to strain it at the end unless you are using a sprayer or watering can with small holes.
Free floating compost could result in different strains of microbes dominating. Straining the slurry at the end may also remove many microbes and in particular fungi attached to the compost. Only one way to know, compare the two with a microscope or try both methods and do a field trial.
If you're planning on applying your compost tea foliarly, then the debris from the compost can easily clog your spray applicator. Other than that, I don't believe a bag is actually required.
"There is nothing, Sir, too little for so little a creature as man. It is by studying little things that we attain the great art of having as little misery and as much happiness as possible." - Samuel Johnson
I use 55 gal. barrels for compost/manure tea brewing I do not use bags to keep the solids separate I do, however, use a piece of muslin when syphoning the tea out of the barrels, the barrel end of the syphon hose has a piece of muslin clamped over it so no chunks get into the primer pump I use to get the syphon started.
I think the whole idea of making "tea bags" came from people thinking it was a bad idea to brew "cowboy" style for some reason.
I also stir my solids with a long wooden paddle I made, and I use the same batch of solids over and over, just adding a bit of new before I top off the barrels.
Then I cover them and let everything settle to the bottom, this way I can get nice "clean" tea for the plants.
I don't mean to this to sound b*tchy, but running pumps all the time doesn't seem especially sustainable.
For example, the 200l/m pump by Eco7 uses 280w ( listed on Amazon), which would mean around 48kg of carbon released each year per pump assuming mixed source electricity.
If the compost tea leads to a boost in productivity which in turn leads to at least 49g of additional carbon capture I get the value of it - i.e. 49kg of additional carbon storage over and above making compost tea without the airpump, and just giving it a stir every day - but I'm not fully sure that that works out.
Have you guys running the large compost tea setups looked at cost vs benefit?
I'm asking purely because I'd be interested in seeing the results of it.
I don't use air pumps, my barrels are set up to be stirred twice a day, the paddle seems to do enough aeration.
The paddle I made for this has several blades on a single vertical, these are angled so the liquid moves up from the bottom of the barrels with the stirring action.
When I pump tea from a barrel it is done with a hand pump, no electricity needed.
I use the tea on a rotational schedule so every week there are beds getting tea and beds getting only water ( use a water collection system for the gardens and orchard water ).
My teas contain; compost, minerals from out of date multi-mineral tabs and ground oyster shells, green sand and rock powders, manure and worm castings, with the bulk of the materials being compost and manure (also composted).
Most of the carbon in the left over plant material is then recycled through either the worm bins or in the hot compost heaps, these are then either used as straight soil amendment or made into tea for water born fertilization.
My cost is nil, since everything is made onsite and simply part of the recycling of nutrients.
The benefits are; healthier plants and larger harvest of produce and fruit.
As our systems grow, we will be creating more income through the sales of produce.
We have chickens on a deep litter system using straw as the floor medium along with some leaf material. This straw ends up well mixed with manure and we put that into a hot compost heap which reduces dangers of contamination through plant uptake of pathogens.
We have not moved into humanure systems as traditionally thought of, our septic system uses bacteria in a multi stage tank and flows out through a mycorrhizal-remediation leaching bed which tests results show is clean, non-contaminated out flow.