Stir Plate for Nutrient Teas??

[Ozmosis]

Greetings:

I'm new to the forum, and have decided after a 20 some year hiatus since I last attempted to grow (hydro flood and drain) that I would like to try my hand at an organic soil grow. Anyway I have a question. I have googled this topic in multiple ways and really haven't seen anything at all on it. I was wondering if you can make your nutrient teas on a stir plate. I was a dedicated homebrewer for a decade and have a couple quality stir plates that were used to grow up yeast cultures for brewing. Same concept as nutrient tea really. You feed the yeast a nutrient slurry and they use the food and oxygen to reproduce. You grow a small culture up to the size required for good fermentation of your brew. I'd like to know if I can use one to make nutrient/compost teas. As I have said I haven't really found any information online about this.

Basically my larger stir plates could spin a bar in a 3 gallon carboy if I wanted to go that big. The rotational speed can be controlled to determine how far down you draw the vortex. Just the act of circulating the water with a small vortex causes oxygen in the air to be exchanged into the liquid. Homebrewers doing cell counts have also found that you can spin crazy fast drawing the vortex all the way down to the stir bar and introduce fairly significant levels of oxygen from the air.

The benefit I see would be cleanup. I have multiple sizes of glass graduated flasks which would be easy to measure the tea volume, clean, and the stir bars all all silicone coated so they would be easy to clean as well. It would be nice to put the flasks and stir plates to good use again. Does anyone have any thoughts?

 

[mysticepipedon]

You can use them, but it isn't enough.

For brewing beer, you don't want the yeast to get much, if any, oxygen. You need to infuse oxygen into the brew for a tea, because you want to encourage aerobic bacteria, not anaerobic bacteria.

Get an aquarium air pump and an aeration stone — the more powerful, the better. You want the aerator to really roil the surface of the tea.

 

[Ozmosis]

Hi. Thanx for the reply. Actually I was quite into the science of brewing and competed on the state and national level in competitions. Food and oxygen are the limiting factors in reproductive capacity of a brewing yeast colony. When you are growing your culture the whole purpose of the stir plate is to introduce oxygen into the slurry, as well as to drive off the CO2 that the yeast are excreting. Without the stirring and air exchange the yeast would exhaust the O2 before the food and go to sleep within a couple hours. In addition when you brew your wort and innoculate it with the yeast for fermentation the first thing you do is drop a stainless air stone into the fermentor and intoduce pure oxygen from a tank into the wort for the yeast to consume at the beginning of fermentation. Pro brewers use an inline oxygen stone in the transfer piping. The oxygen stone at this point is easier than trying to constantly stir 5 or more gallons of wort. The yeast again reproduce at the beginning of fermentation and throw many of the esters found in the finished product. The yeast consume all the introduced oxygen during their reproductive cycle. It is once fermentation is complete that you do not introduce oxygen as it then becomes a source of staling or spoilage.

Some brewers experimented by putting airating stones in their culture on the stir plate and they achieved greater growth than in a slowly stirred sample, however if the sample was stirred at high speeds the rate of oxygen introduction and culture growth became much closer. Some argued that at thigh speeds you introduced osmotic stress into the yeast which does seem plausible. At any rate I was just thinking that at some point a homebrewer must have tried using a stir plate to airate their compost/nutrient teas. The true test, as in growing yeast cultures, is doing it both ways and looking at the culture under a microscope and comparing cell counts. I never invested in a microscope and relied on the postings of homebrewers who had them and did the cell counts.

Again my primary purpose is to not have to deal with a pourous air stone and tubing that will basically become a bed of bacteria after the tea is complete. In brewing you just dropped your stainless air stone into some sanitizer for a minute and you were good to go. My stainless air stone has extremely small pores and an air pump would be unable to push air through.

 

[MIGrampaUSA]

Hi. Thanx for the reply. Actually I was quite into the science of brewing and competed on the state and national level in competitions. Food and oxygen are the limiting factors in reproductive capacity of a brewing yeast colony. When you are growing your culture the whole purpose of the stir plate is to introduce oxygen into the slurry, as well as to drive off the CO2 that the yeast are excreting. Without the stirring and air exchange the yeast would exhaust the O2 before the food and go to sleep within a couple hours. In addition when you brew your wort and innoculate it with the yeast for fermentation the first thing you do is drop a stainless air stone into the fermentor and intoduce pure oxygen from a tank into the wort for the yeast to consume at the beginning of fermentation. Pro brewers use an inline oxygen stone in the transfer piping. The oxygen stone at this point is easier than trying to constantly stir 5 or more gallons of wort. The yeast again reproduce at the beginning of fermentation and throw many of the esters found in the finished product. The yeast consume all the introduced oxygen during their reproductive cycle. It is once fermentation is complete that you do not introduce oxygen as it then becomes a source of staling or spoilage.

Some brewers experimented by putting airating stones in their culture on the stir plate and they achieved greater growth than in a slowly stirred sample, however if the sample was stirred at high speeds the rate of oxygen introduction and culture growth became much closer. Some argued that at thigh speeds you introduced osmotic stress into the yeast which does seem plausible. At any rate I was just thinking that at some point a homebrewer must have tried using a stir plate to airate their compost/nutrient teas. The true test, as in growing yeast cultures, is doing it both ways and looking at the culture under a microscope and comparing cell counts. I never invested in a microscope and relied on the postings of homebrewers who had them and did the cell counts.
Again my primary purpose is to not have to deal with a pourous air stone and tubing that will basically become a bed of bacteria after the tea is complete. In brewing you just dropped your stainless air stone into some sanitizer for a minute and you were good to go. My stainless air stone has extremely small pores and an air pump would be unable to push air through.

You need a much stronger air pump. A small indoor fish aquarium pump isn't going accomplish what you're looking for when brewing an organic microbe tea. Think more like Koi pond size air pump.

Youtube how to make your own organic tea brewing bucket. Mine leaves a frothy head on top of the tea. It's that super saturation that kicks the microbes into over-drive.

 

[Ozmosis]

Yes, a stronger pump would make sense as it keeps a larger surface area in contact with the air/liquid exchange surface. I do appreciate your answers for sure. It is interesting learning the science/art of gardening. What I am really curious about is if anyone has tried a stir plate and/or compared the two methods. My proposed method is of course more expensive and therefore less cost effective, but in my case I already own all the equipment. It also is definitely easier to keep the system I am proposing clean and sanitized.
What I have found and read regarding compost teas from soilfoodweb, which is an international soil and soil biology consulting company is the following
"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."
So they are saying you need to keep the O2 levels above 5.5ppm. It has been measured that a stir plate growing brewing yeast in a nutrient solution which are consuming oxygen can easily maintain a level of 8ppm minimum of oxygen via the air exchange in the vortex. This seems like it should be sufficient to also brew compost/nutrient tea.

 

[Grapefruitroop]

Like the Big Guru said :
You need a minimum 0.05 CFM (cubic feet per minute), open flow of air and an optimum 0.08 CFM per gallon (US) or higher to make aerated compost tea (ACT)
http://microbeorganics.com/

 

[Ozmosis]

OK. I have decided just to brew an experimental tea using my stir plate and see how it goes. I am just making a small one 1000ml water, 2 Tbsp worm castings, 1/4 tsp molasses. I actually e-mailed Tim from Microbe Organics as referenced by Grapefruit and I had also previously read a lot of his postings. He answered and told me he thought it might be time consuming and not much benefit over other methods but to give it a whirl and see how it goes, so that is what I am doing. Interestingly he said he now uses lift brewers. I looked up some videos and they seem to use the air to create circulation in the tea and get much of their aeration from the vortex that is created which is exactly how a stir plate works by creating an air exchange in the vortex. I included a pic and shot a short video of the start of the tea which I will attempt to include with this post. I used a noisy stir stick. I'll have to dig around to find some of my smoother ones that make less noise. This one has a raised rib in the center which makes it bounce around more further agitating the solution.

 

[Ozmosis]

The tea is at 36 hours. I will call it good tomorrow. I've never really dealt with a brewed tea so I don't know what to make of it. It's really hard to gage anything without a microscope to look at it I guess. At 30 hours I stopped the stirring to smell the tea and it just kind of smelled earthy, like a damp forest. There were no off smells. Is this what compost tea smells like.? I then put it back on the stirrer to run some more. I am going to be making a bunch of teas using a combination of worm castings, Dr Earth Fertilizer, and I am likely going to pick up some Roots Organics Terp tea as well so this is my dry run at making a tea. When I stopped it at 30 hours I took about 200 ml of it, dilluted it 2:1 with water and put it on some basil I have in the kitchen window. The basil hasn't shown any adverse reactions so that is a good thing. I have a decent PH meter, but is it worth it getting a TDS meter? I know organic teas are not going to give you a comparable number to liquid ferts, but I was thinking it might be a good reference from one tea to the next if I am wanting to increase or decrease strength.

 

[Ozmosis]

Well since I have been unable to find a definitive answer I figure I might as well do some documentation myself. That way in the future anyone with a similar question who stumbles on this thread can benefit from my experience. When I e-mailed with Tim from Microbe Organics he said testing the solution with a dissolved oxygen meter would tell me if I was keeping enough oxygen in solution to keep the tea aerobic. He said 6ppm oxygen is what is needed.

So I purchased a Milwaukee MW600 dissolved oxygen meter. I set it up and calibrated it and my tap water out of the tap measured around 8.5 to 8.6ppm dissolved oxygen. I brought out my large 5000ml erlenmeyer flask and filled it to 4000ml (a bit more than a gallon) I added 5 Tbsp worm castings and 1 Tbsp molasses. I used a 70mm long (2.75") stir bar and set the speed high enough to draw the vortex all the way down to the stir bar. A vortex drawn partially down would cause some air exchange, but by drawing it all the way down to the stir bar introduces a lot more turbidity to the solution and should keep more oxygen in solution.

So far I have checked the tea once at +12 hours stirring and found the oxygen level at 7.6ppm. I will try to get another reading at +24 and +36 hours. So there was a reduction in dissolved oxygen of about 1ppm so far but it is still above the threshold to remain an aerobic tea. I have read that lift brewers can get 10ppm into solution but I have not seen it measured at different intervals during the brewing. It would appear the stir plate with full vortex is so far keeping sufficient oxygen levels but is less efficient that a lift brewer. I was not attempting to find a more efficient way to brew tea, just a way to brew on a smaller scale using equipment I already had on hand. I will update the thread when I have further information.

I have attached a pic of the vortex I am drawing in just water, and a short video clip of the start of the tea which shows the turbidity the vortex is introducing into the tea.

 

[Ozmosis]

I've got all the data. I pooched the last data point but not my fault. I got readings of the starting water + 12 hours, + 22 hours and I had planned the last reading at +36 hours. Unfortunately my power briefly went off and on overnight while I was asleep. My stir plate does not auto restart if power is removed and reapplied so I woke up to the sample not being stirred and I don't know how long it was off. I started it back up for the final 3 hours but the +36 hour reading is tainted and I included it with an asterisk only for completion.
Here are the dissolved oxygen readings of a compost tea maintained on a stir plate.
Initial: 8.6ppm
+ 12 hours stirring: 7.6ppm
+ 22 hours stirring: 7.7ppm
** + 36 hours stirring 5.5ppm (lost power and no stirring for several hours)
So yes, a stir plate can be used to brew aerobic compost tea. Even with the loss of power the data clearly shows that a stir plate drawing a full vortex down to the stir bar can keep enough oxygen in a compost tea to keep it aerobic. I will continue to make compost teas up to 4000ml in this manner with some confidence. Even with the flawed final data point the 5.5ppm was at the bare minimum to stay aerobic. This data jives with homebrewers who years ago claimed they could keep approximately 8ppm oxygen in a yeast culture on a stir plate. The drop in oxygen level would also seem to indicate that the tea was growing bacteria as something used up the oxygen while the stirrer was off.