Simple Compost Tea Brewer

How I designed and built compost tea brewer

Compost tea is a very effective natural fertilizer for garden and home plants. It can suppress fungal plant diseases. I have been using??compost tea in my garden for over a year??with amazing results. I have a 10 gallon outdoor??brewer that works great during summer. But during winter months I only need 1-2 gallons at a time for my indoor herbs and firing up "big boy", dealing with compost mix and cleaning up brewer under winter rain was too much. I??could not find a solution for indoor compost tea brewing, so I decided to improvise myself. I pre-mixed bunch of compost into small cloth bags and made a brewer out of small air??compressor and large mason jar with handle. It was amazing. I could have my compost tea twice a week and I did not have to??get dirty! Right about this time I was between hobby projects??and had some time in the evenings and weekends. I decided to take it to the market.

And I did it. After 3 months of experimentation - here is a final product.


And??highlights of the design process are below (mostly in pictures).

From personal experience I knew that my product must have following properties to be successful.

Questions that I had to answer during design stage

This is a test bed. While experimenting with recipes and aeration volume (amount of bubbles)??I was brewing 2-3 batches every day.??"Foaming" and "earthy smell" are both good indicators that everything is OK. But to you really need a microscope to check??variety and quantity of microorganisms.??

Good compost tea at 200-400x magnification is filled with life. In one drop of liquid you will see bacteria, flagella, fungi, protozoa and (sometimes) nematodes. These microorganisms provide nutrients to plants. In just a few weeks they will repair soil that has been treated with pesticides or chemical fertilizers.????

I have a friend who used 3D printing to design physical products before. I just followed his advise step by step. I read Design of Everyday Things, ??purchased 3D printer (FlashForge Creator Pro 3D) and spent couple weekends watching and following Autodesk Inventor tutorials. After 16??different prototypes??I ended up with non-threaded lid and vertical compressor orientation.

For the time being all plastic parts are 3D printed. After acetone bath the lid looks??nice and shiny. I can print ~100 parts a month, which is enough for now. I am getting quotes from injection molding shops for a mass production, but I still have much to learn about "plastic flow", "self mating parts", "sink holes", etc.



Picking up a container took over a month. I wanted a non-glass container with a handle. Mason jars looked the best but the largest I could find was 32oz, which I though was too small. I finally settled on 96oz clear plastic food grade??oblong (learned a new word on the way :). Made here in US. Interestingly many US companies will send you free samples if you ask.

This is how much??of compost and bacterial food goes into each bag. Fungal compost on the left (you can see it has a lot of "wooden" parts) and food for microorganisms on the right. Measured for 96oz of final product.

Figuring our the??recipe was fun. Bat guano, bird guano, earthworm castings, different manures. I called it "playing with shit". I learned enough to write a separate post about best compost tea recipe.??And I am not done yet :). Current kits use compost and bacterial food from KIS Organics.??

Figuring out packaging for tea bags also took a long time. Partly because of the long shipping time from Alibaba and Aliexpress and partly because "storage" experiments take long time. I tried water-soluble??plastics, filter paper, non-woven fiber, various fabric and nylon bags. Ended up using custom nylon bags for the compost and filter??paper bag for bacterial food.

Different fabric fibers under microscope. You need??at least 300 micron mesh size, so larger microorganisms can get out.

The full name for the compost tea is "actively aerated compost tea" and I needed a??way to aerate it. I got every type of airstone that I could find and run bunch of tests. Glass air stones give??smaller bubbles but they get??clogged very fast. I decided that large conventional air stone with slightly increase air pressure is better in the long run. No need to fanatically clean it after every batch. Just rinse it with water.


Most bacteria cultures die??fast in dry conditions. Airdrying is more lethal to soil microorganisms than freezing. I needed a storage container that can retain??moisture (water). But also beneficial bacteria and fungi need oxygen??to??breathe. I had to find out how many holes do I need to make in the storage??container. I couldn't find how much oxygen??does the compost uses, so I run tests myself at different temperatures. Now every container has scientifically established number of holes to keep moisture in but to let enough oxygen for a long storage??:)??

I needed a way to fill??these small bags with compost and bacterial food and I didn't want to spend $2000 for a real packaging machine. Trip to Lowes, motor with gearbox??from eBay and couple 3D printed parts and I have my own "horizontal packaging system" :).

Annya??designed label and logo??and I finally have something that I can try to sell.

This is what??350 feet of bubble wrap look like. Approximately 450,000 individual bubbles. If you pop one bubble a second it would take you 5 days to pop them all :)


Thank you for reading.