Build a Compost Tea Brewer

Latest Update 2nd February 2020.

I use a 20 litre food grade plastic pail with lid to contain my brew.  Its big enough to make about 15 litres of compost tea, and I make it every month from freshly made compost to cover the whole of my vegetables and other annual plants.  In late Autumn and early Spring, I spray my trees and other perennial plants.

Here are the components used.  The electric air pump delivers a supply of air to the head of the T"shaped bubbler which is immersed in the tea at the bottom of the pail.  The supply hose passes through the lid before connecting it to the pump so the unit can be closed when it is in operation.

The compost is contained in a paint straining bag, tied with twine and suspended in in the tea just above the bubbler.

After 24 hours of aeration, the tea is strained using a paint straining bag so small particles of compost can't block the jet on my sprayer.

In winter I use a good quality aquarium heater (not shown here) to maintain the brew temperature at 24C so the microbes can multiply quickly.

The air pump (Hailea aco-208 available online) is designed for use in ponds, so the output is high enough to maintain aerobic conditions in the brew, and extract the microbes from the compost material.  *Note the second hole in the lid allows air to escape during aeration.

The pump is connected to a bubbler easily made from standard plumbing components.

The flexible tube is moulded in place by filling the rigid PVC pipe around it with silicone.  A length of 6mm wooden dowel can be pushed up the flexible tube to keep it straight and a plug of Blu-tac moulded around the tube at the bottom of the PVC pipe to keep it centred.  The dowel should be removed once the silicone sets, and the tube trimmed level with the bottom of the PVC pipe.

All the other components are a tight push fit so they can be dismantled for cleaning and sterilising between brews.  There are 8 x 2mm holes drilled in the top of each short tube for the air to escape into the tea.  Small stones are used in the bubbler as ballast to keep it at the bottom of the brew when in use.  They are also carefully cleaned between brews.

The air is free flowing with little restriction, and produce lots of bubbles and turbulence.  This is essential to prevent any dead zones forming in the brew where anaerobic nasties can multiply.