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The Foam is Not the Measure of the Tea

I was wondering if you would comment on the relationship between a “foamy” and a QUALITY compost tea? I remember reading that the foam is, for the most part, merely the result of aerated proteins, and is NOT necessarily a reliable sign of a tea overflowing with microbes. Worm castings contain such proteins, but a similar foaminess can be achieved by just adding some soy bean meal (a plant which contains many animal-like proteins). Is this, and not an explosion of bioslime, all that lies beneath the incessant focus on “foaminess”? What do you experienced brewers have to say in response to this epidemic of “foam hype”?


An obvious Compost Junkie junkie.

(from Denver)

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Apr 20, 2012
Foam is Not an Indicator of Compost Tea Quality
by: Dave

I love the way you phrased this question, it’s got pizazz (yes, that’s a real word).

I completely agree with you, foam is NOT the measure of the tea, but it can provide us with some information about our brew. As you mentioned, foam is typically an indicator of free proteins, amino acids, or carbohydrates1. If you’re brewing with vermi-castings, foam seems to be a given (i.e. dead worm bodies = protein source).

Is it a measure of quality?

I wouldn’t rely on it for my quality assessment. If foam meant quality compost tea, then all you would have to do is add some yucca extract during the brewing process and BAM, instant quality tea! (From my experience, yucca during the brewing process produces a lot of foam)

Instead, the two best means of assessing the quality of your compost tea are as follows:

  • Send a sample of your tea to a Soil Food Web lab for analysis
  • Use a microscope and assess microbial diversity/species/numbers

Does anyone else have any other methods they use to assess the quality of their teas (Haydn?)? If so, please share in the comments section below.

On this same note, you also mentioned the following, “foam…is NOT necessarily a reliable sign of a tea overflowing with microbes.” As far as I understand it, foam CAN be the result of microbial action, but it can also just be the result of agitating proteins. Have you ever whipped egg whites? What happened? They foam. So I would have to say, do NOT use foam as an indicator of tea quality, nor an indicator that your tea is ready for use.

Dr. Elaine Ingham recently said something along the lines of…the foam in compost tea is still not well understood other than it relating to free proteins and sugars.

I would really like to hear some input from the more experienced brewers in our Tribe. What is your experience with foam?


Ps – I’ve found cold pressed flaxseed oil to work well as a foam suppressant.

1The Compost Tea Brewing Manual by Dr. Elaine Ingham

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Jun 29, 2012
by: Chris Mac

Anyone looked at their foam under a microscope? Anything interesting?


Apr 10, 2013
by: Greg

I like to see foam but the real truth is when I look into my microscope. The microscope tells me when my tea is at a peak during the brewing process. I am starting my second year going organic and making my own brew. The results have been outstanding. No turning back for me.

May 15, 2013
Does no foam = epic fail?
by: Ruth

I have two questions: First, how far into the brewing process do you experinced brewers begin to see foam? Second, is it possible to have a quality tea and no foam? –Thanks in advance!

Jun 17, 2013
12 hours I see foam
by: Rose

I normally brew for 24 hours; the foam decreases by then.

Jun 17, 2013
by: Chris Mac

Depending on the recipe and when you add the “foods”, I see foam as early as 8hrs to as late as 30hrs. I think temperature is the biggest factor. In the shade at around 65-75 deg. our brews are at peak performance 24-36 hours.

Sep 29, 2013
reusing the worm castings to make more tea
by: Anonymous

I have a question: how many times can you use the worm casting to make more tea? I have been told several times but do not see it anywhere else on information about worm casting tea brewing.

Feb 03, 2015
Foam foam foam where are you?
by: eljun

I just noticed that after 12-14hrs of brewing I still don’t see any indication of foamy substance in my compost tea. What could have I done wrong?

I added brown sugars & honey since I don’t have unsulfured molasis available. Will this be okey? Thanks

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