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Kombucha can be brewed even with tiny amounts of inocculate, such as the little bit of sediment at the bottom of store-bought kombuchas. Over 1-2 weeks, this can grow into an inch thick film covering the entire surface of the brew; a very striking accumulation of biomass. Where is the material for this biomass coming from?

It seems like most recipes for kombucha brew consist of:

  • 5.7% sugar
  • 0.7% black tea
  • 10-30% of a previous, "finished" kombucha
  • SCOBY (optional, the kombucha in the previous step is sufficient)

I can see how the sugar provides carbon, oxygen, hydrogen and energy. Of course, merely providing the elements is not necessarily sufficient, since often enough cells require specific compounds as well. But I'll assume the SCOBY community, in aggregate, is able to transform the sugar into every CHO compound it needs. However, what about nitrogen? The amount of tea seems minute, and tea seems like not a very rich source of protein/amino acids. Sugar doesn't contain nitrogen, and while dead SCOBY constituents from the initial kombucha can conceivably be cannibalized, the cannibalism cannot account for dramatic increase of SCOBY biomass because of conservation of mass.

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Short answer:

Nitrogen fixation (i.e, atmospheric nitrogen)

Longer answer:

Nitrogen fixation is the process by which atmospheric nitrogen is converted to forms usable by further biochemical reactions. Some bacteria are capable of nitrogen fixation (and some plants have symbiotic relationships with nitrogen-fixing bacteria); all the others rely on those species directly or indirectly to provide nitrogen.

The microorganisms involve in brewing kombucha tea are actually a collection of different species of bacteria and yeast. The bacteria that are found in kombucha tea include Acetobacter nitrogenifigens and Gluconacetobacter kombuchae, both of which are capable of nitrogen-fixation (and there may be others).

Molasses is also often used as the sugar source for kombucha, and molasses includes some nitrogen-containing compounds.

See the following review for more information:

Jayabalan, R., Malbaša, R. V., Lončar, E. S., Vitas, J. S., & Sathishkumar, M. (2014). A review on kombucha tea—microbiology, composition, fermentation, beneficial effects, toxicity, and tea fungus. Comprehensive Reviews in Food Science and Food Safety, 13(4), 538-550.

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  • $\begingroup$ I hadn't considered nitrogen from the air, wow! $\endgroup$ – Superbest Feb 6 '18 at 0:54

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