A piece of thread was tightly wrapped around the middle of a "mother" and knotted in such a way that there was thread on top and on bottom of the zooglea submersed in the tea. The culture was prepared in the standard way. The thread remained on the zooglea for four generations.
Result: The thread on top was overgrown by four generations of "babies". The thread
underneath was still unattached but snug as before. There was no new growth visible under the
"mother" nor did the size of the "mother" change.
A standard Kombucha tea culture was prepared from the following ingredients: 6 quarts of water, 10 bags of black tea, 2 cups of white sugar, 2 cups of starter K.T. The cooled-off preparation was divided among three 2 quart plastic containers. No zoogloea was added to any of the containers.
Container A: NO OXYGEN. All air was pushed out manually and the opening closed with an airlock from a wine making kit. A spigot was attached at the bottom to be able to withdraw liquid for testing without letting oxygen in.
Container B: NORMAL AIR. A paper towel was attached to the opening with a rubber band.
Container C: ADDITIONAL AIR. A wooden bubble stone was inserted and attached to an aquarium pump. The opening of the container was closed with a paper towel.
| Test | Sample A | Sample B | Sample C |
|---|---|---|---|
| D a y 1 | |||
| pH | 6.0 | 6.0 | 6.0 |
| D a y 5 | |||
| pH | 5-6 | 5-6 | 5-6 |
| Taste test | sweet, no acidity | some acidity | some acidity |
| Zooglea | none | visible | too many bubbles |
| D a y 18 | |||
| pH | 3.65 | 3.30 | 3.01 |
| Taste test | sweet, mild acidity | very sour | very sour |
| Zooglea | none | 11 mm | <0.5 mm fragmented |
Comments: The first two pH tests were done with lithmus paper. It was very difficult to get a good reading since there is not enough of a color difference below 7 pH. The last pH test was done with an electronic pH meter which was calibrated with a 4.0 pH buffer. The measurements were repeated once.
The absence of oxygen in container A was verified by lowering a lit match after removal of the airlock. It was extinguished in an instant.
What surprised the most was the fact that the tea in container A tasted almost flat with little acidity even though it tested at pH 3.65. Sample B had the typical sour taste of regular KT. The pH difference between the two samples, on the other hand, was only 0.35. Although the number of H+ ions accounting for acidity increases exponentially compared to the decrease in pH value, the striking difference in sourness was unexpected. (Example: A solution with a pH of 4 has 10 times more acidity than one with a pH of 5. A solution with a pH of 3 is 100 times more acid than one with a pH of 5.) According to the literature, human taste sensation of sourness not only depends on H+ concentration but is also influenced by the shape of the molecules in question. Vinegar tastes considerably more sour than lactic acid with the same pH.
It has been suggested that one could cover the brewing container with a plate if a reduction in sour taste was desired. This would cause more lactic and less acetic acid to be produced. My experiment seemed to confirm this as far as flavor was concerned.
Since the acetic acid bacteria are known to be aerobic, sample A without the oxygen consequently produced no vinegar and no zoogloea. The observed acidity must have been completely due to other acids present. Lactic acid, for example, is produced as a by-product of fermentation under anaerobic conditions.
As Reiss has shown in his research, most of the acidity in K.T. consists of acids other than acetic acid. He found that K.T. grown under normal conditions after 10 days had only about 0.1 g/liter acetic acid, but 15 times as much gluconic acid and lactic acid. Another interesting result was that acetic acid leveled off after 10 days while the other two continued to accumulate. This would explain why I measured a pH for sample A that was lower than B by only a small number. Eliminating acetic acid in sample A had only a small effect on measured acidity.
Sample C showed the most acidity but the zoogloea was fragmented and not in a continuous
layer like in sample B. This probably was caused by the agitation of the surface because of the
bubble stone which probably prevented acetic acid bacteria from settling on the surface where
the most oxygen was available. It is not clear at this time why the acidity of this sample was
higher than sample B.
Last updated 1/22/96
Return to English Mainpage
