Basic Building Blocks, Nutrients and Growth Factors
What the Kombucha culture needs to survive
Stouthammer AH. quoted in Gottschalk, 1979. Note: These figures are representative but vary markedly among different bacteria and with different growing conditions.
The Kombucha culture has the following components available:
Lets look at each one of these components in more detail:
Sugar provides all the fuel needed to keep the Kombucha culture well and alive. Although sugar does include oxygen atoms, the oxygen required for the bacterial respiration does not come from it or the water. It has to be provided as free oxygen O2 from the surrounding air. The sugar used for preparing the tea is table sugar or sucrose, a disaccharide ("di" means two). Since the sucrose molecules are too large to be able to enter the cell walls of the yeast, they must be broken down first by enzymes into its components, the simple sugars glucose and fructose. Both are monosaccharides ("mono" means one). During a recent experiment using a spectrophotometer I found a significant quantity of protein in fermented K. tea. Initially I did not have an explanation for this finding. Later I interpreted this to indicate the presence of the enzymatic proteins required to break down nutrients into sufficiently small molecules capable of entering the cells of the microorganisms. One or maybe even two different enzymes are needed to break down caffeine and theophylline (see below). Another one would be sucrase (also called sucrose alpha-glucosidase) which cleaves sucrose into the simpler sugars fructose and glucose. In an article by Reiss (1987) he describes an experiment in which glucose concentration starts to rise steeply after about 4 days to reach a maximum after 9 days (see chart). This is a clear indication that enzymes are in fact breaking down the white sugar outside of the cells. Since enzymes are not getting used up in the catalytic process they would reach a maximum after a few days and would remain in the tea even after the tea has finished with fermentation.
Water is essential for life. Kombucha bacteria and yeasts must have water to be able to metabolize the food provided, to grow and to multiply. Water usually contains trace elements which vary with location. Some of these trace elements are needed by the Kombucha culture. Distilled water does not contain any trace elements.
Unfortunately, tap water often contains contaminents as well as undesirable microorganisms. Boiling the water for a sufficient length of time will usually kill the microorganisms. It will also remove chemicals like chlorine but not other contaminents.
Many but not all microorganisms require oxygen for their metabolic processes. There are several major categories: 1. Strict anaerobs, organisms that only metabolize without oxygen. This process is called fermentation. 2. Facultative anaerobs, organisms that can either, under the absence of oxygen, ferment foods into ethanol or lactic acid or, under the presence of oxygen, metabolize (respiration) food completely into CO2 and water. 3. Strict aerobs, organisms that must have oxygen to be able to metabolize foods. The yeasts in Kombucha are facultative anaerobs which will produce ethanol alcohol if there is no oxygen available. If there is oxygen available they will oxidize the available sugar into carbon dioxide and water. The acetic acid bacteria in Kombucha, are strict aerobes and require oxygen. They usually feed on the ethanol produced by the yeasts. However, they are also able to utilize other alcohols including glucose and may actually compete with the yeasts for the sugar. Since the zoogloea is floating on top of the K. tea, enough of the needed oxygen is provided to the acetic acid bacteria imbedded in its structure. The yeasts in the liquid down below are somewhat cut off from oxygen by the zoogloea and primarily use the anaerobic fermentative mode producing ethanol which in turn feeds the bacteria.
Black or green tea provides all the additional components and growth factors required by the Kombucha culture. It not only contains a number of important trace elements but also nitrogen compounds, carbohydrates, enzymes and vitamins. The stimulating components, caffeine and theophylline, belong to the purine groups which are required for building nucleic acids. Since these groups are used by the microorganisms, it could be assumed that the caffeine and theophylline in the tea are actually used up because they represent a source of nitrogen. What happens to the caffeine in Kombucha tea is a frequently asked question and this perhaps provides the likely answer. Total nitrogen in black tea represents 4.5% of the dry weight: 0.92% is found in soluble proteins, 2.51% is insoluble and 1.07% is contained in caffeine (for a tea containing 3.71% caffeine) and theophylline. According to one source (Abraham, 1995) green tea contains 5% caffeine and black tea only 2%. Green tea therefore provides more than twice the amount of nitrogen for the Kombucha culture. It is important to keep in mind that herbal teas do not contain these particular important nutrients and can for this and other reasons not be considered very suitable for making Kombucha.
GŁnther Frank (1994) already mentioned that Bing considers the purines - and caffeine belongs to this family - as providers of important nutrients for Kombucha. My assumption that the microorganisms in Kombucha do in fact break down caffeine to obtain critical nutrients is supported by an analysis performed by David Chappuis. He reported in a post to the Kombucha discussion group that he observed a reduction of caffeine by 25% during the first two weeks. (Feb. 28, 1998).
Here is the relevant part of a table he included:
I would expect that theophylline, the other purine compound in black and green tea, gets similarly used up during the "fermentation" process.