Differences

This shows you the differences between two versions of the page.

Link to this comparison view

Both sides previous revision Previous revision
workshops:public:kombucha_fashion:start [2018/06/13 17:52]
127.0.0.1 external edit
workshops:public:kombucha_fashion:start [2019/11/14 11:01] (current)
Peter Musk [Growing Kombucha]
Line 101: Line 101:
  
 You can experiment with other food sources for the kombucha culture, too – keep the amount of sugar the same, and try coffee, or green tea as a nutrient source. Soluble plant fertilizers will also work (and produce a white pellicle), but contamination tends to be more likely. You can experiment with other food sources for the kombucha culture, too – keep the amount of sugar the same, and try coffee, or green tea as a nutrient source. Soluble plant fertilizers will also work (and produce a white pellicle), but contamination tends to be more likely.
 +
 +Further work on using alternative nutrient sources was carried out by Luis Quijano, a visiting student from the USA. Luis demonstrated that it is possible to use starch from a variety of sources, enzymatically digested with apha-amylase (available from home brew suppliers) according to manufacturers instructions as an effective food source. Potato starch proved the most effective, but all types (tapioca, chick pea and lentil) were effective. None of the starch treatments produced as vigorous growth as the standard recipe using sucrose, but this seemed to be a result of insufficient concentration.
 +
 +This work is a first step to developing a method for growing kombucha on starchy food waste (eg: stale bread) following enzymatic digestion.
 +
 +A summary of Luis' results can be found in this document: {{ :​workshops:​public:​kombucha_fashion:​kombucha_growth_experimentsjuly.docx |}}
 +
 +===The effect of container size and liquid volume===
 +It had been observed that the pellicle seemed to grow faster and thicker if the depth of nutrient medium was a minimum. ​
 +
 +This was more systematically investigated by Luis Quijano (see document above) with results showing that shallow containers did indeed seem to produce relatively more pellicle in a set time. The same volume of growth medium was used in containers of different dimensions to avoid any effect of nutrient depletion (ie: all the tests had the same amount of medium, and therefore the same amount of available nutrients).
 +
 +These results are in keeping with the known requirement of the bacteria for oxygen - bacterial growth happens at the surface, where oxygen is available from the air - and minimizing the depth means relatively more nutrients are available for growth. In deep containers, nutrients in the bottom layers feed the yeast, but not the bacteria making the pellicle.
 +
 +===Using Defined Growth Media===
 +A scientific approach to growing the bacteria responsible for producing the cellulose pellicle was explored by QUT Honours student Charles Liddell in 2018.
 +Charles began by isolating the organism from a sample of Kombucha provided from stock at The Edge, and used standard microbiological techniques of dilution plating to obtain clonal colonies of bacteria. Single colonies were selected, cultured and DNA tested. The organism resulting (//​Acetobacter xylinus//) showed no great difference from existng isolates, indicating that several years of culturing with selection for pellicle production had not altered the wild genotype. ​
 +
 +A defined growth medium was developed to grow the isolated bacteria, with additional nutrients provided to replace the contribution of the yeast present in '​wild'​ kombucha.
 +Further experiments were undertaken to explore the adoption of domestic substitutes to maintain the democratic principles of this project, and it was found that 0.1% w/v Vegemite (a yeast extract) could replace the more expensive tryptone and yeast extract used by Charles. All these cultures showed a much higher rate of contamination that the usual method, indicating that further investigation of adding extra acetic acid (vinegar) to the starter medium as a way of reducing pH and limiting contamination would be useful.
 +
 +Charles'​ defined medium recipe can be found in this document: {{ :​workshops:​public:​kombucha_fashion:​defined_medium_for_kombucha.docx |}}
 +This recipe uses less sugar than that used as standard, which resulted in thinner pellicles.
  
 =====Making with Kombucha===== =====Making with Kombucha=====
  • workshops/public/kombucha_fashion/start.txt
  • Last modified: 2019/11/14 11:01
  • by Peter Musk