Brewing Bokashi: Strengthening Student Skills in Dilution Theory through Fermentation Analysis

One of the basic microbiological techniques that students should master is that of using dilution theory to calculate the levels of bacteria in a fluid. This tip reports on using a rice water-milk fermentation mixture termed Bokashi as an easily implemented exercise in the basic microbiological lab to give students multiple opportunities to use dilution theory. Due to the shifts in bacterial community composition over time, a variety of microbes can be cultured using selective and nonselective media. Microscopic observation and the use of GEN III microplates to determine the collective phenotypic pattern of the mixture both give additional opportunities for students to hone their skills in bacterial analysis. Due to the decrease in the pH of the mixture over time, the notion of acid tolerance in bacteria can be explored and assessed using the microplate. By performing multiple rounds of serial dilutions and spread plating, students can practice their skill at using dilution theory several times over the course of the exercise