Editing Holy Bread (section)

== Preparation ==

-Prepare bromthymol blue solution ahead of time [0.1 g Bromothymol blue dye in 500 ml water(0.02%). Should be blue-green in color]. A red cabbage indicator dye would also work in this demonstration, if you care to substitute.

-Prepare a slide of active yeast, set up microscope

-Put indicator solution into the gas receiving vessel and into the 250 ml Erlenmeyer flask, enough that it is visibly blue green (may be different color depending on the acidity of your tap water!)

NOTE: If your tap water has a lot of dissolved minerals, or dissolved CO2, it may already be yellow – this is bad. Add a drop of NaOH to bring the pH back up so the bromthymol blue looks blue-green again. This way, the students get the full effect of starting at neutral, and with the addition of carbonic acid it turns yellow. We scientists can be tricky!