The color changes of the indicators were probably caused by the combined function of calcium hydroxide and chemical dye. A mechanism for the color change of the indicator scan be proposed as follows. Bromocresol purple is yellow at pH 5.2 (and lower) and changes to purple at about pH 6.8. Methyl red is red at pH about 4.2 (and lower) and changes to yellow at about pH 6.2. Since both chemical dyes were mixed with calcium hydroxide, they would be on the basic side and show the basic color initially. During fermentation, carbon dioxide produced by fermentation permeates into the color indicators within the packages of the closed system, and chemically reacts with calcium hydroxide to form water in the indicator film matrix. More CO2 molecules and some organic acid vapors (as minor contributors)permeate into the indicators and dissolve in the water, resulting in neutralization of the relative basic mixture. This pH change causes color changes in the indicator.