pH (potential of hydrogen)
pH
Japanese: pH（水素イオン指数）
A scale indicating how acidic or alkaline a solution is, ranging from 0 to 14 with 7 as neutral. Most fermented foods fall in the mildly acidic range of pH 4–6.
pH is a scale from 0 to 14 indicating how acidic or alkaline a solution is, with 7 being neutral. Below 7 is acidic; above is alkaline.
Most fermented foods are mildly acidic, at pH 4–6. Organic acids produced by lactic acid bacteria and yeast lower the pH, creating an environment hostile to spoilage organisms. This is a major reason fermented foods keep well.
Freshly prepared miso starts around pH 6, gradually dropping to about pH 5 as it ages. Tracking pH changes lets you read the invisible progress of fermentation.