Table of Contents
Quick answer
Water activity (aw) tracks available water for microbes from 0 to 1. Salt lowers aw, which helps cured and dried foods resist spoilage.
A measure of available water in food for microbial growth, expressed on a scale of 0 to 1. Salt reduces water activity by binding water molecules, which is why salt-cured foods resist spoilage. Most bacteria cannot grow below 0.91 aw.
Water activity (aw) measures how much water in food is free for microbes, on a scale from 0 to 1. Salt binds water and lowers aw, which slows bacterial growth. Most bacteria struggle below about 0.91 aw, which is why curing preserves meat.
In Practice
Jam makers boil fruit with sugar to drop aw and shelf stable jars. Charcuterie targets specific aw after salt and drying so salami stores safely at cool room temperature.