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Water Activity Testing in cannabis product

How do we measure Water Activity on cannabis product?

Water activity (Aw) is defined as the partial vapor pressure of water in a substance § divided by the saturation vapor pressure (P0), also known as the standard state partial vapor pressure of water:

Aw = P/P0

Water activity can range from 0.000, which would be the measurement of a dry sample devoid of water content, to 1.000, which would be the measurement of pure aqueous water free of any bonding forces.

Water activity is measured by obtaining the saturation vapor pressure and the vapor pressure of water in the sample at a specific temperature. Common instruments take these measurements from a small sample of the product that is inserted into a water activity meter (the instrument labs have to measure water activity).

First, the meter measures the temperature of the sample, which directly correlates to the saturation vapor pressure (P0). Once vapor equilibrium is established, an infrared beam focuses on a small mirror in the instrument’s chamber to measure the vapor pressure of the water in the sealed headspace above the sample tray. This equilibrium vapor pressure equals the vapor pressure of water in the sample §.

These two measurements are then used to calculate the water activity (Aw). Accuracy can be determined by measuring calibration standards (salt solutions of varying concentrations) with known water activity values. KB Labs tests Water Activity in Cannabis products.*


Why measure water activities in cannabis products?

Measuring the water activity in a cannabis product is an excellent way to test how susceptible the product is to microbial contamination. The higher the measured water activity is in a product, the more freely water can be used by microbes as a food source or to support chemical and enzymatic reactions leading to spoilage.
In other words, the higher the water activity value, the more vulnerable cannabis products are to microorganism growth.


Very nice presentation of material.

For the visual learns in the group would you put up a graph of function

That might help show the nonlinear progression. I think that is where people get lost who don’t have food handling or grain production in there backgrounds.