Moisture Content in CBD Flowers: Why the Listed Percentage Doesn't Tell the Whole Story

Sometimes you see a moisture content listed on a CBD flower and think that settles the matter. But that’s not really the case! I’ll explain what these two different measurements mean.

Things to remember

• Moisture content and water activity do not measure exactly the same thing.
• Moisture content indicates the total amount of water present, while water activity indicates the water available for certain reactions and microorganisms.
• To assess the stability of a CBD flower, water activity therefore provides particularly valuable additional information.

Moisture: the water contained in plant material

Moisture content refers to the amount of water contained in plant material, generally expressed as a percentage of the total mass.

A CBD flower labeled as having 10% moisture content therefore contains approximately 10 g of water per 100 g of material, depending on the analytical method used. However, not all of this water is necessarily available in the same way.

Some of it may be strongly bound to the plant’s components. Other parts may be more easily mobilized. This is precisely where the concept of water activity becomes interesting.

The moisture content primarily answers the question: “How much water does this flower contain in total?”

Water activity, on the other hand, indicates how much of that water is available to participate in reactions or be used by microorganisms.

What is water activity?

The term may sound technical, but the concept is quite simple. Water activity is generally denoted by “aw.” It ranges from 0 to 1 and measures the thermodynamic availability of water in a product.

The higher the aw, the morewater is available for certain chemical, enzymatic, or biological reactions. And that is precisely what interests professionals in the food and pharmaceutical preservation industries.

A flower can therefore have a certain total water content without all of that water being fully available. The AW thus provides additional information beyond the simple moisture percentage.

To measure this value, a sample is placed in a sealed chamber. The device measures the relative humidity of the air once equilibrium is reached, then calculates the water activity.

This is a physical measurement that differs from a simple determination of water content.

Why is aw important for conservation?

Available water, in particular, influences the ability of certain microorganisms to grow. As water activity increases, conditions can become more favorable for certain bacteria, yeasts, or molds.

Exposure to air, light, and temperature, as well asthe importance of packaging in the preservation of flowers and resins, also determine the likelihood of these microorganisms developing.

Why can a humidity level alone be misleading?

Now let’s suppose that two flowers have exactly 10% moisture content. You might think that they must have the same storage conditions, but that’s not necessarily the case.

The way water is distributed and bound within their plant matrix may differ. Consequently, their water activity may also differ.

This is a well-known concept in food science, where two products with comparable water content can have different water activities.

When it comes to CBD flowers, this means that a simple moisture content percentage doesn’t tell the whole story. It doesn’t directly tell you about the availability of that water or the product’s microbiological stability.

That is why some professionals prefer to supplement humidity measurements with an aw measurement.

Packaging can alter the balance

Once the flower has been packaged, its environment remains important.

Airtight packaging limits moisture exchange with the outside environment, but if the flower is packaged with an inappropriate moisture content, even high-performance packaging cannot retroactively correct the problem.

The balance between the flower and the air inside the packaging depends on storage conditions. Thus, a product stored in a warm environment does not behave exactly the same way as the same product stored at a moderate temperature. Light and oxygen can also contribute to the degradation of certain compounds over time.

Preservation, therefore, is a chain of factors: the condition of the flower at the time of packaging + packaging + temperature + humidity + storage duration.