When a buyer selects a dry product made from hemp seed — hulled hearts, protein flour or fibre — one of the first questions concerns shelf life and microbiological stability. The answer rarely comes down to a single moisture figure in the specification. A different metric describes storage behaviour far more precisely: water activity. It explains why one dry product stays stable for months while another, at nominally the same moisture, begins to mould or cake. Below we look at what water activity is, how it differs from total moisture, which thresholds matter for microorganisms, and what this means for incoming inspection, packaging and warehouse conditions.
Moisture and water activity are not the same thing
Total moisture (the overall water content) shows how much water is present in a product in total; it is determined, for example, by drying a sample and measuring the loss of mass. Water activity (aw) is the fraction of free, available water on a scale from 0 to 1. The key word is «available»: some of the water in a product is bound to proteins, starch and other components and effectively takes no part in reactions or microbial growth. Water activity counts only the water that is free.
The practical consequence: two products with equal moisture can have different water activity, depending on composition and how tightly the water is bound. Moisture and aw therefore convey different information, and it is the second parameter that indicates microbiological stability. Moisture answers «how much water in total», water activity answers «how much water is available for spoilage processes».
Water activity thresholds for microorganisms
Microorganisms need free water to grow, and different groups have their own minimum water-activity thresholds. These are standard reference points from food microbiology, given here as approximate ranges:
- Most bacteria need aw of roughly above 0.90 to grow; many pathogens (for example, Salmonella) around 0.91 and above.
- Yeasts can develop down to roughly aw around 0.88.
- Molds are the most resistant group — some grow down to about aw 0.70–0.80.
- Below approximately 0.60, microbial growth essentially stops.
Dry seeds, hearts and flour, if stored dry, usually sit well below these thresholds. That is precisely why they are microbiologically stable: they contain too little free water to support the growth of bacteria, yeasts or molds. Stability here comes not from preservatives but from the dryness of the product itself.
Sorption: why a dry product can «pick up» water
A product's water activity is not fixed once and for all — it is tied to the humidity of the surrounding air. A dry product is hygroscopic: it absorbs moisture from humid air, and as it does so its water activity rises. The relationship between a product's moisture content and air humidity at a given temperature is described by the sorption isotherm.
This has a direct practical consequence. A product shipped at a stable, low water activity can, under unsuitable storage conditions, gradually take up moisture and climb above the critical thresholds. This is why both moisture-barrier packaging and controlled relative humidity in the warehouse matter: the goal is to keep the dry product from drawing water out of the air. Packaging integrity and seal integrity are as important here as the initial dryness — a compromised seal opens the product to humid air.
What happens if water activity rises during storage
If moisture and water activity in the product do rise, several undesirable processes are triggered at once. The most obvious is mould growth: molds are the least demanding of free water and become active first. Following them comes a risk specific to plant raw materials — the formation of mycotoxins, secondary metabolites of certain molds. Purely physical defects appear in parallel.
- Mould growth and, as a result, the risk of mycotoxins in plant raw materials.
- Caking (clumping) of loose products — hearts, flour, fibre, cracked seed.
- The appearance of off-flavours and off-odours.
All these defects share one root — excess free water. So the basic set of measures against them is also common: dry storage, moisture-barrier packaging, seal and packaging integrity, and controlled temperature and relative humidity. It is worth marking the boundary of the topic: for oil, water activity plays a secondary role — there, oxidation dominates during storage, and that is a separate discussion. This article concerns only dry solid products.
How this ties into the food-safety system
Managing moisture is not a one-off measurement but part of a system. In the logic of prerequisite programmes (PRP) and the principles underlying food-safety standards, moisture control is built into several points of the chain. It begins at intake: controlling the moisture of incoming raw material prevents a product already prone to spoilage from entering production. It continues through warehouse conditions — maintaining the relative humidity and temperature at which the finished product does not take up water. And it is recorded in documents: microbiology and moisture appear on the test report for each batch.
Such a report is not a formality but a tool that translates reasoning about water activity into measurable values for a specific batch. It shows the buyer the actual figures rather than general promises of stability.
Takeaways for the buyer
Everything above adds up to a short practical checklist. It helps distinguish a product whose stability is confirmed by data from one for which only a single moisture figure is known.
- Request a test report for each batch with microbiology and moisture figures.
- Store the product dry, keeping it away from contact with humid air.
- Preserve packaging integrity and seal integrity until the point of use.
- Maintain controlled relative humidity and temperature in the warehouse.
The stability of dry hemp products is not a «default» property but the result of two conditions coinciding: an initially low water activity and storage that keeps it from rising. Understanding the difference between moisture and water activity lets the buyer ask the supplier the right questions and verify the answers against documents.
OOO «MAKOSH» is Russia's first full-cycle plant for the deep processing of hemp seed (SEZ «Uzlovaya», FSSC 22000 v6 food-safety system, which incorporates HACCP principles). Every batch of hulled hearts, protein flour and fibre is issued a test report with microbiology and moisture figures; product terms and prices are available on request.
This is what we make
Our own full-cycle plant in the Uzlovaya SEZ. Wholesale, EAEU documents, 0% THC.
Hulled hemp hearts (separated)
Protein over 30% · omega-3/6
Cold-pressed green hemp seed oil
Omega-6 : omega-3 = 3.5 : 1
Hemp protein flour
Protein 40–45 g/100 g
We’ll match a product to your production need and send samples with documents.