Quality and inspection
Moisture and water activity.
Moisture content measures how much water is in the product. Water activity measures how available that water is to microorganisms. They are different numbers and the second one is what determines stability.
The difference.
Moisture content is a percentage by weight, obtained by drying a sample. It tells you what fraction of what you bought is water.
Water activity is a ratio between zero and one, measuring the water available to support microbial growth. Sugar and salt bind water, so a sweet product can hold a lot of moisture and still be stable.
This is why dried fruit and honey keep despite being wet, and why a low-moisture product with unbound water can still spoil.
Why moisture content still matters commercially.
You pay freight on it. Coffee, pepper and cocoa shipped near their upper moisture limit are partly water by weight.
It changes on the voyage. Goods loaded wet lose water and arrive lighter, which is the most common phantom shortfall.
Wet goods in a warm container are where mould toxins develop, and that is a rejection at the border rather than a quality complaint.
Condensation inside a container, container rain, drips onto the top of the load and stains cartons in a pattern that looks like a leak.
What to specify.
Both, where the product is at risk. Moisture content protects the commercial position and water activity protects the product.
The method, because moisture figures obtained different ways are not comparable.
Measured on the shipped lot at loading, not on a typical value from a brochure.
For anything hygroscopic, specify the packaging barrier as well, since the number at loading is worthless if the pack lets humidity in.
Questions buyers ask.
Which number should I put in the contract?
Moisture content always, because it is the commercial figure and it is easily measured. Water activity as well for products where microbiological stability rather than weight is the concern.
Why did my cartons arrive stained on top?
Container rain. Warm moist air inside the box condenses on the cool roof and drips. It is caused by loading damp goods or damp dunnage, and desiccant and drier loading prevent it.
Is a lower moisture always better?
No. Over-drying costs the supplier yield and can damage the product, so the specification is a range rather than a minimum. What matters is that it is agreed and measured.
Read next.
Packing for a tropical voyage
Container sweat, mould, insects and crushing. Four failure modes that arrive as claims, and what stops each.
Weights and shortfall
Goods weighed at origin and at destination rarely match. Which gaps are normal and which are a claim.
Specifying the packaging
Left to the factory, packaging is chosen on cost. What to specify instead, and why.
What to test, and where
Which properties need a laboratory rather than an inspector, and whether to test at origin or at destination.
Weather and your order
Two seasons, both affecting drying, harvest, roads and loading. What to plan around.
Sourcing from Indonesia?
Tell us the product, the quantity and the destination. We come back with what it involves before anyone talks about money.