Dried fruit and nuts are sometimes consumed together as a product named: “trail mix”.  That’s not the only reason these two products fall in the same category on this page.  Dried fruit and nuts are both natural products that normally undergo post-harvest processing before they are sold to consumers.  Moisture mistakes for both these products are similarly painful: too much water causes mold; too little equates to lost profit, not to mention quality problems.

Today’s Moisture Methods

The majority of growers or producers use moisture content to calculate if tree nuts or dried fruit are too “wet”.  This causes problems.  First, the moisture level that supports mold growth is different for every kind of nut or dried fruit.  Secondly, loss-on-drying moisture is not a very accurate method for measuring moisture levels – the answer you get depends on the method you use.

Standardize and Simplify

Water activity is different.  It’s easy to identify bad batches that could grow mold: any product over 0.7 aW can support mold growth, anything under that value will not.  It doesn’t matter which product it is.  Using water activity as a standard can eliminate the guessing over which moisture meter is correct.  As the measurement is standardized, two water activity meters measuring the same sample will give the same reading.  And if you really need to know your moisture content, a new version of AquaLab can give you both moisture content and water activity from the same measurement.

Measurements that Matter

Dried fruit and nuts do last a long time on the shelf, but not forever.  Eventually, lipid oxidation and other chemical or enzymatic reactions will make the product inedible.  Because water activity is a measure of energy, it influences how hastily these reactions can occur.