I need to measure the water activity in some prunes. Can you steer me in the right direction? (A.L.)
See the following site for a water activity meter that might work for you. <http://www.aqualab.com/products/water-activity-meters/pawkit/>. They do not list the price but as I remember it is several hundred dollars.
The other option is to buy a relative humidity meter that has a probe you can insert into the lid of a jar. Put the prunes in the jar, close the lid, and insert the humidity sensor. The relative humidity (RH) should be fairly constant in a few minutes. Divide the RH reading by 100 and you have water activity (Aw). One caution, all electronic RH meters need to be checked for calibration. A calibration kit costs about $50 or so.