Snapshot 1: hygroscopic food powder exposed to moderately moist air

Snapshot 2: grain exposed to moist air

Snapshot 3: dried legumes soaked in water

Dry foods can absorb moisture by exposure to a moist atmosphere or by soaking in water. The curve depicting the moisture gain versus time can frequently be described by the empirical model based on the formula

, where

is the moisture content (on a dry or wet basis) at time

,

and

are the initial and equilibrium moisture contents, respectively, and

is a characteristic time constant. This Demonstration generates dynamic water absorption curves using this model. It also generates curves depicting the relationship between the fraction of the equilibrium,

, and the time needed to reach it,

.

The corresponding plot shows either the moisture versus time relationship or the time versus fraction of equilibrium for the entered parameters. Note that the latter does not always start at

but at

. Its numerical value is displayed above the plot. Also shown is the numerical value of

, the momentary fraction of equilibrium reached at time

. The slider-entered

or

values and the corresponding

or

values are shown as moving dots on the curves and their numerical values are also displayed above the plot.

The model can probably also be used for nonfood hygroscopic materials and liquid-absorbing dry gels. Not all possible plotted curves correspond to real physical systems.

M. Peleg, "An Empirical Model for the Description of Moisture Sorption Curves,"

*Journal of Food Science*,

**53**, 1988 pp. 1216–1217 and 1219.