Capacitance question?

Question

The freshness of fish can be measured by placing fish between the plates of a capacitor and measuring the capacitance. How does this work?

Answer 1

When fish is placed within the plates of capacitor (having known dielectic medium (say air) then upon deterioration the most significant, and earliest changing, parameter is the loss of water due to evaporation.

As water entails the highest dielectric constant, amongst all liquids+gases - being ideal to minutest relative changes, there is a prominent overlapping of dielectric constant gradient from the boundaries of fish surface isotropically.

Water, being dipolar, is easily affected by electric field within capacitor. In such a variable state, if capacitor is made to (used) observe the shape of relected pulse from the surface boundary of fish then the changing capacitance would give visual effect of deteriorating fish with time.

One can estimate the degree to which deteriration has taken place by observing pulse pattern in-turn induced by change in Capacitance owing to dielectric constant variation.

Answer 2

The di-electric properties of fish, after death, decrease at a known rate. I dont know how they came up with the rate, but it is known. Given this, a measure of freshness could be extrapolated from a measurement of the fishs di-electric strength, or by measuring its capacitance.