Question

The weight of 10 kg dried cauliflower containing 5% moisture (wet basis) after rehydration is 60 kg. If the fresh cauliflower contained 87% moisture (wet basis), calculate the coefficient of rehydration (rounded off to 2 decimal places).

Hint:

Do a dry-matter balance first to reconstruct the original fresh weight, then take the ratio \(\text{rehydrated}/\text{fresh}\) to get the coefficient of rehydration.

Answer 1

Step 1: Dry-matter balance to get original fresh weight.
Dried sample: \(W_d=10\) kg with \(M_d=5%\) moisture \(⇒\) dry matter \(=10\times(1-0.05)=9.5\) kg.
Assuming no solids loss during drying, the original fresh cauliflower had the same 9.5 kg dry matter.
Fresh moisture \(M_f=87%⇒\) dry matter fraction \(=1-0.87=0.13\).
Hence fresh weight \(W_f=\dfrac{9.5}{0.13}=73.0769\ \text{kg}\ (\approx 73.08\ \text{kg}).\) Step 2: Coefficient of rehydration.
By definition, \[ \text{Coefficient of rehydration}=\frac{\text{Weight after rehydration}}{\text{Original fresh weight}} =\frac{60}{73.0769}=0.8217\approx \boxed{0.82}. \]