Kadam, Patil, Kaushik - Foam Mat Dryingdried powder certain physical properties, especially during reconstitution, which are
detrimental to its commercial appeal. For example, upon reconstitution of juices from
monoglyceride type powders a very white, milky, unnatural appearance often results.
This is due to dispersion of microscopic bubbles of gas distributed throughout the solu-
tion. The monoglyceride acts as a very effective emulsification agent forming a tho-
roughly dispersed "air sol." This effect has been reduced by the use of a "warm-rolling”,
technique which increases the bulk density of the powder. This technique was not com-
pletely effective in eliminating the unnatural appearance, however, and has the added
disadvantage that it impedes solubility. Another undesirable effect in solution of monog-
lyceride powders is the formation of a layer or "head" of foam after the juice has been
reconstituted. In solutions which do not exhibit the milky initial appearance there are
often sufficient small bubbles dispersed throughout the solution that 15 minutes or
more after reconstitution a layer of light colored material accumulates at the top and the
solution becomes unsightly. This effect occurs in almost all solutions made from powd-
ers using glyceride-ester type foaming agents. Although the densification procedure im-
proves the initial appearance, it does not have much effect on diminishing this "layer" of
foam.
5.4.1. Foam Expansion
Foam Expansion (%) = V 1 - V 0 X 100
V 0
Where V 1 is Final volume of foamed product in cm^3
And V 0 is the initial volume of the product in cm^35.4.2. Foam Stability
Foam stability is determined by measuring the reduction in foam volume at definite
intervals of time by using the following relationship
Foam stability = V 0 Δt
ΔV
Where ΔV is the change in volume of foam occurred during the time interval.5.4.3. Foam density
The density of the foamed material (Juice/ pulp) can be determined in terms of mass
by volume and represented as g/cm^3.
Foam density = ρ V 0
V 1
Where, ρ is the density of the material (Juice/ pulp)5.5. DRYING OF FOAMS
In order to dehydrate the foams, different drying techniques like vacuum foam dry-
ing, foam spray drying, foam-mat drying including crater techniques are in practice
worldwide. Development of a belt-type foam-mat dryer and production of free flowing,
rehydratable powders from tomato juice, milk, coffee extract orange juice, pineapple