Foams can be defined as a colloidal dispersion in which gas is the dispersed phase and the liquid is the continuous phase . topics included in this slide Foams, Foam formation, Foam stability, Factors affecting foam stability , Factors promoting Foam stability.

1. FOAMS

2. TOPICS
 FOAMS
 FOAM FORMATION
 FOAM STABILITY
 FACTORS AFFECTING FOAM STABILITY
 FACTORS PROMOTING FOAM STABILITY

3. FOAMS
• Foams can be defined as a colloidal dispersion in which gas is the
dispersed phase and liquid is the continuous phase.
• The dispersion medium is usually a liquid that is sometimes modified
into a solid by heating or strengthened by a solid.

4. STRUCTURE OFA FOAM

5. FOAM FORMATION
 If we produce a foam, energy must be supplied (by whipping)
to incorporate gas into the liquid, to breakup large bubbles in to
smaller ones, and to spread the liquid phase around the gas bubbles
as they form.
 The foaming agents, which is contained in the liquid phase, absorbs
at the surface of the liquid , reducing surface tension and also
forming a film around the gas bubbles.
 If the surface tension is low, the liquid will spread rapidly around
the gas bubbles during whipping.
 If newly formed gas bubbles are not immediately coated with
forming agent; they will burst or coalesce and be lost.

6. FOAM STABILITY
 The stability of a foam may be measured in terms of loss of foam
volume over a period of time.
 When a liquid is whipped to a form a foam, the volume of the liquid
increases due to incorporation of air.
 If the foam is stable, the volume does not change very much.
 However, loss of air from an unstable foam may cause a considerable
reduction in volume.

7. FACTORS AFFECTING FOAM
STABILITY
 Drainage of the liquid film between gas bubbles.
 Rupture of the interfacial tension around gas bubbles film.
 Diffusion of gas from small to large bubbles.
 Evaporation of the continuous phase.

8. FACTORS PROMOTING FOAM
STABILITY
o Stable viscoelastic surface film.
o Very viscous continuous phase.
o Low vapour pressure liquid.

9. REFERENCES
 Dr. N Shakuntala manay and M . Shadaksharswamy. Food – Facts
and principles 2nd edition page no- 149.
 A Gocl . Colloidal chemistry . Discovery publishing house page no-
151-155.
 Vaclavik V and Christian E.W . Essentials of food science, 3rd
edition , page no-322-326

10. ARUN KUMAR A
MSC FOOD SCIENCE & NUTRITION
PERIYAR UNIVERSITY, SALEM