Foam

A presentation about foam in aerated food such as ice cream, whipped cream, marshmallow, etc.

1. 1"
FOAMS!
Photo"courtesy"of"Dan"Phiffer"on"Flickr"
Photo"courtesy"of"Leslie"on"Flickr"
Photo"courtesy"of"Alpha"on"Flickr"
Prof. Abd Karim Alias
Universiti Sains Malaysia
This"work"is"licensed"under"a"Crea=ve"Commons""
A@ribu=onBNonCommercialBShareAlike"3.0"Unported"License."

2. 2"
! Foam is a two-phase system in which the
gas (air) phase is dispersed in a small
amount of liquid (water) continuous
phase.
! Foam is desirable in beer; it is also
promoted in whipped egg white (e.g., for
making cakes, meringue, etc.), ice cream,
marshmallow, etc.
FOAM:
DEFINITION & CHARACTERISTICS
Abd Karim Alias, 2013

3. 3"
! A bubbly foam (e.g. in ice cream) is formed
when the amount of gas incorporated is low
enough for bubbles to retain roughly
spherical shape.
! Polyhedral foam (e.g., beer foam) – the gas-
to-liquid ratio is so large that bubbles are
pressed against one another in a honeycomb-
type structure.
FOAM STRUCTURE
Abd Karim Alias, 2013

4. 4"
FOAM STRUCTURE
Abd Karim Alias, 2013

5. 5"
FOAM STRUCTURE
Abd Karim Alias, 2013

6. 6"
! Three process steps for foam formation:
! air has to be injected into the liquid (e.g.
using a mixer)
! large air bubbles have to be broken up
into smaller bubbles
! the smaller bubbles have to be prevented
from fusing during the formation of a
foam
FOAM FORMATION
Abd Karim Alias, 2013

7. 7"
! A surface active foaming agent is
essential for the formation of stable foam
! The foaming agent lowers the surface
tension of the liquid phase & allows
expansion of its surface area.
! The surfactant forms a closely packed
film around the dispersed gas bubbles.
FOAM FORMATION –The role of surface
active agent
Abd Karim Alias, 2013

8. 8"
Three processes involved in the stabilization
of protein foams:
! adsorption of the protein at the gas-
liquid interface,
!  surface denaturation,
! coagulation of protein.
FOAM FORMATION –Proteins as surface
active agent
Abd Karim Alias, 2013

9. 9"
FOAM FORMATION –Proteins as surface
active agent
Abd Karim Alias, 2013

10. 10"
Three factors affecting foam stability:
! drainage: the draining of liquid from
foam
! disproportionation: the change in foam
bubble size distribution caused by gas
diffusion from small to large bubbles
! coalescence: the fusion of foam bubbles
FOAM STABILITY
Abd Karim Alias, 2013

11. 11"
• Water drains from
foam under gravity
• A foam drains along
lamellae to the
curved junction of
thin lamellae
(plateau borders),
where the pressure
is lower.
FOAM STABILITY : FOAM DRAINAGE
Abd Karim Alias, 2013

12. 12"
FOAM STABILITY : FOAM DRAINAGE
• As water leaves,
faces of film are
brought closer
together
Click picture to view animation
Abd Karim Alias, 2013

13. 13"
• The diffusion of gas from small bubbles
into big bubbles is referred to as
disproportionation.
• In the absence of a stabilizing film of
polymer molecules, disproportionation
occurs remarkably quickly.
• Probably the most important type of
instability in foams.
FOAM STABILITY : Disproportionation
Abd Karim Alias, 2013

14. 14"
! Egg foams (egg white) are essential in the
preparation of angel cakes, sponge cakes,
meringues, souffles, etc.
! The proteins not only lower the surface
tension of egg white but some are denatured
at the surface.
! The coagulation of proteins at the gas-liquid
interface form a network that gives some
rigidity & stability to the foam.
EGG FOAMS
Abd Karim Alias, 2013

15. 15"
EGG FOAMS
Abd Karim Alias, 2013

16. 16"
! Globulins appeared to be good foamers,
producing small gas bubbles & a large
volume.
! Ovomucin is not a good foamer by itself but
stabilised the foam because it is rapidly
insolubilised (denatured) at the bubble
surface.
! The presence of fat, even in small amounts,
and egg yolk, have a detrimental effect on
foam formation.
EGG FOAMS
Abd Karim Alias, 2013

17. 17"
! The presence of lipids retards foaming because
the oil molecules migrate to the air-water
interface before the protein molecules, inhibiting
the unfolding of the protein & thus the
formation of foam.
! The antifoaming behavior of egg yolk is partly
due to the presence of lecithin, which is believed
to bind to egg white proteins, preventing them
from associating at the air-water interface, &
competitively displacing them from the
interface.
EGG FOAMS
Abd Karim Alias, 2013

18. 18"
! Increase of [protein] increases both the
foamability & foam stability, mainly because
of viscosity effect which produces a thicker
lamella film.
! Adjusting egg white pH to 6.5 by adding an
acid ingredient increases foam stability to
heat, because the acid makes foam less
prone to over-coagulation.
! Sugars enhance foam stability by increasing
the viscosity of lamellar fluid which reduces
the drainage rate.
EGG FOAMS
Abd Karim Alias, 2013

19. 19"
! In fact, foams can cause many problems,
including vessels overflowing, processing and
packaging interference, damaging materials
and housekeeping issues
! Silicon dioxide is the most common chemical
used in defoamers and antifoams, as it can
destroy and suppress processing foams.
FOAMS ARE NOT ALWAYS DESIRABLE!
Abd Karim Alias, 2013

20. 20"
Knowing when to produce foam and when to
get rid of it are one of the many keys to
product success!
Abd Karim Alias, 2013