Dry Milk Ingredients 149of the sophisticated analytical instruments on
the market (e.g., Hosakawa micron powders
tester, Aerofl ow powder fl owability analyzer)
or simple tests involving measurement of
powder fl ow through a funnel, down an
incline, or the angle of repose after forming
a powder pile under controlled conditions.
An alternative method uses a rotating drum
developed by Niro, and this gives results for
a wide range of powders (Piesecky, 1997 ).
Measurements using this drum method indi-
cate that the fl owability of agglomerated
skim milk powder is greater than that of
agglomerated full - cream milk powder, which
is greater than that of instant full - cream milk
powder, which is greater than the fl owability
of ordinary full - cream milk powder.
Flowability is a very complex issue that is
infl uenced by many factors. It is improved by
the use of fl ow additives, minimizing the
amount of fi nes, increasing the particle size,
and having more spherical and smooth par-
ticles. An increase in moisture, particularly
surface moisture and/or fat content, particu-
larly free fat, has a detrimental effect on
fl owability.Reconsitutability
The ability of a powder to be reconstituted
depends on its ability to be wet, to sink, to
disperse, and fi nally to dissolve. Complete
dissolution is important for functionality of
powders in an application.
Wettability: In order for a powder to be
reconstituted it must fi rst be penetrated by the
water in which it is being dissolved. The
powder must be able to overcome the surface
tension between itself and the water in the
fi rst instance.
A typical method for measuring wettabil-
ity consists of systematically placing a
weighed amount of powder on the surface of
a known volume of water at a set temperature
and then measuring the time taken for all of
the powder to disappear below the surface of
the water (Pisecky, 1997 ).infl uence on other aspects of powder func-
tionality including dispersibility, wettability,
and instantizing.
The bulk density of milk powders is mea-
sured on a known weight of powder trans-
ferred to a measuring cylinder. The initial
volume is the poured bulk density. The cyl-
inder is then tapped, usually 100 times, and
then a further 525 times to give the loose
and fi nal bulk density, respectively. There are
also variations on this number of taps. There
are many manual (ADPI, 2002 ) and auto-
mated (e.g., Stampvolumeter) methods for
this determination, and the method must
always be quoted when giving determina-
tions. Typical results for skim milk powder
are in the range of 0.58 to 0.68 g/ml. For
full - cream milk powder, the bulk density
is 0.56 to 0.66 g/ml for nonagglomerated
powder and 0.45 to 0.52 g/ml for instantized
powder.
During powder manufacture many vari-
ables can play a part in the fi nal bulk density
of the powder produced including the con-
centrate characteristics, atomization method-
ology, drying parameters, and extent of whey
protein denaturation. The parameters that
determine the fi nal bulk density are the
occluded air (i.e., the amount of air entrapped
within the individual powder particles), inter-
stitial air (i.e., the amount of air or space
between the powder particles themselves),
and distribution of the size and shape of the
powder particles. Powders with a range of
particle sizes give a higher bulk density than
those with a narrow particle size distribution.
With respect to the effects of shape, powder
particles that are smoother and more uniform
give rise to higher bulk densities.
Flowability
Powder fl owability is an important attribute
of milk powders in the area of transport,
packaging, and handling. The measurement
of fl owability is particularly diffi cult.
Measurements can be carried out using one