134 Chapter 5
the precautions listed for the sediment test
above, it is important that the coffee be
freshly made because the color of coffee
darkens on standing.Membrane Concentration
Technologies
The application of membranes to concentrate
milk has become increasingly important in
the dairy industry. Unlike evaporation, it is
a technique used to concentrate milk with
little or no heat treatment. The milk compo-
nents are separated based on their molecular
mass and shape under pressure using spe-
cially designed semi - permeable membranes.
The different membrane processes used in
the dairy industry are microfi ltration (MF),
ultrafi ltration (UF), nanofi ltration (NF), and
reverse osmosis (RO). During concentra-
tion by membrane processes, the portion of
the liquid that passes through the membrane
is called permeate, and the concentrated
liquid retained by the membrane is called
retentate.
The word membrane, derived from Latin,
means skin. Membrane technologies have
been used in the dairy industry for more than
30 years (Grandison and Clover, 1997 ). UF
and RO systems were fi rst reported to be
used in the dairy industry in 1975 (Bargeman
et al., 2005 ). NF was commercially intro-
duced in the dairy industry around 1984 to
simultaneously concentrate and demineralize
whey; it is a process between UF and RO.
MF is a low - pressure membrane separa-
tion process using membranes of fairly large
pore size and small pressure differential,
thereby allowing particles greater than 0.1 μ m
(0.05 to 10 μ m) to pass through. Thus, it is
used to remove small suspended particles and
microorganisms from milk.
UF is a selective fractionation/concentra-
tion process using pressures up to 145 psi
(10 bar) to separate macromolecules and
suspended solids with molecular weightream layer may not be noticeable in well -
homogenized milk before the products is 2
months of age.
Sedimentation
Sedimentation is a subjective visual test. It
is the sediment observed at the bottom of
a package after pouring out the product com-
pared to an internal standard chart developed
with different degrees of sediments. Alter-
nately, sedimentation is calculated as the
weight difference of the container before and
after rinsing off sediment.
Viscosity
The viscosity of concentrated milk is higher
than that of normal milk and is in the range
15 to 60 mPa.s (cP). It is affected by fat and
protein contents of milk and processing con-
ditions such as heat treatment. Typically the
test is done using a Brookfi eld viscometer
equipped with spindle number 2 at 60 rpm.
The temperature of the concentrate is kept at
40 ° C (105 ° F) ± 0.5 ° C.
Coffee Sediment
In the coffee sediment test, the addition of
evaporated milk to hot coffee is simulated
and the quantity of sediment formed after
centrifugation is measured. The results of the
test are infl uenced by the composition of
coffee, pH, temperature, and quantity of
water used to make the coffee. Therefore, it
is important to standardize the method,
including the type and brand of coffee used,
to obtain reliable results.
Coffee Whitening
The coffee whitening test is similar to the
coffee sediment test but instead of centrifug-
ing out the sediment, the color is measured
using a refl ectance colorimeter. In addition to