208 Chapter 9
butter is heated it displays a melting curve of
solid fat content vs. temperature that is sig-
moidal in shape, with a steep reduction in
solid fat between 10 ° C (50 ° F) and 20 ° C
(68 ° F). The addition of high amounts of veg-
etable oil results in a product with unaccept-
ably low solid fat content, showing poor
body and oiling off at room temperature
(20 ° C; 68 ° F) (Figure 9.6 ). However, dairy
spreads with higher proportions of vegetable
oil and lower solid fat contents can be pro-
duced by adopting some of the technology
and formulation aspects from the margarine
industry.
Production of spreads with good plastic
properties at refrigerator and room tempera-
tures is achieved with the use of scraped -
surface heat exchangers. A scraped - surface
heat exchanger is typically a tubular heat
exchanger cooled by a liquid refrigerant (for
example, ammonia) with scraper blades
mounted on a central shaft that rotates con-
tinuously, removing crystallized fat from the
inner tube surface to promote rapid cooling
and crystal nucleation in a short residence
time (seconds). Scraped - surface heat
exchanger units usually are employed in
combination with crystallizer units, which
hold a larger volume and have a longer resi-
dence time (several minutes). These units
work the product between a series of metal
pins fi xed within the crystallizer tube and
others mounted on a rotating central shaft,
shearing the product, preventing formation of
large crystal networks, and dispersing mois-
ture droplets. The majority of crystallization
of the fat takes place in the crystallizer unit(s)
and the blend may then be transferred to
resting tubes to continue crystallization,
although with less shear, before packing.
Most manufacturers of spreads produce a
range of products of differing fat contents
and compositions to maximize their market.
For example Dairy Crest, a major British
manufacturer of butter and spreads, includes
products within their portfolio of spreadable
fat products with fat contents that range fromaddition of a single low - melting fraction to
achieve these properties in the fi nal butter
product (Kaylegian and Lindsay 1992 ).
Dairy Spreads
It is apparent that the proportion of unsatu-
rated fatty acids must be substantially
increased to make a spreadable milk fat -
based product. This can be achieved outside
of the butter regulations by adding liquid
vegetable oil to the butter or cream to reduce
solid fat content. This is the basis of dairy
spreads and there are now a number of dif-
ferent types of dairy spreads available with
improved spreading properties and a range of
fat contents (Table 9.1 ).
The traditional dairy blend such as the
Swedish product Bregott, launched in 1976,
was prepared by injecting vegetable oil,
usually canola or rapeseed, into the cream
prior to churning in a continuous butter
maker. Because the blend of butter and oil is
softer and more spreadable at refrigeration
temperatures than butter, it is necessary to
churn the cream and oil mixture at a lower
temperature, 5 ° C (41 ° F), and maintain this
temperature throughout the process.
Obviously it is important that the vegetable
oil selected does not solidify at this tempera-
ture. The fi nal product typically has a fat
content similar to butter but with 15% to 25%
of the milk fat being replaced by vegetable
oil. Alternatively, injection of the vegetable
oil into the butter rather than the cream has
the advantage of reducing vegetable oil loss
into the buttermilk, and the high - energy - cost/
low temperature conditions for churning
cream/vegetable oil blends are not required.
Products prepared using butter (or cream)
and vegetable oils may not be labeled as
butter (Table 9.1 ).
Spreads Technology
The concentration of vegetable oil in tradi-
tional dairy spreads is limited because as