ABSTRACT
Blanching is carried out as a pretreatment for freezing,
canning, and drying. In 2003, 9.8 and 13.8 million metric
tons of vegetables for freezing and canning, respectively,
were produced in the United States with a total farmgate
value of $1.4 billion. Studies on the effects of blanching as
a pretreatment for freezing date back to the late 1920s and
early 1930s, and have been reviewed.[1] Most vegetables
are blanched prior to freezing to inactivate enzymes that
cause the development of off-flavors and off-colors during
frozen storage. Some exceptions include onions, leeks, and
peppers because they lose flavor and color on blanching.
Blanching removes trapped air (e.g., in broccoli florets)
and metabolic gases within vegetable cells and replaces
them with water, forming a semicontinuous water phase
that favors a more uniform crystal growth during freezing.
Gas removal is the main benefit of blanching before can-
ning because it allows easier can fill, reduces strain on can
during heating, and reduces can corrosion. Although, in
this case, enzyme inactivation also takes place, it is not
relevant because any remaining activity is destroyed on
retorting.[2] Blanching facilitates peeling and dicing, and is
also accompanied by microbial load reduction. Fruits are
usually not blanched, or blanched under mild (low tem-
perature) conditions prior to freezing because blanching
produces undesirable texture changes. Before drying, fruits
and vegetables are sometimes blanched.[3] After blanch-
ing, vegetables are quickly chilled by spraying with cold
water, or by conveying them to a flume of cold water that
often serves to transport them to the next part of the
process. Blowing cold dry air has also been used to take
advantage of evaporative cooling, using the water adhered
to the surface of the product.
