Chemistry Reference
In-Depth Information
CHAPTER 1
Historical Background
1.1 History of Drying as a Preservation Method
The recognition that all organic matter on this planet is either water
soluble, or at least water sensitive, can be taken as a starting point of
almost everything that is discussed in this topic. Following on from this
bald statement is the unfortunate fact that aqueous solutions of many
organic substances, as well as water-sensitive solids containing even
relatively low amounts of absorbed water, tend to be subject to chem-
ical, microbial and/or physical changes, most of which are perceived to
be undesirable, perhaps even hazardous or lethal. This realisation goes
back many centuries: sailors who travelled on exploratory journeys to
faraway places learned early on to pickle their meat and other food
supplies in concentrated brine solution, so as to inhibit the growth and
proliferation of toxic principles that were known to lead to painful or
even incurable diseases.
In more modern times, refrigeration and frozen storage have super-
seded the ancient pickling processes and other, more refined methods
have been devised to render foods stable, safe and acceptable for
extended periods. Among such methods, drying takes pride of place,
insofar as it does not reduce the perceived eating quality of a product.
The advent of ''instantisation'' technology has led to a wide range of
products that bear witness to the successes achieved by controlled drying
of aqueous solutions, or of solids that contain appreciable amounts of
water. Where desirable, solid states so obtained can be readily recon-
stituted with only minor losses in eating quality. What is not universally
appreciated is that freezing as such, is in fact a drying process. As liquid
water is converted into crystalline ice from the original aqueous solution
or solid substrate, the residue becomes increasingly dehydrated. Upon
rewarming, the ice melts and, ideally, the dehydrated product can be
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