467
Chapter 35
Control by Reduced
Water Activity and Drying
introduction
The ability of dried seeds, grains, tubers, and fruits to resist spoilage was probably recognized by
humans even before their discovery of agriculture. Subsequently, this simple method (drying) was
practiced to preserve the large volume of foods produced during growing seasons to make them
available during nongrowing seasons. Later, reduced A W was also extended to preserve other foods
(e.g., meat, fish, and milk) not only by removing water by drying, but also by adding solutes (e.g.,
salt, honey, and starch) to bind water.
Since the beginning, reduced A W
1 has been used throughout human civilization in many ways
not only to preserve foods and stabilize the food supply, but also to develop different types of shelfstable foods. Some of these include salted fish and meats; semidry and dry fermented sausages; dried
fish, meat, vegetables, and fruits; evaporated and sweetened condensed milk; and dry milk, cheeses,
bread and bakery products, flour, cereals, molasses, jams and jellies, chocolate, noodles, crackers, dried
potatoes, dried eggs, and confectioneries. In more recent years, new technologies have helped produce
foods with low A W by freeze-drying, puffed-drying, freeze-concentration, and osmotic-concentration
methods. In addition, a better understanding of the relationship and influence of moisture and A W on
microbial growth has been instrumental in producing many types of intermediate-moisture ready-toeat foods. Efforts are also in progress to use low A W along with other microbial control parameters, such
as low pH, vacuum packaging, and low heat, to produce ready-to-eat meat, fish, and dairy products
that can be stored at ambient temperatures for relatively long periods of time. Because of their convenience, these foods are popular; the trend shows that the popularity will continue.
objectives
The main objective of reducing A W in food is to prevent or reduce the growth of vegetative cells
and germination and outgrowth of spores of microorganisms. Prevention of toxin production by
toxigenic molds and bacteria is also an important consideration. Microbial cells (not spores) also
Chapter 35
Control by Reduced
Water Activity and Drying
introduction
The ability of dried seeds, grains, tubers, and fruits to resist spoilage was probably recognized by
humans even before their discovery of agriculture. Subsequently, this simple method (drying) was
practiced to preserve the large volume of foods produced during growing seasons to make them
available during nongrowing seasons. Later, reduced A W was also extended to preserve other foods
(e.g., meat, fish, and milk) not only by removing water by drying, but also by adding solutes (e.g.,
salt, honey, and starch) to bind water.
Since the beginning, reduced A W
1 has been used throughout human civilization in many ways
not only to preserve foods and stabilize the food supply, but also to develop different types of shelfstable foods. Some of these include salted fish and meats; semidry and dry fermented sausages; dried
fish, meat, vegetables, and fruits; evaporated and sweetened condensed milk; and dry milk, cheeses,
bread and bakery products, flour, cereals, molasses, jams and jellies, chocolate, noodles, crackers, dried
potatoes, dried eggs, and confectioneries. In more recent years, new technologies have helped produce
foods with low A W by freeze-drying, puffed-drying, freeze-concentration, and osmotic-concentration
methods. In addition, a better understanding of the relationship and influence of moisture and A W on
microbial growth has been instrumental in producing many types of intermediate-moisture ready-toeat foods. Efforts are also in progress to use low A W along with other microbial control parameters, such
as low pH, vacuum packaging, and low heat, to produce ready-to-eat meat, fish, and dairy products
that can be stored at ambient temperatures for relatively long periods of time. Because of their convenience, these foods are popular; the trend shows that the popularity will continue.
objectives
The main objective of reducing A W in food is to prevent or reduce the growth of vegetative cells
and germination and outgrowth of spores of microorganisms. Prevention of toxin production by
toxigenic molds and bacteria is also an important consideration. Microbial cells (not spores) also