Freeze-drying

The invention: 

Method for preserving foods and other organic matter by freezing them and using a vacuum to remove their water content without damaging their solid matter.

The people behind the invention:

Earl W. Flosdorf (1904- ), an American physician
Ronald I. N. Greaves (1908- ), an English pathologist
Jacques Arsène d’Arsonval (1851-1940), a French physicist



Freeze-Drying for Preservation 

Drying, or desiccation, is known to preserve biomaterials, including
foods. In freeze-drying, water is evaporated in a frozen
state in a vacuum, by means of sublimation (the process of changing
a solid to a vapor without first changing it to a liquid).
In 1811, John Leslie had first caused freezing by means of the
evaporation and sublimation of ice. In 1813, William Wollaston
demonstrated this process to the Royal Society of London. It does
not seem to have occurred to either Leslie orWollaston to use sublimation
for drying. That distinction goes to Richard Altmann, a
German histologist, who dried pieces of frozen tissue in 1890.
Later, in 1903, Vansteenberghe freeze-dried the rabies virus. In
1906, Jacques Arsène d’Arsonval removed water at a low temperature
for distillation.
Since water removal is the essence of drying, d’Arsonval is often
credited with the discovery of freeze-drying, but the first clearly recorded
use of sublimation for preservation was by Leon Shackell in
1909. His work was widely recognized, and he freeze-dried a variety
of biological materials. The first patent for freeze-drying was issued
to Henri Tival, a French inventor, in 1927. In 1934, William
Elser received patents for a modern freeze-drying apparatus that
supplied heat for sublimation.
In 1933, Earl W. Flosdorf had freeze-dried human blood serum
and plasma for clinical use. The subsequent efforts of Flosdorf led to
commercial freeze-drying applications in the United States.

Freeze-Drying of Foods

With the freeze-drying technique fairly well established for biological
products, it was a natural extension for Flosdorf to apply the
technique to the drying of foods. As early as 1935, Flosdorf experimented
with the freeze-drying of fruit juices and milk. An early British
patent was issued to Franklin Kidd, a British inventor, in 1941 for
the freeze-drying of foods. An experimental program on the freezedrying
of food was also initiated at the Low Temperature Research
Station at Cambridge University in England, but untilWorldWar II,
freeze-drying was only an occasionally used scientific tool.
It was the desiccation of blood plasma from the frozen state, performed
by the American Red Cross for the U.S. armed forces, that
provided the first spectacular, extensive use of freeze-drying. This
work demonstrated the vast potential of freeze-drying for commercial
applications. In 1949, Flosdorf published the first book on
freeze-drying, which laid the foundation for freeze-drying of foods
and remains one of the most important contributions to large-scale
operations in the field. In the book, Flosdorf described the freezedrying
of fruit juices, milk, meats, oysters, clams, fish fillets, coffee
and tea extracts, fruits, vegetables, and other products. Flosdorf also
devoted an entire chapter to describing the equipment used for both
batch and continuous processing, and he discussed cost analysis.
The holder of more than fifteen patents covering various aspects of
freeze-drying, Flosdorf dominated the move toward commercialization
in the United States.
Simultaneously, researchers in England were developing freezedrying
applications under the leadership of Ronald I. N. Greaves.
The food crisis duringWorldWar II had led to the recognition that
dried foods cut the costs of transporting, storing, and packaging
foods in times of emergency. Thus, in 1951, the British Ministry of
Food Research was established at Aberdeen, Scotland. Scientists at
Aberdeen developed a vacuum contact plate freeze-dryer that improved
product quality and reduced the time required for rehydration
(replacement of the water removed in the freeze-drying
process so that the food can be used).
In 1954, trials of initial freeze-drying, followed by the ordinary
process of vacuum drying, were carried out. The abundance of
membranes within plant and animal tissues was a major obstacle to
the movement of water vapor, thus limiting the drying rate. In 1956,
two Canadian scientists developed a new method of improving the
freeze-drying rate for steaks by impaling the steaks on spiked heater
plates. This idea was adapted in 1957 by interposing sheets of expanded
metal, instead of spikes, between the drying surfaces of the
frozen food and the heating platens. Because of the substantially
higher freeze-drying rates that it achieved, the process was called
“accelerated freeze-drying.”
In 1960, Greaves described an ingenious method of freeze-drying
liquids. It involved continuously scraping the dry layer during its
formation. This led to a continuous process for freeze-drying liquids.
During the remainder of the 1960’s, freeze-drying applications
proliferated with the advent of several techniques for controlling
and improving the effectiveness of the freeze-drying process.

Impact

Flosdorf’s vision and ingenuity in applying freeze-drying to
foods has revolutionized food preservation. He was also responsible
for making a laboratory technique a tremendous commercial
success.
Freeze-drying is important because it stops the growth of microorganisms,
inhibits deleterious chemical reactions, and facilitates
distribution and storage. Freeze-dried foods are easily prepared for
consumption by adding water (rehydration). When freeze-dried
properly, most foods, either raw or cooked, can be rehydrated
quickly to yield products that are equal in quality to their frozen
counterparts. Freeze-dried products retain most of their nutritive
qualities and have a long storage life, even at room temperature.
Freeze-drying is not, however, without disadvantages. The major
disadvantage is the high cost of processing. Thus, to this day, the
great potential of freeze-drying has not been fully realized. The drying
of cell-free materials, such as coffee and tea extracts, has been extremely
successful, but the obstacles imposed by the cell membranes
in foods such as fruits, vegetables, and meats have limited
the application to expensive specialty items such as freeze-dried
soups and to foods for armies, campers, and astronauts. Future eco-
nomic changes may create a situation in which the high cost of
freeze-drying is more than offset by the cost of transportation and
storage.


See also :  Electric refrigerator; Food freezing; Polystyrene;