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;