The basic process of freeze-drying
food was known to the ancient Peruvian Incas of the Andes. Freeze-drying,
or lyophilization, is the sublimation/removal of water content from frozen
food. The dehydration occurs under a vacuum, with the plant/animal product
solidly frozen during the process. Shrinkage is eliminated or minimized,
and a near-perfect preservation results. Freeze-dried food lasts longer
than other preserved food and is very light, which makes it perfect for
space travel. The Incas stored their potatoes and other food crops on the
mountain heights above Machu Picchu. The cold mountain temperatures froze
the food and the water inside slowly vaporized under the low air pressure
of the high altitudes.
During World War II, the freeze-dried
process was developed commercially when it was used to preserve blood plasma
and penicillin. Freeze-drying requires the use of a special machine called
a freeze-dryer, which has a large chamber for freezing and a vacuum pump
for removing moisture. Over 400 different types of freeze-dried foods have
been commercially produced since the 1960s. Two bad candidates for freeze-drying
are lettuce and watermelon because they have too high a water content and
freeze-dry poorly. Freeze-dried coffee is the best-known freeze-dried product.
The Freeze-Dryer Special thanks goes to Thomas
A. Jennings, PhD, author offor his reply to the question, "Who
invented the first freeze-dryer?"
"Lyophilization - Introduction and
There is no real invention of a freeze-dryer.
It appears to have evolved with time from a laboratory instrument that
was referred to by Benedict and Manning (1905) as a "chemical pump". Shackell
took the basic design of Benedict and Manning and used an electrically
driven vacuum pump instead of the displacement of the air with ethyl ether
to produce the necessary vacuum. It was Shackell who first realized that
the material had to be frozen before commencing the drying process - hence
freeze-drying. The literature does not readily reveal the person who first
called the equipment used to conduct this form of drying a "freeze-dryer".
For more information on freeze-drying or lyophilization, one is referred
to my book "Lyophilization
- Introduction and Basic Principles" or to the INSIGHTs that
appear on our web site.
Dr. Jennings' company has developed
a number of instruments that are directly applicable to the lyophilization
process, including their patented D2 and DTA thermal analysis instrument.
Trivia Freeze-dried coffee
was first produced in 1938, and lead to the development of powdered food
products. Nestle company invented freeze-dried coffee, after being asked
by Brazil to help find a solution to their coffee surpluses. Nestle's own
freeze-dried coffee product was called Nescafe, and was first introduced
in Switzerland. Tasters Choice Coffee, another very famous freeze-dried
manufactured product, derives from a patent issued to James Mercer. From
1966 to 1971, Mercer was chief development engineer for Hills Brothers
Coffee Inc. in San Francisco. During this five-year period, he was responsible
for developing a continuous freeze-drying capability for Hills Brothers,
for which he was granted 47 U.S. and foreign patents.
How Freeze-Drying Works According to Oregon
Freeze Dry - The purpose of freeze-drying is to remove a solvent (usually
water) from dissolved or dispersed solids. Freeze-drying is method for
preserving materials, which are unstable in solution. In addition, freeze-drying
can be used to separate and recover volatile substances, and to purify
materials. The fundamental process steps are:
Freezing: The product is frozen. This
provides a necessary condition for low temperature drying.
Vacuum: After freezing, the product
is placed under vacuum. This enables the frozen solvent in the product
to vaporize without passing through the liquid phase, a process known as
Heat: Heat is applied to the frozen
product to accelerate sublimation.
Condensation: Low-temperature condenser
plates remove the vaporized solvent from the vacuum chamber by converting
it back to a solid. This completes the seperation process.
of Freeze-Dried Fruits in Confectionery Products In freeze-drying, moisture sublimes
directly from the solid state to vapor, thus producing a product with controllable
moisture, no need for cooking or refrigeration, and natural flavor and
of Food in Space More than 20 years ago, astronaut
John Glenn became the first American to orbit the Earth. Among the many
tasks Glenn had to perform while in orbit were the first American space
experiments in eating food in the weightless conditions of Earth orbit.
Glenn's flight was too short to make eating a necessity, but future flights
were expected to last many days and even weeks. His experience would help
design space food systems.
JOURNAL A list of the previous issues of
INSIGHT that touch upon the lyophilization process.