found a good article on freeze drying.
What is Freeze-Drying?
Freeze-drying is a simple process that removes water (moisture) from frozen products, documents or keepsakes while they remain in a frozen state, thereby maintaining shape and biological structure.
How Does Freeze-Drying Work?
There are four basic requirements to freeze-dry a product.
The object to be freeze-dried must be frozen solid. This freezing will lock the product structure firmly into position. The object is positioned before freezing to the shape you want at completion. It is important to note that the product must be frozen solid or it will not freeze-dry.
A condensing surface must be provided which is colder than the product to be dried. This surface is typically colder than -40¬į Centigrade. This condensing surface helps attract the vapor from the product being dried; it also protects the high-grade vacuum pump from water, oils and fats that come from the product being freeze-dried.
A vacuum pump that will provide a very low absolute pressure must be provided. A vacuum is a space void of air with NO leaks. During freeze-drying, you actually mechanically create vacuum/negative atmosphere lower than the pressure of outer space. These extremely low pressures are required to complete the freeze drying process.
To freeze-dry successfully you need a heat source. This can be provided in many ways such as heat coils, lights, etc. By providing heat, you promote the release of bound water from the product. Bound water is the hardest to get out of the product.
What Actually Happens?
The frozen product is placed in a chamber. The chamber contains or is connected to a condenser. A vacuum pump is connected in series to the chamber and the condenser. The vacuum pump is turned on. When the inside of the chamber reaches the proper pressure, a vapor of moisture leaves the frozen product and collects on the condenser. This process is called sublimation. Sublimation by definition is the process in which a solid (ice) is transferred from a solid state directly to a gaseous state, and then recollected as a solid, without melting or returning to a liquid state. After time, heat is slowly applied to the product, which will help drive off more vapors and eliminate bound water.
What Can Be Freeze-dried?
Freeze-drying is ideal for the recovery of water-damaged documents, books, artwork, keepsakes, and the preservation of whole animals, floral products, food and drugs. Freeze-drying has been used worldwide in schools, museums, laboratories, food manufacturing, nature interpretative centers, taxidermy studios, and many other applications. You may be drinking freeze-dried coffee right now, and most of the food used by NASA in our space programs has been freeze-dried. You may have an idea about preserving something with a freeze-dryer that could turn out to be a fantastic business opportunity just waiting for you to develop it.