Why Freeze-Dry

The following summary gives the main responses that have been advanced by seasoned industrial managers when posed the question why freeze-dry ... 

Factors in favour of freeze-drying are undoubtedly the ability of carrying out the process under conditions of absolute sterility and the rapid reconstitution of the dried product at the point of use. It is also true that the white solid plugs, so characteristic of properly freeze-dried solutions, are widely recognised and accepted as a mark of quality by end users. The most common replies to the question Why freeze-dry are everybody else does it or this product has always been successfully freeze-dried . The widespread conservatism of company production departments is so well documented that it needs no further elaboration. 

The replies resulting from a poll of process managers in pharmaceutical companies to the question Why freeze-dry were discussed in the... 

The primary structure of the fluids that are bound to undergo freeze-drying is, of course, of great interest. In that wake, the structure of water itself is a determinant item. This is why two chapters in this book relate directly to that topic (Watts and Bellissent-Funel/Teixeira). Accordingly, we will not deal with it. However, we would like to share with our readers and colleagues some ideas that evolved from recent experiments that we have carried out on the low-temperature thermoluminescence of different systems and, in particular, on water itself. 

The dry freeze-dried cake undoubtedly has a very peculiar structure since it has been carved under vacuum from a solid matrix. At the end of this process and when it is still under vacuum, its internal surface is quite clean and very reactive. It can be easily understood that its first contact with a foreign element, such as the gas used to rupture the vacuum, is determinant. This is, in fact, why the choice of this gas as well as the procedure to introduce it are critical. In that context the properties of the dry cake internal surface constitute a major element. 

At the onset of our research work, we tried to operate in the same way with freeze-dried products that had received a strong gamma irradiation (40-60 kGy) at room temperature. The results were disappointing because we were limited to rather low temperatures (below 100°C) and, even so, when the material could stand high temperatures like freeze-dried silica. This is why we attempted to apply to these products the same methodology that we used previously for our investigation on water and solutions. 

Polymers such as dextrans could provide many desirable properties (e.g., high 7g and T ) to the freeze-dried formulation. Therefore, it is essential that future research address the theoretical and practical aspects of protein/polymer phase separation and develop the mechanistic insight to prevent this phenomenon during lyophilization. Also, as part of this effort, it is important to discern why other polymers (e.g., PVP and BSA) that protect labile proteins apparently do not phase-separate from the protein during lyophilization. 

This is why we believe that there is another solution to this problem, which we would like to propose here. According to this scheme, the whole freeze-drying operation would be carried out under clean hygenic conditions without any attempt to secure absolute sterility. Then, when the freeze-dried products are ready... 

Why is it necessary to place foods in low-pressure chambers during freeze drying ... 

This is the reason why a sustained interest is presently devoted to a new development made in the field by W. L. Gore Associates—the LYOGUARD Freeze-Dry Tray (see Picture 1). 

Coffee is an extract of a roasted bean, made with hot water. It has many components. Some companies market instant coffee, which is made by freeze-drying brewed coffee. Explain from a components perspective why instant coffee rarely has the quality of freshly brewed coffee. 

Why is the sample frozen to just below the solution eutectic rather than freezing it to a steady low temperature Commercial freeze driers use a refrigerator unit rather than dry ice acetone or dry ice isopropanol. Why is this (Hint - refer to question 4)... 

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