Two Letters Re: Harvest Right Freeze Dryer


Thanks for the review of the freeze dryer, I’m very interested. Just wanted to share that the first thing I thought when reading your review and clicking on their pictures is “that display is going to go bad”! And it did. Gotta worry about $4K and something major (and predictable) goes like that, with only a 1 yr warranty. – M.R.

HJL Replies: I was initially worried about that, too, but the company was very responsive in taking care of the issue. While I did the repair myself, they offered to have a local appliance repairman do the work. i felt comfortable enough with the simplicity of the machine to repair it myself. I think they’ve done an admirable job of keeping the cost down by using off-the-shelf parts as much as possible. Even the display that went bad was off-the-shelf. It had a part number written on it that I used to find a replacement on the Web for only $23. One of the questions that always worries me when dealing with a small business is “Will they still be in business in ten years?” I think this company will be around due to how they handle business. If not, if your google-fu has any strength to it, you should be able to find everything but the main processing board, vacuum chamber, and casing on the web.

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In the product review of the Harvest Right freeze dryer part 2, the author had his butter make a total mess of the unit. If the author was either an astronaut or scuba diver, he would understand his problem. The problem is nitrogen!

In a freeze dryer, we are dealing with both pressure and temperature. The pressure is why the butter exploded in the freeze dryer. Butter is a lipid (fat) and likes to store nitrogen. This is part of the reason why the butter exploded. It is also part of the reason why a diver or astronaut will get the “bends” or decompression sickness. Also, butter is somewhat of a whipped product, and therefore contains trapped air as well. It was when the pressure was reduced to the point that the trapped gasses overcame the adhesion strength of the butter, and the butter began to melt and expand all over the dryer unit.

With a diver, he has to breathe air at ambient pressure just to breathe at all. As he descends, the ambient pressure increases, so the air he breathes must be supplied at higher and higher pressure. This drives gas into solution in his blood at higher pressures than at the surface. The diver has only so much time at these higher pressures before he becomes too saturated to safely return to the surface. If he becomes too saturated he must first decompress at a shallower depth before he can return to the surface, or the gasses will come out of solution in his tissues or blood. The body can withstand a pressure difference of about 2 atmospheres before the gas comes out of solution. An astronaut going on a spacewalk faces the same problems, as he’s going from a high pressure to a lower pressure. Currently, astronauts must “breathe down” for six hours before being exposed to space. This is the same decompression that a diver must do.

Lipids or fats have an affinity for nitrogen and like to hold on to it. Because of this, it may take more time than normal to fully decompress. Overweight divers are much more likely to get bent than thin divers. Since butter is a fat, it will hang on to a lot of nitrogen and not give it up easily. So the butter needs to be decompressed for at least 6-12 hours at about 368 torr or 14.5 inches of mercury, and then again for 6 – 12 hours at 184 torr or 7.25 inches before going to full vacuum. This staged decompression would be a rough guess as to what is needed, and another stop at 90 torr wouldn’t be a bad idea. 1 torr = 1 mm of mercury. 1 inch of mercury = 25.4 torr – H.W.

HJL Replies: Sadly, we have to work within the boundaries of the unit. The capabilities that you speak about are only available on laboratory-grade freeze driers with very high price tags. For this unit, the vacuum is either on or off. The heating element is also either on or off. While it would be nice to have such capabilities, I would rather have the simpler unit at the less expensive price. There are other ways of taking care of butter and fatty foods that don’t involve tremendous investments in machinery. I do appreciate your scientific explanation.