I spent quite a bit of time, over the last three years, researching how freeze drying is accomplished. I wanted to know why and how it worked and ultimately, if I could do it at home. Earlier, I alluded to some pretty bad information I had run across, and I think a short primer of what makes freeze drying successful is in order, so that the user can understand just how useful this appliance actually is.
It is well understood by any high school student who has taken a physics or physical science course that there are three basic forms that matter can take– solid, liquid, and gas. (Yes, I know. Plasma counts there too, but we aren’t going to talk about it.) We can force matter into any of those states by varying the temperature or pressure. Usually, we do so by varying the temperature. You do this every time you put water in your freezer to make ice. We happen to know that water turns to a gas at 212 degrees Fahrenheit (boiling) and turns to a solid at 32 degrees Fahrenheit (ice). A little lesser known but just as important is that those numbers change as the pressure changes. If you are a mountain climber, the water boils at roughly 193 degrees Fahrenheit (F) when you are at 10,000 feet elevation. For the survivor, this change can be critical, as the lowered boiling point means you may not be killing all the bad stuff in your water that you are trying to purify, but that’s another story for another time.
There is one more property of water that we need to know about in order to take advantage of it. Water can exist in all three states at the same time, within a certain temperature range. At 32 degree F, you can have some of the water as liquid, some of it as a solid, and some of it will actually be water vapor (gas). We are all familiar with the concept of ice thawing into water on the ground during a spring thaw, and if the sun is gently warming the air, you can actually see the water turning to vapor or mist. What you may not be aware of is that not all of the water goes through that cycle. Some of it turns directly from the solid ice into water vapor in a process we call sublimation. This is the process that we want to enhance to create a freeze dryer. When we freeze a cellular-based object, like food, we damage the cells because the water expands as it freezes, thus bursting the cell walls. When it begins to thaw out, it usually turns into a sloppy mess, just like a spring thaw. If you are cooking the food as that process happens, you usually don’t notice the texture change, because your cooking will do much the same damage to the cellular structure. However, the loss of integrity of those cellular walls means that the object will degrade much quicker than normal. If you’ve ever found lettuce in your refrigerator crisper that has now turned slimy and dark while parts of it are still crisp and green, you’ve probably seen this kind of behavior.
This is why when we loose power to our freezers, we generally loose all of the food contained in them. Once the cellular damage has occurred and the thawing has started, you can’t repair it. If you catch it in time, you can stop further degradation, but you can’t reverse it. However, what if you could keep the cellular structure intact despite the thawing? By removing all of the water from the food without letting it thaw, we essentially “stop” any degradation of the product when it warms up. You are also generally capable of keeping the vitamins intact, though you still need to protect them from oxidation– the interaction with oxygen that destroys flavor and vitamins and makes oils go rancid. An added benefit of freeze drying is that bacteria can’t really survive in a perfectly dry environment, so we essentially stop the bacterial action that would normally occur outside of freezing temperatures and cause your food to rot. There are a few draw backs to be sure. Without the full cellular integrity and the water to fill the cells, the food becomes brittle and easily broken into pieces. You also need to replace all of the water for your body to be able to utilize it as an energy source. If you are not re-hydrating the food before you eat it, you will need to re-hydrate your body, as the food will simply steal the water from you. Both dehydrators and freeze dryers remove the water, but the difference is that if the water is removed in a liquid state, the cell walls collapse, shrinking the food and making it take longer to re-hydrate it. Freeze drying, on the other hand, freezes the food and then removes the water keeping the cellular structure from collapsing, despite its damaged state. It is also tremendously easier to re-hydrate the freeze dried food because the water can easily penetrate the entire structure.
The concept is very easy. Once you figure out that you can manipulate that temperature/pressure boundary, you simply have to create the right “atmosphere”, or lack thereof, to encourage the process. The very small pressures involved in manipulating that boundary requires some special tools and measurement abilities. Most people in the prepping community have heard of the Tilia FoodSaver. It’s a very useful vacuum sealing machine that will produce about 29 inches of mercury (Hg). At 29 inches of Hg, we can make water boil at about 75F, but that is still above the freezing point and where we don’t want it. The water can exist as a liquid there, which defeats the whole purpose. Don’t even try that route. What you need is a vacuum pump that uses rotating vanes or gears in an oil bath to create a really good vacuum. We need to be able to make water boil at well below freezing in order to accomplish what we want. The pump supplied with the Harvest Right can reach vacuum levels that we can no longer effectively read in inches of mercury, so we have to switch to a smaller scale, which we will call millitorr (mTorr or 1/25400 of an inch). At one Torr (1000 mTorr), water will boil at about 3 degrees F, making it perfect.
In our freeze dryer, we can freeze the food to roughly -30F. We can then turn on the vacuum pump and reduce the pressure to below 1000mTorr. Then all we have to do is gently warm the food until it begins to reach the temperature at which the ice will sublimate into gas without ever turning to liquid. If the gas starts to overwhelm our vacuum pump, we simply turn the heaters off and allow the system to cool back down until the water ceases to sublimate. Then we start the cycle again. That’s it. In a nutshell, we have just described how the system works.
We still have to do something with that water vapor tough, because if we let it get pulled through the pump oil, some of it gets trapped in the oil and the oil becomes less effective. Eventually, enough of it gets into the oil that the system can no longer pull a low enough vacuum and we have to stop and change or clean the oil to continue. Harvest Right’s solution is simply to keep the freezer part running through the whole process. As the water sublimates out of the food, the vapor eventually comes in contact with the wall of the vessel, which is near -30F. Since water vapor would take less than 150mTorr to exist, it simply refreezes on the wall of the vessel, which you allow to defrost once you are through with the batch. It is an elegantly simple process that is capable of running itself with very little intervention, if any at all.
Those who have run dehydrators for your food preps usually understand that bananas and chives are not really two things that you want to run in the same batch. The chives, while yummy, are especially odoriferous and nobody likes chive-flavored bananas. Do it once in a dehydrator, and you’ll probably never do it again. We started the bananas at 0900, and I let the cooling process run for four hours. I knew I was pushing it, but most users of this machine will end up pushing the times sooner or later, so I figured we would simply use this as a learning experience. In essence, I expected some failures. At the four hour mark, I opened the freezer and felt the bananas. They were cold and hard, so I decided to push the process on. The top knob on the right side controls the timer for the cooling process, the bottom knob controls the timer for the drying process. I rotated the top knob until the cooling timer reached zero. The vacuum pump sprang to life, and the door began to compress against the chamber seal. I carefully watched the door, knowing that there was nearly 1,800 pounds of pressure there. The door snugged against the chamber, showing about a 1/2 wide contact ring with the seal. If you step away from the machine and eyeball it, you can see a slight bow to the door, but it’s obvious the system is built to take the pressures involved. I had expected the system to immediately start the drying timer, but it did not. The vacuum pump ran until the pressure reached 480 mTorr. Then the heaters kicked in, and the drying timer started. I watched the pressure begin to climb. When it reached 580 mTorr, the heaters turned off, and the timer disappeared until the pressure had dropped again to 480 mTorr. This cycle continued for about 10 hours. Finally, the timer came on and stayed on. As the pressure began to drop, I unilaterally decided that the time was up after the timer had run two hours (leaving four on the clock), and I shut the machine down. When I opened it up, the chives were done, and the bananas looked good but were still cold in the middle. There was no hint of chive flavor on the bananas either. I put the bananas back in the machine, forced it into the drying mode, and let the timer run out. Qualified as a partial success, my fiddling with the timers was obviously the problem. On thicker foods, you must let the timer run the full six hours (or longer, depending on the food).
Over the course of a month, I ran the Harvest Right Freeze Dryer 24/7, with a variety of foods. I played around with the timer settings, attempting to get better performance than just the standard programming, but it was hard to do. The standard program is a great place to start and stay. Where you will find some leeway is in how you prepare the foods for the freeze dryer. If you pre-freeze foods, you can cut the cooling time down by several hours. If you keep the prepared foods to less than 1/2” thick with no skins and good surface contact on the trays, you can cut the drying timer down to three or four hours. If you just want to come home from the grocery store and put freshly prepared foods in the freeze dryer, leave the standard controls where they are.
Several times we ran liquids through the machine, such as milk and scrambled eggs, and our first attempt involved pre-freezing the liquids in ice cube trays. The unit comes with only four trays, and to keep it running efficiently, you really need to prepare foods and pre-freeze them. Good luck finding quality ice-cube trays though. Some liquids, such as milk, contain sugar and create a sticky hard cube that just doesn’t want to release from the tray. I broke six trays before I found that I could soak the bottom of the tray in hot water to help it release the frozen product. In the end, I discarded the ice cube tray idea, because it created chunks that were thicker than 1/2”, which didn’t work very well under the standard programming. The product creates a light and airy structure that also works as a great insulator. Harvest Right is correct when they list 1/2” as the working size of product, because even after eight hours of drying cycle time, the center of the cubes still contained frozen product.
Oil-based products do not work well at all. I attempted to freeze dry butter, figuring that since butter will freeze hard it has at least some water content in it. As the heaters kicked on to begin the process of drying the butter, it seemed to work as I watched for about 10 minutes. Then the butter melted into a liquid product and proceeded to boil violently, spraying melted butter over the entire interior. That was a spectacular failure that required about an hour of cleanup. Do you have any idea how much soap is required to clean up 1.5 pounds of butter? I do. It isn’t pretty. As messy as that was, it provided valuable insight into just how easy the unit is to clean. The vacuum port, along with the measurement ports, are on the upper half of the chamber, so they rarely get dirty. In this case, I was able to wipe out any melted (then congealed) butter with a hot soapy cloth. The drain, on the other hand, presented a problem; it is on the bottom of the unit. Several repeated applications of boiling soapy water had to be sent down the drain, followed by cleaning with a nylon brush (from my camel-back cleaning kit) to remove the butter from it. In the end, we were able to clean the entire unit up in a little less than an hour, though there were two people working on it– one cleaning trays and the tray holder while the other was cleaning the unit itself.
There were some things about the unit that bothered me. This unit is retailing for about $3899.00, which is an incredible price considering what it does. However, I was annoyed with the riveting of the tray holder assembly. As we used the unit, and especially as we had to remove the tray holder to deal with the failures and cleanup, the rivets loosened up and the tray would eventually rock back and forth nearly 1.5 inches. It doesn’t affect the operation of the unit in any way, but I expect an assembly to be sturdy enough that there is no movement unless it is intended. In my case, it irritated me enough that I drilled out four of the aluminum rivets and replaced them with 1/4” #4 stainless machine screws and nuts. It’s an easy fix.
The second worst irritant is the exit of the drain tube. The tube attached to the drain port of the chamber is re-enforced vacuum hose, which is rather stiff. You have to route that hose out from under the unit in the rear (because it isn’t long enough to exit anywhere else). The hose then connects to a 1/4 turn valve, which you open to drain the unit and close to operate. The valve assembly is too close to the unit, and if you do not have the rear feet lengthened enough, the weight of the unit will mash the valve assembly into your counter marring its surface and possible damaging the valve. The tubing supplied on the other end of the valve is too short to reach the ground if you are setting on a counter, necessitating the use of a stool to place the bucket to catch the melted water when you drain it. Also, if you are setting the tube in a bucket, you need to make sure that the end is above the water line of any water left in the bucket. If you forget to close the valve when you are cycling the machine, it will suck up anything in the bucket back into the chamber and spray it all over your product. Don’t ask me how I know this. It was a painful loss of food.
Another item that bothered me was that the system simply shuts the vacuum motor down by shutting off the power to the pump. The pump manufacturer recommends against that type of shutdown, as the pump is still under a vacuum, and the loss of power means that the oil gets sucked back into the cartridge, making for a hard start the next time. The pump never failed due to this, but you could hear the pump work hard to spit the oil out of the mechanism before starting to pull a vacuum. In some cases, the pump will stall several times before running due to the oil. The manufacture also states that this is hard on the plastic coupler between the motor and the pump. You can, however, mitigate this with some simple oversight in the operation, but that removes the “push the button and go” feature of the freeze dryer.
I also had a failure of the electronic display on the unit I received, but the company was very responsive in getting it fixed. They sent the replacement directly to me with the instructions of having a refrigerator repair man install it and bill them. However, it was a simple matter to replace the display, so I did the work myself.
I had the unit apart to repair the shipping damage and then again when I replaced the display. While most electrical connections are made by crimp connectors, I was disappointed to find the power connectors soldered and then simply wrapped in electrical tape. I would expect nothing less than heat-shrink wrapped solder connections in a unit that I am paying several thousand dollars for.
It wouldn’t be hard for Harvest Right to fix any of these irritants, though some, such as the vacuum motor, might affect the cost of the unit. The drain tube would have been better with the valve mounted to the unit and the hose exiting through the casing rather than under it.
Did I mention that you can freeze dry your own products? Let me list the top three benefits of owning this machine in order of importance:
- You can freeze dry your own products (determining your family’s preferred quality and content).
- You can freeze dry your own products!
- You can freeze dry your own products!!
Seriously, I can’t think of a more compelling reason to own this unit. You can freeze dry ingredients (carrots, meat, potatoes, fruit, et cetera) or you can freeze dry meals (your favorite stew and casseroles), including only the ingredients that your family prefers or needs for dietary purposes. You need less salt; no problem! You have a gluten, onion, or dairy intolerance; no problem! You despise celery; no problem! You can have complete control, even to the point of growing your own organic food and freeze drying it to preserve the nutrients and fiber better than if canned. Plus, my family reminds me that this is the only way they can get their “ice cream fix” when there is no electricity. My wife says she cannot be sweet without her daily sweet intake. So, I am freeze drying ice cream sandwiches simply for her “sweet” disposition.
The irritants were small in comparison to the benefit derived by having this unit. You also have some serious flexibility in what you can use it for. I found that there were very few foods that couldn’t be freeze dried (most being those that have a high oil content, such as butter or peanut butter). You can produce about a gallon of food every 24 hours. If you have a family of six and freeze dry only those things that require refrigeration or freezing (or canning) for long term storage, you can actually make this a part of your long-term food storage and be able to freeze dry your larder as fast as you use it. This, of course, means that products like wheat, pasta, rice, and beans are not freeze dried, but meats, fruits, and vegetables are.
With only one of these units, the freezer becomes a short-term preparation and holding area as you feed the freeze dryer. My calculations show that if you have a one-year larder for a family of six and you freeze dry all foods that you would normally can, dehydrate, or freeze, you would be running it about six months out of the year. If you supplement by dehydrating foods that don’t need to be freeze dried, you may even be able to run it three to four months out of the year. Of course, to get in that position, you will end up running it 24/7 until you have attained that position. In addition, if you calculate in the cost of running the freezers and canning equipment for a normal larder, you come very close to break even expenses. Three freezers are not cheap to run year round.
One of the most common questions I received as I reviewed this unit was about the cost of owning and running it. For the purposes of these calculations, I will use current food prices at Costco (2014) and a 10-year lifetime on the unit. In addition, we had previously purchased many Honeyville freeze-dried products because of their reputation of having high quality product, so I compared my product from the Harvest Right freeze dryer to the Honeyville products I had on hand.
- First, we have to calculate the ownership cost of the unit. If you purchase at $4000.00 and use it for 10 years (the standard lifetime of kitchen appliances), your cost is $400/yr or $1.09/day.
- The unit uses oil in the vacuum pump. You don’t change it because it breaks down, but you must change it due to contamination issues. The more contaminated the oil is, the harder it is to pull a vacuum. For our purposes, I’ll assume you do not have the ability to recycle and clean the oil. Locally, O’Reilly Autoparts store sells the oil for $22/gallon. On average, you will use one gallon/month if you routinely change the oil once a week. (See the tips and tricks on the next post to find out how to extend the life of the oil.) That makes the cost of the oil $0.73/day.
- It also requires electricity to run the unit. There is a compressor and a one HP motor on the vacuum pump. (The electronics use a negligible amount, so we will ignore them.) The unit states that it uses 10 amps, but that is a worst case number. The vacuum pump will not require the full 1hp when the high level of vacuum is reached and will also only run about 2/3 of the time, unless you pre-freeze your food. My current electricity is $0.09/kWh, so if the 10 amp figure is used (worst case) I use $2.60/day, though the real amount is probably closer to $1/day.
That means the unit costs $4.42/day to operate, including cost of ownership, worst-case oil usage costs, and worst case electricity usage costs. In 24 hours, the unit will produce roughly one gallon of food. One of the first foods that we produced was freeze-dried egg crystals, similar to Honeyville’s whole egg crystals. We were able to produce a #10 can with 96 purchased eggs for $13.87 compared to Honeyville’s $36.99. In addition, you can use your own chicken eggs to further reduce the cost. You also have total control over the quality of the product, and the resulting product shows it.
I produced a #10 can of freeze-dried cheddar cheese for $19.93 compared to Honeyville’s $43.89, and my product was considerably better in both texture and taste. A #10 can of sour cream cost me $10.89 versus Honeyville’s $22.49, and the product was indistinguishable from the fresh product whereas Honeyville’s product was merely edible. Berries on the other hand, were just about break even on the cost with Honeyville’s product, but my end product was superior in taste and texture. (On both accounts the superior results were probably because we used a higher quality fresh product than Honeyville.)
Have you ever made a large meal and then had to throw the leftovers out a week later? I admit that is a rarity with two teenage boys around here, but it has happened. You can only refrigerate the leftovers for a few days. However, you can extend the storage time by moving it to a freezer, but then you take up valuable space there. This unit will allow you to simply freeze dry the leftovers and use them off your pantry shelf at your leisure.
In a heartbeat! After having played around with it for a month, I can see that in both cost of food storage and quality of food storage, this is the way to go. I will be purchasing one of these units, despite some of the rough edges. I am confident that the company will work out the minor issues that bothered me, and those issues that would affect the bottom line price of the unit can be dealt with by simply managing the unit rather than letting it run as intended. Of course, if you don’t want to bother with it, it will run just fine by loading it and pushing the button.
You can check this unit out at Harvest Rights web page along with several other nifty products they produce.
This is a three part review:
- Part 1 – The background and initial impression.
- Part 2 – How it works / First operations / Overall impression
- Part 3 – Tips & Tricks for Optimal performance / Recipes