How do the 3 different Harvest Right freeze dryers compare in efficiency?
With this test, we chose corn because it’s relatively easy to freeze dry. Corn is generally cheap, which makes it the perfect food to compare against our pork cost analysis. It’s also a simple food item that regularly goes on sale. Needless to say, we picked up a bunch of these bags:
Setting up the test
We tried to eliminate a bias by filling the machines equally based on the tray capacity. After calculating the tray sizes, we determined the correct amount of corn to fill each machine with trays of (close-to) equal densities. As you can see from the sq.in/lb (square inches per pound), we got close. The “perfect” amount might have been more or less than this, but it was a good guess for the test.
It’s interesting to note that the tray capacity of the 5-tray freeze dryer is more than the combined capacity of the 3- and 4-tray units. To be able to compare the total cost, I measured the cost of each freeze-dryer cycle and then totaled each of them. The results are shown in the table below.
Freeze dryer tray capacities shown in the overview table:
Something to note
Our power cost calculations do not include the “Finished” stage, which means that the time between Final Dry and Defrost isn’t included as part of our cost analysis. We leave it out because we could have removed the food exactly when it was finished drying.
See the graph below to see what we mean by the “Finished” stage gap.
Timeline view of the “Finished” stage – between FinalDry and Defrost
Why the gap?
We often leave the trays in either because we aren’t home to remove them, or because the cycle finishes early in the morning. In this case, the cycle finished at 11:20, and we didn’t take the trays out until 4:20.
If you’re curious, it cost us about $0.15 to let the vacuum run for those extra hours.
Table of the calculated efficiencies between the 3 freeze dryer units
* Each column is a comparison of the column before with the 3-tray being the baseline to compare against.
The 4-tray “Cost $ / lb” was 23% more efficient than the 3-tray. The 5-tray “Cost $ / lb” was 10% more efficient than the 4-tray.
The real benefits for the large, 5-tray unit comes from the sheer volume of freeze-dried food you can produce per hour.
Power Cost $ / lb. (at $.10/ KWH)
- 5-tray was $.27/lb.
- 10% more efficient than the 4-tray, and 33% more efficient than the 3-tray
- 4-tray was $.30/lb
- 23% more efficient than the 3-tray
- 3-tray was $.37/lb.
Total Hours / lb.
- 5-tray was 3.62 hours/lb
- 41% more efficient than the 4-tray, and 91% more efficient than the 3-tray
- 4-tray was 5.12 hours/lb
- 50% more efficient than the 3-tray
- 3-tray was 7.67 hours/lb
Overall cost analysis
My cost of the Corn was $1/lb, your cost may vary, I have seen from $.69 – $1.51 and the cost of my power is $0.10/KWH.
Total Cost (Corn + Power) $ / lb.
Dry weight = .2 of wet weight
- Wet – $1.27/lb.
- Dry – $6.35/lb
- Wet – $1.30/lb
- Dry – $6.50/lb
- Wet – $1.37/lb.
- Dry – $6.85/lb
Cost of Commercial FD Corn in #10 can
The best price I found for freeze dried corn on the internet was $17.59 for 1.25 lbs in a #10 can. That comes out to $14.07/lb for freeze dried corn. This price includes the can and an O2 absorber.
Total Cost FD Corn in a 1 pound Mylar Bag
One mylar bag cost $.33 and holds a little more than one pound. The O2 absorber is about $.10. This adds about $.43 to each pound of dry FD corn. You may choose to use reusable jars and save much of this cost, but I will do the cost comparison using Mylar bags.
Total Cost of packaged FD Corn
- Corn $11.25
- Power $ 3.08
- 2 – bags $ .66
- 2 – absorbers $ .20
- Total $15.19 for 2.08 pounds = $7.30/lb
- Savings – ($14.07 x 2.08)= $39.39 – $15.19 = $23.35/batch savings
- Corn $ 6.00
- Power $ 1.80
- 1 – bags $ .33
- 1 – absorber $ .10
- Total $8.23 for 1.16 pounds = $7.09/lb
- Savings – ($14.07 x 1.16)= $16.32 – $8.23 = $8.09/batch savings
- Corn $ 3.75
- Power $ 1.39
- 1 – bags $ .33
- 1 – absorber $ .10
- Total $ 5.57 for .75 pounds = $7.43/lb
- Savings – ($14.07 x .75)= $10.55 – $5.57 = $4.98/batch savings
Individual freeze dryer advantages
- Huge time efficiency advantages
- 23% more $ efficient and 50% more time efficient
- Takes 1.5+ days
- Runs faster than the other 2 machines with small loads
- Great for small loads that need to be done in just over a day
Issues with the test
We got the vacuum error with the 3-tray unit, so the test still isn’t perfect but it’s close enough.
Timeline view of the 3-tray freeze dryer cycle
Notice the pressure drop on rows 521-526. 8 minutes after the pressure drop, the freeze dryer reported a Vacuum Error:
* This is the raw data pulled from the freeze dryer
- We used corn with this test because we were trying to find a food item that might be cheaper to purchase than to do at home
- It’s still “cheaper” to do it yourself at home
- If you need a lot of freeze-dried food, even though it might be cheaper, using the small, 3-tray machine would take a long time to process enough corn for a small family
- Stick with your specialty foods, higher-priced protein (meats) food items
- Special dietary needs are a great use case
- Leftovers are also a good use case for the small unit
- Medium (4-tray) or Large (5-tray)?
- Both are much more efficient than the 3-tray unit
- If you want to build up a lot of freeze-dried storage, the 5-tray is your best bet
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