Updated: Apr 3, 2021
NULL HYPOTHESIS 12 (Apples): Blanching Apples for 30 seconds before freeze-drying will not affect taste compared to uncooked
Conclusion: We Rejected this Hypothesis
Abstract: We blanched one batch of apples (Macintosh) and left another batch raw. We froze all of them and then freeze-dried them. Our test subjects tried the raw freeze-dried apples and the blanched freeze-dried apples. Three of our four testers could tell a difference in taste between them. Although not relevant, our testers could not identify the apples only note that they tasted different.
Appx. 3 - fresh apples
1 Harvest Right freeze dryer tray with a silicone mat
Pot for steaming
A metal strainer to hold the apples over the boiling water
1 qt. water
Bowl of ice
Above: The top photo is of fresh apple slices before freeze-drying (left third is blanched, right two-thirds are unblanched). The bottom photo is of freeze-dried apple slices (left third is blanched, right two-thirds are unblanched).
Boiled the water in the pan.
Put a third of the apple slices in the metal strainer.
Held the strainer over the boiling water for 30 seconds.
Drained water off apple slices and placed them in the ice.
Once cold, set the apple slices out on the tray.
Set the unblanched slices out on the tray.
Froze both trays overnight.
Started freeze drier on the non-liquid, pre-freeze setting (waited 30 mins.)
Once the pre-freeze cycle completed, placed the frozen trays in freeze-drier (with 3 other trays of food; we did two trays of oranges and one tray of skittles)
Started the freeze-drying cycle.
Removed apples from freeze-dryer
Taste-tested the slices.
Our actual total starting weight of apple slices on the tray was .564 kg and the finished weight was .093 kg (not including the tray itself).
The freeze-drier completed its ordinary cycle at 20 hours. We added 12 hours because it would have ended in the middle of the night. The temperature scanner showed an approximate average temperature of 94° F. We did not find any cold spots.
When I compare them, the freeze-dried apple slices look almost indistinguishable, which is consistent with the appearance of the original apples before freeze-drying.
We only had four blindfolded testers. One could not tell the difference between the blanched and non-blanched freeze-dried apples. The other three testers reported they could tell a difference. None of our testers could tell which apples were blanched and which were not. None of our testers could identify what was different about them. Our kids reported that the blanched apples tasted crunchier and the blanched apples tasted sweeter. We did not have enough confidence in our taste testing to confirm whether blanching 30 seconds makes a noticeable difference in apple slices once freeze dried.
Although not relevant, I see a slightly improved appearance in the blanched apples (on the right third of the tray). We probably would not blanch apples in the future before freeze drying because it seems to be more trouble than it is worth.