When it involves the fundamentals of freeze drying, fruits have many traits that make them as difficult as meats or mixed-ingredient meals when processing. From enzymatic browning, distinctive traits. moisture adsorption and sugars altering the glass transition temperatures of fruits, many variables require a bit of additional preparation and a spotlight.
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Give me some sugar!
So the most important distinction between fruit and greens when contemplating them as foodstuffs, not botanical objects is the upper degree of sugar content material. The great present of sweetness is one thing appreciated out on the path, on the workplace, and even simply on the sofa whereas watching Abbott Elementary.
Unfortunately, sugar’s great style provides issues when freeze drying meals as micro organism can survive lyophilization. Sugar can change the speed and length of freeze drying, in addition to the necessity for instant packing to forestall moisture adsorption.
It’s a sophisticated course of the place I’ve spent hours studying Moisture sorption isotherm ratios, the completely different glass transition temperatures of varied fruits to get one of the best taste, in addition to enhance look of an finish product. All of those matters have been researched to the purpose the place there are scientific fashions and theorems for a way most meals will or won’t react.
It’s an actual rabbit gap when you’re actually concerned with ensuring your strawberries not solely stay tasting nice, however don’t seem deflated or squished as soon as freeze dried. Heck, freezing methodology may even impression rehydration effectiveness.
Moist, Moist, Moisture
So because of the properties of many plant cell partitions being hydrophilic along with excessive sugar content material meals being considerably extra hygroscopic than say, inexperienced beans or corn, further properties are wanted to make sure the meals you simply spent 25-40 hours freeze drying don’t find yourself soggy earlier than they’re positioned in packaging.
I’m positive massive services have humidity managed rooms the place even when present topside temperatures have been 91 levels with an estimated excessive right this moment of 105, they’d hold rooms the place meals is processed maintained at 68 levels with zero humidity always. This is likely to be why there are a number of freeze drying firms in dry areas like Utah and New Mexico?
In your individual dwelling, operating a dehumidifier within the room the place you’ll be taking meals out of the freeze dryer and vacuum sealing luggage is critical. My kitchen sometimes runs 55-62% humidity, however I can get it to 30% if I hold my dehumidifier operating continuous.
When placing meals in luggage, both mylar or vacuum sealed luggage, it’s at all times secure apply to extend the oxygen absorber’s dimension by about 50% or extra. Normally, for a tray of freeze dried apple slices weighing 4 to 5 ounces taking over a 6″ x 10″ x 2″ bag area earlier than sucking air out, I’ll place two 200g absorbers in to cut back oxygen and moisture inside the bag. This is doubled in comparison with the one 200g absorber I exploit with asparagus or inexperienced beans of the identical quantity.
Special Techniques – Browning
Some fruits require particular processing earlier than freeze drying attributable to their propensity for browning, or skins/peels changing into powerful after drying. Foods excessive in phenols sometimes endure oxidation as soon as bruised or minimize into items. We all have seen lettuce, apples, and different issues flip brown, proper? Luckily, there are methods to cut back the browning as soon as a fruit (or some greens) have begun processing.
Using temperature can scale back the speed at which meals brown. Some meals work finest when blanching or roasting, however many fruits do finest when saved at low temps that may scale back response occasions of the browning enzymes. At a house primarily based location, one can’t management the quantity of oxygen by means of nitrogen purging chopped up fruit items, however we will deactivate the enzymes chemically.
By chemically modifying the pH of the uncovered meals layers, simply accessible fruit juices like lemon or lime juice can goal the chemical reactions. When shopping for dehydrated apricots on the retailer, sulfites are additionally used, however this compound appears to be culturally undesired as of late.
You know when making guacamole the way it tells you to squeeze a lime in with the avocado slices earlier than smashing it up? Not solely is that for the great tangy taste it gives, but additionally to stop the browning. The ranges of acidity in pineapples may also be used to cut back browning in meals.
Physical Characteristics of Cell Walls
Many fruits within the berry class find yourself wrinkled and never one of the best trying when dried naturally; assume grapes. Scientists have been utilizing sodium hydroxide on blueberries, blackberries, and others to weaken the cell partitions of the pores and skin of the berry to enhance drying occasions in addition to making certain a pleasing mouth-feel of the fruit when eaten in dry kind or reconstituted. I learn in a analysis article from NASA that they positioned numerous fruits in a 0.25% diluted batch of sodium hydroxide (lye) and water for 30 seconds to make sure berries have been properly freeze dried for Gemini astronauts.
Modern strategies have even included utilizing a CO2 laser to create microscopic etchings of the fruit’s pores and skin to make sure water is launched at a dependable charge.
Since I don’t need to deliver out a small batch of lye, nor do I’ve entry to a CO2 laser that may micro-perforate fruit skins, I bought a self-cleaning flea brush for pets. The wire tines on the underside poke sufficient holes in fruit that it serves the identical function because the costly fruit-specific instrument bought elsewhere. Alton Brown would go right into a uni-tasking tirade if I threw down cash for this factor:
Overcoming Science At Home
Due to my Harvest Right machine not having a supreme degree of choices for tweaking something however length and temperature for freezing and drying, I’m restricted in my choices to maximise water desorption in fruit within the machine. I’ve been in a position to overcome most issues that fruit cell partitions and sugar pose by ensuring the items of fruit I minimize are THIN.
Most if not all the issues I’ve minimize up and caught within the freeze dryer have been beneath 8.5mm (1/3 in.) in thickness. By limiting the scale of the meals, I’m maximizing uncovered floor space and making certain extra water will be faraway from the fruits.
Since even scientists don’t at all times need to need to reinvent the wheel, I’ve discovered that to make sure effectivity and success for many meals within the freeze dryer, it’s higher to chop the items as small as you possibly can moderately make them with out being ridiculous. While slicing a complete watermelon into dice-sized items was tedious, the efforts resulted in 2630g (5.8 lb) of watermelon efficiently freeze drying in 34 hours (beginning at room temperature).
In Summary
While some meals could require much less focus or precision earlier than placing into the machine, I actually imagine any and all precautions to make sure an important product are price their time with regards to freeze drying fruit.
Be positive to:
- Maximize your time reducing up meals to stop browning.
- Use citrus juices to stop browning.
- Ensure all utensils, trays and different factors of contact are sterile
- Reduce publicity time as soon as faraway from freeze dryer
- Use extra moisture/oxygen absorbers than volumetrically anticipated.
- If potential, scale back the humidity of processing location as finest as potential.
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