Dehydrating fruit/veg, temperature, and safety
I have a food dehydrator, which I've used in the past for chillies, apples and herbs. I intend to dry some tomatoes with it soon, a process that apparently takes about 8 hours at 60°C (140°F) (it actually took considerably longer in my case). This temperature is exactly at the top of the US FDA's danger zone and is unlikely to be maintained in an entire dehydrator with a thermostat in the air stream. Dehydrators also allow lower temperatures to be used (mine does 35–70°C). Sun-drying tomatoes takes place at an uncontrolled temperature, which we can assume is sometimes ideal for bacteria/mould growth. Apple rings are often dried cooler and take 12+ hours.
These are sliced/halved fruit/veg, so aren't protected by their skins; they wouldn't dry if they were (as I found with blueberries). And for much of the process they're rather wet. The pH is usually uncontrolled; apple slices may be dipped in lemon juice but only to keep them from turning brown.
So why don't we get mould/bacteria growth during the dehydration process?
Best Answer
Food doesn't spoil because pathogens need moisture to grow. If you put too much food in a dehydrator, it won't dehydrate and will spoil.
According to the USDA the following is needed to ensure food safety when dehydrating.
- the process must be fast enough to dry food before it spoils; and
- it must remove enough water that microorganisms are unable to grow
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Quick Answer about "Dehydrating fruit/veg, temperature, and safety"
Place trays in a preheated dehydrator. Initially, the temperature can be set at 145°F when there is surface moisture on the fruit or vegetable. After one hour reduce the temperature to 135 to 140°F to finish drying.What temperature is best for dehydrating vegetables?
The optimum temperature for drying vegetables is 140\xb0F. If higher temperatures are used the vegetables may "case harden", that is cook and harden on the outside while trapping moisture on the inside. The vegetables will eventually mold when the moisture equilibrates in the item.What temperature should a fruit dehydrator be set at?
Follow your dehydrator manufacturer's recommendations for time and temperature. No manual? Set the temperature between 125\xb0F and 140\xb0F. Dehydrating at 125\xb0F will result in a more evenly dehydrated end product, while setting the temp to 140\xb0F will make everything go a bit faster.What temperature is best for dehydration?
Many culinary techniques make use of food dehydrators. Most foods are dehydrated at temperatures of 130 \xb0F, or 54 \xb0C, although meats being made into jerky should be dehydrated at a higher temperature of 155 \xb0F, or 68 \xb0C, or preheated to those temperature levels, to guard against pathogens that may be in the meat.What happens if you dehydrate food at too high a temperature?
You can dry some foods at too hot of a temperature where it depletes many of their nutrients. Herbs should not be dried at higher than 115\xb0F / 35\xb0C in most cases. You don't want to dry fruits at 165\xb0F/70\xb0C which can cause case hardening.How To Dehydrate -- Everything you need to know to safely dehydrate fruit and vegetables
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Answer 2
where you need to be very careful about the amount of moisture in the air. water should be possible at a minimum. It would also be extremely good if you can provide a dry air flow that goes through for a long time to dry. The presence of any molds can be controlled by magnifying glass.
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