Preserving the Future: The Science of Food Dehydration
Dehydration is one of the world’s oldest methods of food preservation, with the principles of this process influencing some of the most modern methods of food science. Read on to discover the ancient history of dried foods.
The ancient technique of dehydrating food
How stuff works. “How dehydrated food works.” Accessed 2nd November 2019.
Geography plays a crucial role in food preservation methods, which is why sun-dried foods are integral to certain cultures. Historical evidence indicates that Middle Eastern and Oriental cultures practiced food drying as far back as 12,000 BCE. By around 2,800 BCE, the ancient Egyptians were using sun-drying techniques to preserve fish, poultry, dates, and raisins for long-term storage
. Similarly, during the Middle Ages (approximately 630 CE to 1630 CE), people in Mexico and Peru relied on sun-drying to preserve cocoa leaves and fruits.
Some of the ancient dehydration methods are still the best ones - take, for example, sun-dried tomatoes. After being cleaned, sorted, and pretreated with sulfites, halved tomatoes are laid out on wooden drying trays in the sun for 9 to 14 days.
The Produce Nerd Youtube channel. “How sun dried tomatoes are made.” Accessed 2nd November 2019.
Compared with mechanical alternatives, sun-drying tomatoes is still the best method for preventing nutrient loss and allowing flavors to concentrate.
The first food dehydration machine
The first automated drying process was created in 1795 by French inventors Masson and Chollet. The machine fed sliced fruit and vegetables into a hot-air dehydration chamber, with a controlled temperature of 40°C, dehydrating produce ready to be pressed and sealed in tin foil.3
Encyclopaedia Britannica. “Food preservation: Dehydration”. Accessed 2nd November 2019.
Since then, various techniques for dehydrating food have been developed. Here, we will examine how two of the most common drying methods work.Spray drying food
The dairy industry is one of the largest processors of dehydrated food. Many dairy products are spray-dried, meaning they are atomized into a fine mist and then brought into contact with hot air. The moisture is instantly removed, leaving only the milk powder as a product. This method is used to make powders
such as milk, whey , and yeast, as well as some ice creams, cheese, and fruit juices. Although spray drying food gives you the product quickly, it is a very expensive technique requiring a lot of energy.
The watery part of milk that remains after the formation of curds.
Freeze drying food
When food is frozen, the moisture within it turns into ice. The food is then placed in a vacuum at a temperature of -45°C, where the ice is removed through sublimation—a
process in which it transitions directly from a solid to a gas, bypassing the liquid phase entirely. This method preserves the food's structure and flavor, and it can be applied to almost any type of food for freeze-drying.
How stuff works. “How dehydrated food works.” Accessed 2nd November 2019. Like spray drying, however, this method can also be expensive. To make up for high production costs, it is mainly used on high-value consumer products, such as coffee.
Pros and cons of dehydrated food
Food dehydration reduces the size and weight of the food while keeping some of its nutritional content. For example, if you dry 9.1kg of plums, you will get 1.1kg of prunes. This makes it much easier to transport and store, not to mention an amazing longevity of 6 months to a year, compared to a typical 3-5 days for a fresh plum.
So, what are the downsides? Firstly, dehydrated food has a bad reputation for changing the flavor of food, often not for the better, as well as creating a tough and leathery texture. On top of that, many foods lose vitamins and other valuable nutrients in the process. For example, apples, apricots, peaches, and plums lose 6% of their vitamin A, 55% of thiamin, 10% of niacin, and a massive 56% of their vitamin C when dried.
Retaining nutritional value
On the other hand, if you were to measure the amount of nutritional content by weight, then dried foods have the advantage over their fresh counterpart.
It is much easier to eat ten dried apricots than ten fresh apricots in one sitting. So, the sheer quantity you can easily consume may make up for lower levels of nutrients per fruit. Added calories and fiber also make it a firm favorite among campers and those going on long expeditions.
When preserving fruit, it is common to use a sulfur gas or sulfite dip prior to dehydration. This helps slow down oxidation, which causes the fruit to darken, and also reduces the breakdown of vitamins A
and C during the process.
Fun Fact: Since the early days of space exploration, dehydrated food has been a key part of astronauts' diets. For instance, during the 1965 Gemini mission, crew members rehydrated freeze-dried foods such as chicken soup and butterscotch pudding using a water gun.
Despite its sometimes negative reputation, dehydrated food remains a staple in our diets thanks to its simplicity and effectiveness in food preservation—and it will likely continue to play an important role in the future.
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