When you think of freeze-drying, you probably think of outdoor food instantly, right? But have you ever wondered what is actually involved in getting the food dried and ready for you to rehydrate? Well, read on to find out what is involved with drying the food and why it is such an excellent option for the food we take adventuring.
I guess the place to start really is a little bit of the history of freeze-drying. You can trace freeze-drying back to the 15th century in its most basic form. The Inca people would store their crops in the mountains above Machu Picchu. The freezing cold temperatures and the low air pressures led to the moisture slowly turning to vapour and leaving the food effectively freeze-dried.
The modern techniques were developed during World War 2 due to a lack of refrigeration when transporting blood from the US to Europe for the wounded soldiers. It was then developed commercially for the medical field. NASA then made the freeze-drying process widely popular when it wanted Ice Cream in space in true American style.
So, “What actually is freeze-drying?” Well, simply put, the food is frozen and then dried, right? There is actually a little more to the process. So, let’s see what that looks like;
1—First, the food is frozen; however, it is frozen to minus 50°C. This is to ensure all the water is frozen in the food.
2- The pressure in the freeze dryer is lowered to about 600 millibars. For some context, that’s about the air pressure at the summit of Aoraki/Mt Cook.
3—Now that the food is very frozen and the air pressure has been reduced, it's time to warm it up. Because the pressure is so low, the moisture in the food doesn’t melt. Instead, it sublimates. This is where the water content turns directly into vapour, kind of like steam, only much colder.
4- With all the moisture now gone, the food continues to be warmed, and the pressure increases again. The food is usually then put through a secondary drying process to ensure all water has been removed.
The freeze-drying process is the best way to maintain the food’s natural structure and nutrition content. Freeze drying keeps about 97% of the nutrients in the food, whereas traditional drying keeps only around 80%. Another significant benefit to freeze-drying is the rehydration time. It takes about 10-15 minutes to fully rehydrate a freeze-dried meal, whereas a meal that has been dried traditionally takes up to 2 hours.
These time savings and the benefit of retaining 97% of the nutritional content make Freeze-dried food a great choice for adventures. More than other food methods, Although it may cost a little, it is so simple and lightweight that it makes sense to go adventuring with freeze-dried food on the menu.
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