The scientific principle of dehydration is rooted in the physical process of removing moisture from food, which plays a crucial role in preserving and enhancing its characteristics. By reducing water content, the growth of bacteria and microorganisms responsible for spoilage is inhibited, extending the shelf life of the food. This method not only serves the practical purpose of preventing decay but also concentrates flavors, nutrients, and textures. Whether accomplished through traditional sun-drying methods or modern technologies, the scientific principle of dehydration underscores the importance of moisture removal in maintaining food quality, making it a cornerstone in both culinary and preservation sciences.
As food is dehydrated, mass and heat are transferred both inside the food itself and between the food and the medium used to transmit energy to the food. Air or another gas may be needed to transfer moisture away from food in food dehydration techniques that deliver energy to the food using media other than hot air.
There are three main categories of processed foods that may be defined by the value added during the drying process. Very little is gained by processing a ton of grains, legumes, or roots. A ton of rice that has been artificially dried is not much more valuable than a ton of rice that has been sun-dried on mats at the farm. Drying such crops is only cost-effective at extremely large scales in silos or in locations where solar drying is absolutely impossible owing to rain or excessive humidity.
High-value crops like spices, herbs, medicinal plants, and nuts contribute a lot more value per acre than other crops do. Products with adequate value added from small- scale processing to cover expenses and earn a profit are best suited for small and medium-sized businesses.
Most fresh foods have a moisture content of between 70 and 95 percent, and it is this water that promotes the growth of molds, yeasts, and bacteria, ultimately leading to deterioration. There is insufficient moisture to enable micro-biological development if the moisture content is lowered to between 5 and 25 percent (depending on the kind of food). Yet, the micro-organisms are not destroyed; rather, they go into a latent state and wait for the moisture content to increase so that they may resume their multiplication. Thus, sturdy packing is essential.
There is a large range, maybe up to 25 percent, in the amount of moisture decrease required to preserve a particular meal. This is due to the fact that the total quantity of moisture accessible for microbial development is more important than the actual amount of moisture in a meal. Sugars and salt, for instance, may chemically hinder water, making it inaccessible to micro-organisms; this is why fish and meat are often salted and why certain fruits are sugared before drying.
Enzymes, which are a normal element of all living things, play a role in the spoilage of certain foods, especially those high in fats and oils, by causing rancidity, color loss, and flavor alterations. The pace of such enzymatic processes may be slowed by decreasing the commodity's moisture content, hence increasing its shelf life.
However, the micro-organisms are not dead; they are just latent until the moisture level rises again, maybe as a result of rewetting through atmospheric absorption.