Dehydration methods and dried fruit processing equipment

Prepping and sulfuring the fruit

Fruit needs to be prepped before drying and the basic steps of the pre-drying process are selection, sorting, washing and, in some cases, peeling and cutting the fruits.  Another important step in the pre-drying process is color preservation, commonly known as sulfuring. Most fruits are treated with sulfur dioxide (SO₂), which slows the deterioration of the fruit’s browning, which happens when enzymes are not inactivated by the heat used during drying. Moreover, it helps preserve the carotene and ascorbic acid found in the fruit.

Sulfur dioxide is used widely in dried fruit manufacture, but it is good to note that it can negatively affect people with asthma if they ingest it in large quantities. The FDA, for example, requires food and snack manufactures to disclose the presence of sulfiting agents on the label if it is in concentrations of at least 10 parts per million.

Freeze-dried vs dehydrated fruit

While dehydrated fruit still has about 30% of its initial moisture, freeze-dried fruit retains only 1 to 4% of its original moisture. The water content gives the dehydrated fruits a chewy and sweet texture. On the other hand, the freeze-drying method leaves tiny air pockets in the fruit creating a light, crispy texture in it. This happens because the water escapes from the fruit in the form of gas.

Regulations and international standards for dried fruit

There are important regulations and international standards all manufacturers of dried fruit must comply with in order to export and sell their products.

Strict controls are implemented on the amount of aflatoxins. The FDA requires that levels of aflatoxins for nuts and dried fruit be below 2 μg/kg for aflatoxin B1, and below 4 μg/kg for the total aflatoxins content.

Conductive multi-flash drying method

Food scientists Jade Varaschim Link, Giustino Tribuzi, João Borges Laurindo published in the Journal of Food Processing and Preservation a new study for fruit drying in 2017. The study stems from the fact the short shelf life of some fruits limits their commercialization as fresh products. Their study focused on the drying process as well as the physical and structural properties of their samples and how they reacted to different drying methods. They also compared nutritional and rehydration properties of dried fruit.