How Do I Store Dried Fruit?
Dried fruit and dehydrated fruit can be preserved by following some simple rules that take into account the nutritional characteristics of the products and the conditions of the environment in which they are stored. In this article, we explain step-by-step how to preserve your favorite dried and dehydrated fruit best.
What Happens In Production?
The shelf life (this is the period during which the product maintains its qualitative characteristics under normal conditions of storage and use) depends on various factors that concern both the specific aspects of the fruit as well as the nutritional attributes of the food and the water content inside it (aw) and the external variables, for example, the temperature, the relative humidity (RH%) of the storage environment, the exposure to light and oxygen, the processes of processing to which they are subjected (drying, roasting, etc.), and any infestations (insects, mites, cockroaches, moths).
These two types of factors work together, so both must be taken into consideration for optimal food preservation. Estimating the shelf life of a food is often difficult because it depends, above all, on the way in which the product is stored.
There are differences between dried fruit (e.g., hazelnuts, pistachios, walnuts, cashews, pine nuts, etc.) and dried or dehydrated fruit (pineapple, coconut, mango, dates, berries, etc.):
Dried fruit is mainly made up of seeds, which are well supplied with oils (defined as lipids), which act as an energy reserve for future seedlings.
These lipids are mostly made up of unsaturated fatty acids, which quickly undergo souring and rancidity. The speed of oxidation, which gives rise to rancidity, increases as the quantity of polyunsaturated fatty acids increases. For example, walnuts that contain more of them are more subject to oxidative phenomena compared to hazelnuts, which contain less of them, in favor of a greater quantity of monounsaturated fatty acids, which makes them have more excellent resistance to oxidation.
Dried fruit, on the other hand, has only been stripped of most of its internal water, so it consists mainly of simple sugars and fiber. These sugars can undergo caramelization and the Maillard reaction, which imparts a dark color (called browning). Proteins can also take on a brown color and become more challenging due to the loss of their ability to reabsorb lost moisture from the environment.
The relative humidity (%RH) of the storage environment influences the available water content inside the fruit. If it exceeds 65%, the seeds tend to reabsorb water from the atmosphere, promoting enzymatic hydrolytic souring caused by lipase (enzymes that “break down” lipids). The resulting release of fatty acids facilitates auto-oxidation phenomena. High RH contents also modify the mechanical resistance of the seed, which loses turgidity and takes on a rubbery consistency.
On the contrary, too low RH contents (around 20% or lower) cause the roots to lose excessive weight, which becomes fragile and easily damaged during handling, in addition to the fact that extreme dehydration promotes lipid oxidation. Excessive humidity also favors the onset of mold (especially of the Aspergillus spp. genus), which produces aflatoxins (AF), hepatotoxic and immunosuppressive substances. Of all the aflatoxins, the most dangerous is B1, the most potent natural carcinogenic substance known.
- It conditions the growth of mold; they grow best between 6 and 46°C.
- It is helpful in containing the risk of infestations; many are of subtropical origin, so very low temperatures are poorly tolerated by pests.
- It keeps the bacterial load under control; most bacteria prefer environments where the temperature is between 20 and 40°C.
- Increasing the temperature increases the speed of a chemical reaction, so lowering the temperature means decreasing the rate at which food decomposes.
Exposure To Light And Oxygen
For the growth of strictly obligate aerobic bacteria, the presence of oxygen is necessary. To overcome this problem, the fruits are packaged in a modified atmosphere, removing the oxygen and using inert gasses in their place, for example, N2. Furthermore, in normal conditions, oxygen would react with some components of foods, modifying their organoleptic characteristics; thus, using N2 slows down browning and rancidity, keeping the aroma of the fat fraction unchanged. Some substances are photosensitive and, therefore, degradable to light; furthermore, light is one of the leading causes of oxidative alteration. When stored in the dark, a drastic slowdown in lipid oxidation phenomena was detected despite the ambient atmosphere.
When Does Dried Fruit Expire? Difference Between “Use By” And “Preferably By”
If stored correctly, dried fruit and dehydrated fruit preserve their qualities for a long time. Naturally, these products also have an expiration date, which is indicated on the packaging by the words “preferably by.” The term “preferably by” offers a certain flexibility compared to “use by,” leaving open the possibility of using the product even after the indicated date and evaluating the conditions of the product itself.
This means that, within the expiration date, dried and dehydrated fruit preserve their qualities to the maximum and, if stored correctly, can be consumed even after this date. They, therefore, differ from products that are “used by” the expiration date or that must be used before that specific date to guarantee the safety of the food.
What Can Be Done To Preserve Dried Fruit At Home? Follow These Simple Rules:
After purchasing nuts and dried fruit that you intend to keep for a long time, the rule is to place the fruit in cool, dry places in the dark, away from sources of heat and humidity. Here are some tips for best preserving dried fruit and dehydrated fruit:
- The ideal storage condition is in a refrigerated environment, whether it is a packaged or unpackaged product; refrigeration, in fact, extends the shelf life of the fruit for up to several years. The product can also be stored without problems at room temperature during the winter season, given the low temperatures. During the summer, however, it is advisable to keep the product in the refrigerator or the most excellent possible environment, as rising temperatures could cause the products to deteriorate.
- The ideal container in which to store them is glass. Thanks to its constitution, in fact, it is impenetrable to chemical and gaseous agents, and having excellent thermal insulating capabilities, it maintains the initial temperature for a longer time than other materials. It is also made up exclusively of mineral salts, so there is no risk of the release of organic materials. If the glass is colored, so much the better: by using colored glass, specific wavelengths of light (including ultraviolet) are prevented from entering, and therefore, some nutritional and organoleptic characteristics remain unaltered. They also come to our aid if the product is in less than ideal conditions, for example, exposure to heat or the sun.
- The type of closure of the container is also necessary: an airtight cap ensures that the food is protected from excessive contact with oxygen, which can lead to lipid oxidation and be essential for aerobic bacteria.
- It is always a good idea for the environment to be well-ventilated. By ventilating the rooms, the internal humidity that escapes from the windows is kept under control, guaranteeing the right balance, which helps to prevent the onset of mold.