Pecan nuts harvested in the fall can retain their fresh condition during the next year or until consumed, if handled and stored properly. Good storage helps keep the pecan’s quality. The analysis of a good quality kernel will give a composition of 73–75% oil, 12–15% carbohydrates, 9–10% proteins, 3 to 4% water, and about 1.5% minerals.

A high percentage of oil is indicated by plumpness, crispness, and solidity of kernels, compared with shrivelling, sponginess, and hollowness. High oil content, and the fact that it is highly unsaturated (93%), or cholesterol free, is one of the most important factors, along with water and temperature, impacting the storability of pecans.

Oil

Because oil content in pecans is high, rancidity can develop at warm temperatures and is more noticeable than in most other nuts. Pecan oil is a mixture of several oils, although oleic and linoleic oils are the two principal ones, usually comprising about 95% or more of total oil.

Both the amount of oil and degree of saturation vary with geographical locations. Linoleic acid is the primary chemical component responsible for oxidation and rancidity in pecan kernels. Linoleic acid varies widely in different varieties of well-matured and plump kernels, and it also varies from year to year in the same variety.

Water

Lowering the moisture content of pecan kernels is an important step for maximum storage life of pecans.

Pecans, like many other agricultural products, are harvested at moisture contents higher than those required for storage. Pecans harvested early can contain 25–30% moisture. Water content decreases in pecans harvested later in the season.

Pecans should be stored at a moisture content of about 4%. Pecan moisture needs to be decreased as soon as practical after harvesting. This prevents moulding, discoloration, and breakdown of the oil. Drying pecan nuts was originally done outdoors, by air and sun drying. This process took three to four weeks and moulding often took place in the pecans. Artificial drying or drying with forced air is now used for pecans, speeding up the process considerably and eliminating moulding problems.

Shelled pecans stored at non-freezing temperatures should be maintained in an atmosphere of about 65–70% relative humidity to hold the 3–4% moisture content. Humidity above these values can cause kernel moulding and pecan texture deterioration(pecans become soft and rubber-like), whereas lower humidities will cause excessive drying. In-shell pecan kernels will darken under high humidity as a result of the tannic acid being dissolved from the shell lining.

For vacuum or gas packed pecans, or those stored under freezing conditions, relative humidity control is not necessary.

Temperature

Lower temperatures usually result in longer storage life of nuts. Storage temperatures and predicted storage times of shelled and unshelled pecans are listed in table 1.

Pecan pieces have a shorter shelf-life than pecan halves. This time reduction is in proportion to the surface exposure of the pieces.

Storage of nutmeat pieces should be limited to 1 or 2 months at temperatures about 32°F/0C°. The greatest benefit of storing at low temperature is retention of fresh flavour, followed by colour, aroma and texture.

Because pecan meats absorb odours and flavours readily from the surroundings, a storage area free of odoriferous materials and commodities is necessary. Even faint odours of paint, wood, asphalt, vegetables, and other fruits can accumulate and appear stronger in the nuts than in the surrounding environment.

In-shell pecans can remain good for 4 months at 70°F/21C°, but can be stored successfully for 18 months at 32°F/0C° to 36°F/2C°. Storage life of in-shell nuts may extend to 5 years or more when stored at 0°F/-17C° (table 1).

Table 1. Relative storage life of pecans held at various temperatures

Temperature
In-shell (Months)
Shelled (Months)
70°F/21C°
4
3
47–50°F/8-10C°
9
6
32–36°F/0-2C°
18
12
20–25°F/-6- -4C°
20-40
18-24
0°F/-17C°
24-60
24-60

Burlap bags are satisfactory for holding in-shell pecans if the bags are clean or have been sterilized.

An unbroken pecan shell is one of the best packages for kernels. But, an oil film will form from the broken areas of shelled pecans and spread over the kernels as rancidity develops.

When taking nuts out of frozen storage, thaw kernels slowly; this is called tempering and involves gradually raising the temperature to 45°F/7C° or 50°F/10C° before exposing to a higher temperature. If the pecans are subjected to unusually high temperatures upon removal from storage, moisture will condense on the kernels. Therefore, a series of gradually increasing temperatures is desirable.

It is usually recommended that nuts and nutmeats be stored only in brine or freon refrigerant cooled rooms; however, this may not always be possible. Storage in areas cooled by ammonia refrigeration systems may be unavoidable. Because of the rapid and extreme blackening that occurs on contact with even a small concentration of ammonia gas, leakage prevention is mandatory.

Ammonia damaged nuts and nutmeats cannot be salvaged. The package for shelled pecans must be impermeable to oil. The package should also prevent penetration of air and moisture. Metal, foil, glass, and flexible films are adequate and practical. An antioxidant on the inner surface of the container has proved effective.

At home, pecan kernels may be kept in the refrigerator in a covered glass jar or in plastic bags. In-shell pecans can be stored at room temperature for a short period of time. Keep in a refrigerator, if so desired, to keep for longer than 4 months. If pecans need to be stored for more than a year, either in the shell, cracked, or shelled, they have to be placed in the freezer.

Storage

Before they are marketed, the nuts can be stored at room temperature for as long as half a year. Shelled nuts attain a much higher price than the unshelled nuts, but the processing equipment is very expensive. Most producers market cooperatively or via a processor. After processing, the nuts are usually stored in vacuum-sealed packages, which enables them to be stored for a longer period of time.

Drying

Pecans become discoloured and infected with mould, and their meat quality deteriorates when harvested during wet weather, or under wet soil conditions.To prevent this, pecan nuts are dried soon after being harvested, bringing the moisture level of kernels to around 4.5%. The drying out process aids in providing col our, texture, flavor and also stability to the nuts, which would otherwise occur naturally under field conditions, should the weather and soil remain dry at harvest time. The nuts are dried at room temperature by constant circulation of low moisture air for approximately three days.

Storage

Pecan nuts are semi-perishable in nature and thus require proper drying, packing and storage temperature. Only high quality pecans that have a good size, color, flavor and oil content should be stored, in order to fetch high prices in the off -season market.

Two very important factors that affect the storage life of the nuts are kernel moisture content and storage temperature.It is possible to extend the storage life of pecan nuts, starting from a few months at room temperature to many years at 7.6 °C. Both shelled and unshelled  pecans can be kept at room temperature (21.1°C) for six and three months, respectively.

There are a number of insects and fungi that attack the nuts in storage at temperatures above 7° C. Insects can be controlled by fumigation and fungi growth is prevented by keeping the low moisture level of kernels (3 to 4 per cent).

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