Reprinted with permission from the 54th Annual Report of the Northern Nut Growers Association, 1963 J.G. Woodroof and E.K. Heaton, Georgia Experiment Station, Experiment, Georgia
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Pecans are semi perishable; they may be held for many years under proper conditions but may become inedible due to mold, insects, staleness, discoloration, or rancidity within a few weeks under unsuitable storage conditions.
Experiments conducted jointly by the Georgia Experiment Station and the Refrigeration Research Foundation have shown that controlled refrigerated storage (a) arrests insects, (b) prevents molding, (c) retards development of staleness and rancidity, and (d) preserves that natural color, flavor, and texture of shelled pecans for as long as eight years. Furthermore, refrigerated storage does not damage pecans even at temperatures as low as -170 F, nor does it increase the rate of deterioration of nuts after removal from storage. This is because the carbohydrate content is low, the moisture content is only four percent and the oil content is about 70 percent. The research data supporting these recommendations may be found in “Pecans for Processing”, Georgia Experiment Station Bulletin N.S. 80.
Storage Advantageous for Handling Large Crops
The 1961 pecan crop in the United States broke all previous production records and stimulated much thinking and planning on procedures for handling the crop. The 221.7 million pound crop was 18 percent above that for 1960 and 46 percent above the 10-year average production. Data on the storage of this crop of pecans were obtained from six companies which operate about 30 refrigerated warehouses throughout the pecan growing area. They reported that 32,817,000 pounds of unshelled pecans were cold stored, while 1,347,768 breakdown given in pounds, were shelled and held in cold storage and in freezers. The breakdown given in pounds was as follows:
UNSHELLED
Cold Storage – 30,734,000
Freezer – 2,083,000
SHELLED
Cold Storage – 1,251,000
Freezer – 96,768
Three companies reported a total demand for 4,085,500 cubic feet of additional space over the previous five-year average for storing 1961 pecans. One warehouse man converted 10 million cubic feet of cold storage space to freezer space for pecans and others extended the freezer space for pecans in 1961.
It was significant that 2,179,768 pounds, or 6.4 percent of the stored pecans, were held at 0 degrees or lower, while only two decades ago freezing was considered both detrimental and impractical for pecans. It was also significant that only 9.3 percent of the total quantity stored were shelled, 9.2 percent of those held in cold storage and 10.4 percent of the frozen nuts were shelled. It is a general practice to store the pecans under refrigeration directly from the orchard and to shell and deliver to end-users as needed.
On the basis of tests at the Georgia Experiment Station, the following requirements must be for long-term storage of pecans.
High initial quality is essential There is a tendency for pecans to deteriorate from the time they drop from the trees. Tests have shown that pecans should be harvested, dried, graded, and stored under refrigeration within a month after harvest. They may or may not be shelled before storage, though shelling has been found to reduce the storage life to one-half. Shelling also reduces the volume and weight to about one-half.
Varieties such as Van Deman, Schley, Stuart, and others that are well filled have a longer shelf life than Tesche, Frotcher, and other poorly filled varieties. It is recommended that only those with good color, texture, flavor, and high oil content be stored for more than one year. The ill effects from improper storage are cumulative and irreversible.
Low relative humidity High moisture in nuts is the cause of more deterioration than any other single factor and may result in nuts becoming inedible within as short a time as two weeks. It is reported that at least 50 percent of shelled pecans in the channels of trade are darker than desired. Most of this high moisture damage is due to (a) delayed harvesting from damp soil, (b) excessive moisture immediately before or after cracking, or (c) storing under conditions of too high relative humidity. Any of these conditions allows the tannin in the lining of the shell to dissolve and stain the seed coats. Once stained, the seed coats gradually become darker due to oxidation in the air. This discoloration has some similarity to the “amber” color due to high temperature storage.
Relative humidity in the air below 32 F is not a problem; but above this temperature, high humidity may be very damaging to the nuts. Shelled pecans, for storage of more than three months, require a relative humidity of 65-70 percent in order for the moisture content to equalize at the desired 3.5-4.0 percent. Unshelled pecans require a relative humidity from 75-80 percent to avoid excessive drying of the nuts on one hand and molding due to too high moisture on the other.
Low constant temperature In general, the lower the temperature the longer will be the expected storage life of the nuts, though there is no critical temperature at which pecans must be held.
At 70 F unshelled pecans may be expected to retain edible quality for six months; with shelled halves, three to four months. Pecans at this temperature are subject to molding, insect infestation, development of “amber” color, staling, and rancidity.
At 47 F unshelled pecans may be held for nine months and shelled halves for six months. The same types of deterioration as listed at 70 F may develop, except that insects are “arrested”.
At 32-36 F the storage life of unshelled nuts may be extended to 18 months and that of shelled halves to one year. Staling and rancidity develop gradually.
At 20-25 F unshelled pecans may be held for 30 months and shelled halves for 1.5 to 2 years without molding, insect damage, discoloration, or rancidity. There may be slight staling and loss of flavor.
At 0 F and below either shelled or unshelled pecans may be held for 6 to 10 years without appreciable loss of quality.
It was found that pecan pieces-large, medium, small, midget, meal-had a shorter life than pecan halves. The reduction in time was in proportion to the surface exposure of the pieces. In general, storage of pecan pieces should be limited to a few weeks or months at temperatures above 32 F.
Because of the low moisture content of pecans, no permanent damage has been found due to freezing to temperatures as low as -170 F. It was found, however, that the temperature of storage should be free of wide fluctuations.
Proper Packaging The unbroken shell of pecans provides abundant protection to the meats in preventing bruising and partial protection against oxidation, insects, molding, and discoloration. Fiber bags or cartons are adequate for storage of whole pecans.
Shelling bruises pecans, which causes the oil to “crawl” over the entire surface of the meats and onto the containers. The amount of crawling and “wicking” of the oil is in proportion to the amount of bruising caused by breaking and cutting. This greasy film becomes stale and rancid much more rapidly than the interior of the meats. For protection of pecan meats the container should have a barrier that is impermeable to air, moisture, and oil. Metal, foil, glass, or flexible films have been found adequate and practical. An antioxidant applied to the inner surface of the container has been found highly effective, while a wax coating on the interior or corrugated boards was of less value. Crawling of the free oil was least with pecan halves and greatest with the most finely broken pieces.
Odor-free storage room Pecan meats readily absorb odors and flavors from the surroundings. Imperfections in packages permit odors from the storage room, the atmosphere, and other products to be absorbed, resulting in a foreign flavor, odor, or color in the nuts. Even faint odors of wood, ammonia, paint, asphalt, and most fruits and vegetables may accumulate in the nuts and appear stronger than in the surroundings. While aeration or the use of carbon filters are of come benefit, no practical means has been found for restoring such nuts to their original state. Pecans should be stored in a separate odor-free room or only with products free of objectionable odors.
Temper pecans when removed from freezing storage Frozen pecans are very brittle and excessive handling by stacking or hauling may result in considerable breaking of halves. They should be allowed to thaw for a few hours after removal from the freezer and before being shipped. Removal of pecans from refrigerated storage should be in steps of about 15 F each. “Tempering” in this manner reduces moisture condensation and the possibility of subsequent molding and eliminates the likelihood of breakage due to handling while frozen. Tempering pecans going into refrigerated storage is not necessary, but a “certificate of condition” at the time they are received for storage, as well as when they are removed, is highly important.
*An added comment to the excellent article above, with the advent of vacuum sealing machines, longer storage should be easier to achieve. Be sure they are properly dried before sealing. They should be able to be stored in the freezer for an extended period without losing quality.
