Walnuts, taxonomically, are considered the edible seed of any species of the genus Juglans, of which the majority are found to be edible for humans. With a tough shell and a distinctly savory meat found within, walnuts are popular throughout the world as either a snack or added to dishes as a topping.
However, owing to the high fat content of walnuts, it is not uncommon for them to begin to grow rancid or otherwise degrade in quality over time, especially once removed from their shells and subsequently processed via roasting.
In order to prevent this, many food experts recommend using a variety of storage methods that may extend the shelf-life of the walnuts.
Walnuts may be frozen in order to extend their shelf-life and to combat the eventual spoilage or decay that they will undergo. Whether shelled or unshelled, walnuts are perfectly capable of retaining their taste and texture within the harsh environment of the freezer, especially if insulated by using the proper materials and procedures.
Can Walnuts be Stored in Their Shells?
Much like other nuts or seeds that normally contain shells, the walnut’s own specific shelf-life is significantly longer while still within its shell than it would be outside of it. This is due to the fact that having a solid layer of insulation between the meat of the walnut and the open air or elements will slow down or prevent a loss in quality.
Apart from this, the shell of a walnut will also slow down the ingress of bacteria and fungi, both of which will cause spoilage of the walnut by releasing toxic compounds as they consume the inner flesh of the nut.
However, keep in mind that the exact length at which walnuts still present within their shells will remain unspoiled can depend on a variety of factors. Shelled walnuts that have been toasted or candied may possess a shorter shelf-life than that of raw walnuts with an intact shell.
Is it Better to Preserve Roasted or Raw Walnuts?
While cooking organic foodstuffs is generally known to be quite beneficial for the safety of the consumer as well as tends to “reset” the shelf-life of said food, this is not entirely applicable to walnuts or even nuts as a whole.
Walnuts in their roasted or otherwise cooked form will not last for as long a time as they would in their raw form. This is because of the fact that heat and pressure cause the walnut to leak its own oils outwards, exposing it to the open air and other elements in the storage environment that will cause it to go rancid or spoil.
As such, the ideal form of walnut to preserve is a shelled and raw nut that is immediately stored in your preferred preservation method immediately after purchasing or harvesting.
How Long Do Walnuts Last at Room Temperature?
Because of the low moisture content of walnuts, they may last for a significant length of time in comparison to other organic foods when stored at room temperature. However, if they have been stored in the improper conditions, this relatively long shelf-life will not last as long as it should.
Primarily, the factor one should control the most for is environmental conditions that will cause the lipid compounds present within the walnut to become rancid. These factors are things such as direct sunlight or exposure to air-flow, both of which will cause rapid degradation in the walnuts.
At the absolute maximum, walnuts are capable of remaining shelf-stable for up to four weeks before beginning to degrade in quality or otherwise spoil.
In order to reach this length of time, it is best to store the walnuts within their shells and insulated by an air-tight container. This container must be kept in a dry and cool part of your kitchen or pantry, far from any direct sources of sunlight or moisture.
Can You Refrigerate Walnuts?
Refrigeration is a far more advisable alternative to storing walnuts as the lowered temperatures can act as an inhibitor, both for the eventual rancidity of the lipid compounds present within walnuts as well as the reproductive functions of bacteria and fungi.
In order to store your walnuts properly within the refrigerator, all that is needed is to seal it in an air-tight container with a small amount of space left in order to prevent the walnuts from damaging each other inside the container.
Alternatively, you may also store the walnuts in a resealable plastic pouch and push as much air as possible out of the bag, essentially vacuum sealing it within.
Store this container or bag as far as possible from the crisper drawer, as excess moisture may cause the walnuts to spoil prematurely.
Stored in this way, the walnuts are capable of remaining unspoiled for an impressive twelve months, though it is likely that they will begin to show signs of textural degradation before this point in time.
What Do You Need to Freeze Walnuts?
In order to freeze walnuts in a way that prevents them from growing rancid as they are exposed to the open air or otherwise protects them from the quality degrading effects of being freezer burnt, you will require only a few kitchen staples.
A roll of aluminum foil will act as the first line of defense, both against freezer burn and the open air. Apart from aluminum foil, an air-tight container made of a non odor absorbing material that is also freezer safe will be required. Optionally, you may instead use a resealable plastic pouch or freezer bag in place of an air-tight container.
As always, a freezer with suitable humidity control and an internal base temperature of 32°F or lower will also be required.
How to Freeze Walnuts
In order to freeze walnuts, it is best to choose nuts that are uncooked and still present within their shells so as to extend their shelf-life within the freezer for as long as possible.
Once you have selected the appropriate candidate nuts for freezing, first inspect them for signs of mold or spoilage, as microbial life can quickly spread to other walnuts that are stored adjacent to any rotten or rancid nuts.
Wrap the walnuts in a sheaf of aluminum foil, crinkling it in such a way that no open spaces are left wherein the nuts may be exposed to air-flow that may induce rancidity.
Now wrapped in aluminum foil, place the walnuts in the air-tight container and store in the freezer for up to two years. If instead you have elected to use a resealable plastic pouch or freezer bag, simply place the aluminum foil wrapped walnuts in the bag and push out as much air as possible.
How to Know if Walnuts are Freezer Burned
Though walnuts are somewhat resistant to the effects of freezer burn owing to their relatively low water content and layers of insulation (so long as they remain in their shell), they are still perfectly capable of suffering from this particular side effect of freezing.
The telltale signs of freezer burn in walnuts are much the same as they are when found in other forms of freezer burnt food; namely patches of frost or whiteish ice crystals along the surface of the nuts or on their shell.
The walnuts may also have developed a soft and yielding texture if exposed to the frigid air of the freezer for too long a period. While freezer-burned walnuts are still perfectly edible so long as they do not display any other signs of spoilage, they may be unpleasant to eat or not as flavorful as fresh walnuts.
References
1. Unknown Author. “Walnut (in shell) production in 2019, Crops/Regions/World list/Production Quantity (pick lists)”. UN Food and Agriculture Organization, Corporate Statistical Database (FAOSTAT). 2019.
2. Unknown Author. “Walnut Cultivar Table”. Fruit and Nut Information Center, Department of Plant Sciences, University of California, Davis. 2018.
