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Flaxseed is most often sold in vacuum-sealed bags or refrigerated pouches. One of these containers will work just fine for short-term storage, especially if you tend to go through the superfood in a hurry. Just zip or roll up the bag or pouch, slip a rubber band around it, and stick it in the refrigerator. Keep your flaxseed on a central shelf so it will be in your line of sight when you open the fridge. That way, you won’t be as likely to forget about it. Glass jars are by far the best storage method for oily grains like flaxseed. Not only do their canning lids lock down to form an airtight seal, they can also be washed and reused an infinite number of times. The fact that they’re transparent means it’s easier to identify what’s in the jar and see how much you have left at a glance, too.  Don’t forget to label your mason jars with the contents and expiration date. Glass in a nonreactive substance, so you won’t have to worry about the valuable nutrients in the flaxseed breaking down before their time. Standard plastic storage containers are a fine choice for flaxseed that you’re planning on using within a couple months. They’re available in a variety of sizes, and you can almost always dig a spare out of the back of a cabinet or the bottom of a drawer. For freshness, look for containers with lids that seal tightly. Stay away from plastics containing BPAs. It’s possible for these harmful chemicals to leach into foods that have been in storage for a while. If you don’t have a more durable container on hand, a plastic bag will do. Funnel the flaxseed into the bag carefully to avoid spilling it and press out as much air as you can before sealing. Make sure the zip closure is snapped tight all the way across.  One advantage of plastic bags is that they come in multiple sizes, which makes them useful for storing leftovers, meal prepping, and packing lunches. Plastic bags are more likely to break or allow air in, so they shouldn’t be used for storing sensitive grains like flaxseed for long periods. Dark containers, like green glass and tinted or opaque Tupperware, admit less light, which is one of fresh flaxseed’s worst enemies. As such, they’ll provide longer-lasting results than transparent containers kept under the same conditions. Avoid leaving flaxseed in brightly-lit areas, such as on the countertop in the path of the setting sun, when storing it at room temperature. When whole flaxseed is reduced to small pieces, its fatty acids begin to break down rapidly, which can cause it to spoil in as little as a week when stored at room temperature. Make sure your grains go straight into a sealed jar or piece of Tupperware after they've been processed. This will help extend their shelf life to its maximum potential.  Double check that the lid is nice and secure, and try not to open the container unless it's to portion out a scoop. Try to use up your ground flaxseed as soon as possible in order to take advantage of its full flavor and nutritional value. You may be able to stretch your ground flaxseed for as long as 2-3 months by finding room for it in the refrigerator.

Summary:
Leave flaxseed in its original packaging for 6-12 months. Transfer opened flaxseed to a glass mason jar. Stash your flaxseed in an airtight lidded container for 4-6 months. Keep pre-portioned flaxseed in a plastic zipper bag for 1-2 weeks. Opt for dark containers over clear ones. Move freshly-ground flaxseed to an airtight container for 3-4 days.