If you have the equipment, pressure canning sweet potatoes (or yams) is a fairly easy task. Whether you have a bumper crop from your garden, or buy them cheap at the grocery of farmer's market, you can extend their storage life by canning them.
If you plan on storing fresh sweet potatoes, you should know that they keep very well in cool storage. The bigger they are, the longer they will keep. Large sweet potatoes stored in cool and darkness will keep well over a year. Smaller ones will lose their moisture in storage much more quickly, so won't keep nearly as long.
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When I harvest sweet potatoes from my garden, they come in all sizes, so to prevent them from going bad, I'll can the smaller ones for use later, and eat the bigger ones first. Harvesting will inevitably result in a few damaged but edible potatoes as well. Those sweet potatoes that have stab wounds from the potato fork, are broken in half, or damaged in some other manner are more susceptible to drying out or even rotting in storage, so they will also get canned.
Start by washing off any garden residue from your sweet potatoes. remove roots, soil, etc.
Then, using a potato peeler, remove the skin and cut away any bad places.
Sweet potatoes will turn brown if exposed to the air for long. This doesn't affect their flavor, but it does make them look less appealing. You can avoid this by placing peeled potatoes in water. Warm (nearly hot) water is best, because this will also start warming them up for canning.
Right about this point, you should put on a large pan of water and begin bringing it to a boil.
Once all sweet potatoes are peeled, they need to be cut up to fit in the canning jars. I like to cut them into 1/4 to 1/2 inch thick slices. You can cut them up into what ever size you want as long as they fit into the canning jars.
As you cut them up, return the pieces to the warm water bath to keep them from turning brown.
Fill your canning jars with the cut up sweet potatoes, shake them down to help pack them in. They will shrink some during canning, so pack them tight.
Add 1 teaspoon of canning salt to quarts or 1/2 teaspoon to pints.
Fill canning jars with boiling water, leaving 1 inch headspace.
Finally - apply rings and lids. Screw them down hand tight.
Place closed canning jars of sweet potatoes in the pressure canner as soon as the water is near boiling.
My Presto 23 quart pressure canner will hold 7 quarts (single stacked) or 18 pints (double stacked) at a time.
It's a good idea to know in advance how many pints
or quarts your canner will hold, so you'll know about how many sweet
potatoes to prepare for a "batch".
Process at 10 PSI - quarts for 90 minutes, pints for 70 minutes.
Once done, and pressure has fallen off naturally, remove jars from the canner and allow them to cool to room temperature.
Canning jars may leak some liquid during canning. Since sweet potatoes are so high in sugar, the jars may be sticky after they are removed from the canner, so you may have to wipe down the outside of the jars and lids before storing them.
Canned Sweet Potatoes can be used in most ways you would use fresh ones. Only difference is that they're quicker to prepare.
One of my favorite ways to prepare sweet potatoes is to slice them about 1/4 to 1/2 inch thick and place them in a no stick skillet, cover them with milk, add 4 or 5 tabelspoons of sugar, and a little salt to taste. Heat to a simmer and cook untl the potatoes are soft and the milk/sugar mixture has thickened and reduced by about 1/3 to 1/2. If you use canned sweet potatoes, make the milk and sugar mixture first, then add drained sweet potatoes to the skillet just long enough to get them coated with the milk and to heat them up.
Sweet potato pie can also be made using canned sweet potatoes, since you would have to cook and mash fresh sweet potatoes anyway.
Canning sweet potatoes is an effective way to preserve them for long term storage. Prepared this way, they can be stored and used for several years. Remember - Your garden may not be as productive next year, so take advantage of bumper crops when they come. It's just one more skill in your arsenal for self sufficiency.