Preserving Potatoes

potatoes

Not known for their fragility, potatoes are a robust, starchy tuber in the nightshade family (along with fellow Solanaceae family members tomatoes, eggplants, and peppers). Potatoes pack a nutritional punch, weighing in with substantial amounts of potassium, fiber, protein, vitamin C, Vitamin B-6, Magnesium, and a lesser but still notable amount of Iron.

It’s easy enough to store fresh white potatoes for up to 2 months in a cupboard kept at 50-70°F (sweet potatoes last only 2-3 weeks). But what if you want them to last even longer?

Interestingly, storing white potatoes in a refrigerator is likely to diminish their quality and they are expected to last only 1-2 weeks there. Alternatively, you could cook and mash them, stuff them, or scallop them for freezer storage, but again, they will retain best quality only for a few weeks in the freezer.

Drying is an option for making potatoes last longer. Wash, peel, then cut potatoes into 1/4-inch thick shoestring strips, or cut into 1/8-inch thick slices. Steam blanch the prepared pieces for 6-8 minutes or water blanch them for 5-6 minutes. Plan for a drying time of 8-12 hours in a dehydrator and up to twice as long in an oven, depending on circulation. If you dry sweet potatoes and want to rehydrate them for a recipe, combine each cup of dried pieces with 1-1/2 cups water and let them soak for 30 minutes.

As for canning potatoes, our recommendation is to peel potatoes before canning. That style of preparation is how the research was carried out to determine the recommended processing, and in order to know that the peeling does or does not make a difference, research would need to be done with unpeeled potatoes. Different assumptions might be needed in assessing just how many spores of C. botulinum or other bacteria might be present at the start of the process and what amount of heat might be needed to meet standards for the risk of possible survivors. We do not know of research of canning potatoes with peels left on, so we recommend the preparation steps provided with the process recommendation, especially because there is a possibility that the deviation could result in a less safe situation. Also due to safety concerns, it is important to use potatoes that are only 1 to 2 inches in diameter if you are canning them whole.  These are sometimes described as “new” potatoes; the idea is to use less mature, smaller potatoes which tend to be less starchy than older, “grown-up” potatoes.

White potatoes for canning should be the “waxy” or “boiling” kind.  Different types of potatoes have different amounts and types of starches and they react to heating differently.  You want a potato that keeps its shape and texture well after a lot of heating, and not one that falls apart, becomes “fluffy” after cooking, and is better for mashing. Most red-skin potatoes are of lower starch than baking potatoes  and work well for canning. Many white round potatoes with thin skins fall into this category with red-skin potatoes too. Russets are not good for canning but are  good for baking (they have a high starch content).  Yukon Gold may not be the best potatoes for canning.  While they seem good for boiling, they do tend to fall apart when overcooked.  From what we have read, there is a wide variety in the types and amounts of starches in blue potatoes, so not all blues are the same, just like not all white potatoes are the same in these characteristics.

Sweet potatoes can be slightly larger, but medium-sized potatoes should be cut to fit in the jar in uniform-sized pieces. Note that the sweet potato pressure canning process time is significantly longer than for white potatoes.

Sweet potatoes can have a sugar syrup for canning, if you like that style. But otherwise, all potatoes — white or sweet — should have fresh, boiling water prepared to pour over the preheated potatoes.  Do not use the cooking liquid.  That cooking water contains a lot of starch that comes out of the potatoes and the process time was determined using fresh boiling water to cover.  The added starch can create  a safety problem by slowing down heating of the potatoes in the canner, and it also creates a very unappealing pack with possible masses of gelled or congealed starches around the potatoes.  If you have spoilage, this makes it very hard to see the signs of some spoilage.

Advertisements

5 thoughts on “Preserving Potatoes

  1. Sheila

    While we’re on the subject of carrots, is it safe to can “baby-cut” carrots which I understand have been chemically peeled using lye?

    1. nchfp Post author

      First of all, apologies for the long delay in our response. We will try to be very thorough to make it worth your wait!

      To our knowledge, no testing has been done for canning low-acid baby carrots versus regular full, size carrots. Our canning recommendations for carrots were developed using full size, 1 to 1-1/4 inches in diameter, carrots. (See http://nchfp.uga.edu/how/can_04/carrots_sliced.html ). We are not aware of any risk from using manufactured baby carrots, but again, we are not aware of studies specifically examining their use for home canning either.

      We have created a pickled baby carrot procedure for canning in our lab, using store-bought, already peeled baby carrots. We did not notice a discernible difference in raw pH over raw large, peeled carrots, but we were not specifically trying to make those comparisons, either. (In other words, the pH of the store-bought baby carrots was well within the expected range of regular raw carrots.) If you are pickling baby carrots, even though we only used one source and brand, our pickling procedure for others should offer adequate safety margin:
      http://nchfp.uga.edu/how/can_06/pickled_baby_carrots.html

      Not all “baby carrots” are even manufactured the same. Some are cut from larger carrots, some are harvested very young, tiny carrots. To our knowledge, many or even most are skinned by mechanical peelers and polishers; we cannot confirm or find the use of lye peeling in this process and certainly not for all brands. There may be a very dilute (weak) chlorine solution used in the manufacture of some to extend the shelf life (it has an antimicrobial effect). Liquid “chlorine” is usually a solution of sodium hypchlorite and can be manufactured by reacting lye with the elemental chlorine gas. That doesn’t mean the carrots are exposed to lye itself, and chlorine is an approved antimicrobial treatment for the cut vegetable. It gets rinsed off after exposure of the carrots. Organic manufacturers (or others) have alternative antimicrobials to use over chlorine.

      If manufactured baby carrots are in fact treated directly with lye, the safety risk would be determined by how much the lye raised the pH over the natural carrot. And we cannot answer that; a particular manufacturer may be willing to tell you if they even use lye peeling as a start.

      The USDA directions for canning carrots used, and assumes, people are wanting to can fresh carrots and follow the directions for prepping them as given in the canning procedure (the first link above). Those are our recommendations for canning carrots at home, in addition to the pickled products (including relishes with carrots) we offer.

      Another related note: some people claim the whitish appearance is chlorine coming to the surface; perhaps others think it is lye since you are hearing somewhere that lye is used. In reality, the pieces will dehydrate over time and the whitish blush outside is from the dry carrot tissue appearance.

  2. Randal Oulton

    I’m curious, do you reckon that’s why directions for pressure canning carrots call for them to be peeled first — there’s no research yet on unpeeled ones? (I don’t usually peel carrots otherwise, as so much fibre and nutrition is in the peel, and during the war in England you weren’t allowed to peel carrots because of the food wastage!)

    1. nchfp Post author

      Although we do not know all of the exact reasoning from USDA when the canning process was developed for carrots to be peeled, it is true that we only recommend canning procedures as they were developed during laboratory testing. One important difference to canning between peeled and unpeeled carrots is the potential difference between bacterial loads going into the canner. In other words, removing the peel from carrots substantially reduces the amount of bacteria on the carrots. Carrots with peel left on, even if washed well, would likely contain more microorganisms when compared to peeled carrots. Before recommending canning carrots with peels left on, we would need to see product development testing that accounted for the increased microbial load and any other possible changes with peel included in the jars. Although you don’t see much reduction in fiber after canning, you will still lose some of the nutritional value in the peel that comes with heating and sitting in water, just as you do with the flesh of the peeled carrot. There is no nutritional analysis or comparison available for carrots canned with or without peels, especially since carrots canned commercially do not contain the peel, and those are the source of most of our nutritional values for canned foods.

      As for all those carrot peels, well, at least at home the peels could be turned into excellent compost!

      1. Randal Oulton

        That’s what I reckoned, “germs” on the skin, untested. And the other reason for just double-checking was that I’m lazy, I hate peeling :} But thanks for the info, I will keep on peeling — or conning other people into the task :} I appreciate your time greatly the background information was very useful.

Comments are closed.