Tag Archives: pressure canning

Preserving 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.

Putting A Lid On Green Beans

IMG_1110Having a green bean emergency?! So many questions came in over this summer about canning green beans that it seems time to discuss what is and is not recommended for the process. No one wants to be told that they under-processed their precious jars of homegrown green beans and need to discard them to be safe, but unfortunately we’ve had to break the news repeatedly.

Let’s first address the most common and critical safety concern with canning green beans: “I canned my green beans using a boiling water bath…is that ok?”

Oftentimes upon the advice from a grandmother or neighbor, people make an attempt to can their green beans using a boiling water canner. BOILING WATER CANNING IS NOT A SAFE OPTION FOR GREEN BEANS. While stories may be told of how they’ve done it for years and never gotten sick, the risk of botulism is ever present in canned green beans that were processed in a boiling water canner. Such beans are under-processed, not having received a heat treatment at a high enough temperature to destroy the toxin-producing spores of Clostridium botulinum. The concern is real: under-processed green beans caused two outbreaks of botulism in the United States in 2008 and 2009.

The only process we support for canning green beans is using a pressure canner. Here are our recommendations for Canning Green Beans. The process itself is simple – wash, snap, boil, fill, process – but the use of a pressure canner is absolutely critical to ensure the safety of the beans. The pH of green beans (5.7 – 6.2) is well above the cut off that can be processed in a boiling water canner (4.6 or below).

IMG_4675If you do not have a pressure canner and do not plan to get one, you do have the delicious option of canning Pickled Dilled Beans in a boiling water canner. This recipe has enough vinegar that the overall pH of the product lowers to the safe zone for boiling water canning – also called acidification, or pickling. Don’t like pickled products? Try freezing your green beans or even drying them into a snappy snack!

Why Can’t I Just Guess at a Process Time for Canning?

Mold on JamIf you guess at a process time for canning, you run the risk of underprocessing your food, which could lead to food poisoning and/or product loss due to spoilage.

All reliable recommendations for canning include process times that have been determined by or based on results of laboratory testing. The exact time and temperature combinations of tested canning processes are needed to assure the destruction of microorganisms that may be present in the filled jars. Sure, it’s possible that you could use unsafe canning practices for some time without causing waste or harm, but it only takes one batch of food with destructive microorganisms in it to ruin your streak of luck. And especially if you are canning low acid foods, the consequences could be severe and irreversible.

While some microorganisms are apparent just by looking (think molds growing on the surface of jelly), others remain invisible to your bare eyes (think pathogenic bacteria which cause food poisoning). Many different types of mold, yeast, and bacteria dwell on food. Given their preferred conditions of moisture, acidity, oxygen levels, and temperature they will grow, and some will even product toxin.

Fortunately, all microorganisms can be destroyed by breaking their threshold for heat. The process times provided in each of our home canning recommendations have been found to deliver enough heat to destroy microorganisms of concern in that particular food. Characteristics such as consistency, pH level (acidity), size of food pieces, presence of protective nutrients, size and shape of jars, and solid to liquid ratio all influence the ability of heat to move through and thoroughly penetrate the entire contents of a filled jar. You can trust that your home-canned foods will receive adequate heat treatment by using proper canning methods and following recommended process times.

Why does each recipe have a process time table with multiple times or amounts of pressure? (See Crushed Tomatoes for a good example.) Because atmospheric pressure decreases as altitude increases, causing water to boil at lower temperatures as altitude increases. In order to achieve the same overall heat treatment as at sea level, more time is needed in a boiling water canner at higher elevations (since the temperature of the water distributing the heat is less). Pressure canning relies on temperatures inside the canner building even higher than that of boiling. So, likewise, more pressure needs to be applied to a pressure canner at higher elevations so that the temperature inside can reach higher.

If you’d like to learn more about how process times are determined for home-canned foods, please read ‘Backgrounder: Heat Processing of Home-canned Foods’ by Elaine M. D’Sa.

Got the Wintertime “Greens”?

frozen lettuce

Chances are that you don’t have much to harvest from your garden these days, but if you do, then there’s a good chance it’s at least somewhat green and leafy. Lettuce, bok choy, spinach, turnip greens, collards, and swiss chard are among the hearty plants that are able to thrive in cooler temperatures. If your local temperatures have been too cold even for those crops, then head to a grocery store and keep your eyes open for special deals and seasonal sales in the produce department. Keep in mind however that lettuce has such a high water content and such thin tissue that it does not tend to preserve well using any method.

As mentioned in the recent New Year’s posting, Spinach and Other Greens can be canned, using a pressure canner. You might be amazed at the quantity you can fit in each jar once the tender leaves have wilted from being steamed – a canner load of 9 pints requires about 18 pounds of greens, and a canner load of 7 quarts holds an impressive average of 28 pounds! Note: These “other greens” should be greens with a similar texture to spinach, and not very hard, firm leaves such as cabbage.

Freezing greens is an option, but is recommended only for use as a cooked vegetable. This is for the sake of quality — their cells are full of water and those thin cell walls will burst when that water freezes and expands. So, rather than making a salad with frozen greens, try using them in casseroles, lasagna, soups, sauces and dips. Also, keep in in mind that leafy greens will heat more evenly if thawed before cooking. The water blanching time for most Greens, including Spinach, is 2 minutes, but water blanch collards for 1 additional minute (blanch time: 3 minutes) and Cabbage for 30 seconds less (blanch time: 1½ minutes). Blanching is important to slow or stop destructive enzyme action, clean surfaces, brighten color, help retain vitamins, and make the vegetables easier to pack into jars. Specific directions for water blanching are available here.


Perhaps the least common method of preserving greens is to dry them. However, dehydrating can be a useful method for use in baked goods, soups, and casseroles. Dried greens may even be ground into flour to sneak some extra nutrients into breads, pancakes, and cookies. As with freezing, blanching is required. Cabbage can be water blanched for 1½ to 2 minutes or steam blanched for 2½ to 3 minutes or until wilted. Other greens can be water blanched for 1½ minutes or steam blanched for 2 to 2½ minutes or until wilted. Read this publication from the University of Georgia for more information about Drying Fruits and Vegetables.