Home Food Preservation

Jane Grimsbo Jewett
Minnesota Institute for Sustainable Agriculture, University of Minnesota (www.misa.umn.edu)

Preserving fresh vegetables and fruits at home is a great way to save money and create a healthy diet for your family. Good quality fruits and vegetables, canned or frozen shortly after picking, retain nutrients and good flavor. In fact, they may contain more nutrients than a similar “fresh” food that has spent weeks in warehouses. Nutrient loss begins as soon as a fruit or vegetable is picked. Peeling and cutting, heating, exposure to air and light, and time spent in storage all contribute to loss of nutrients. Refrigeration slows nutrient loss but does not stop it. University of Minnesota Extension estimates that the canning process for green beans causes the loss of about half of the vitamin C in the beans. Canning may still give you a more nutritious product than “fresh” green beans that were picked a week ago and have spent some time at room temperature. Those canned green beans, if stored properly, will lose as little as 5% per year of vitamin C after they have been canned.

Reference: Shafer, William T. 1996. Safe Home Canning of Fruits, Vegetables, and Meats and University of Minnesota Extension.

Which foods should you can, and which should you freeze? This choice is your personal preference, but here are some suggestions:

  • Freeze: berries, rhubarb, sliced apples, tomatoes, squash, pumpkin, sweet corn, summer squash, spinach or other greens, peas, peppers, cauliflower, broccoli
  • Can: pickles, salsa, jam and jelly, tomato juice and sauce, applesauce, green beans, beets, carrots, sauerkraut

The suggested items for canning return a good quality product and let you save freezer space for items that don’t can well. If you prefer frozen green beans and freezer jam, though, that is also fine. Mashed squash and pumpkin should not be canned, because it is impossible to prevent air pockets from forming and causing spoilage. Vegetables other than tomatoes require pressure canning for food safety. For the vegetables in the “freeze” list, the pressure canning time required is so long (70 minutes for spinach, 55 minutes for corn!), that nutrients are destroyed and the final product is not that great. Vegetables on the “can” list have shorter required canning times of 20 to 30 minutes for pint jars, and hold up well through the canning process.

How to Freeze

Use plastic resealable freezer bags of any brand. Freezer bags are thicker than regular food storage bags. For best keeping quality you want to remove as much air as possible from the container. Re-usable rigid plastic containers are fine if you have a liquid or semi-liquid product such as mashed berries or mashed pumpkin. With a lumpy, bumpy product like whole berries or cauliflower, use freezer bags as it is impossible to remove the air from around these foods in a rigid container.

Squeeze as much air as you can out of the bag before sealing the bag. There are vacuum-sealer units on the market that do this or use the following method: fill a deep pan or a sink full of water. Fill a plastic freezer bag with your fruit or vegetable; then put the bag in the water almost-but-not-quite up to the top of the bag. The water pressure forces air out of the bag. Squeeze the bag gently if needed to bring air bubbles up to the surface. Without taking the bag out of the water, close it up: either by “zipping” shut the zipper-type bags, or twisting the top closed of bags with a twist-tie closure. Now take the sealed bag out of the water and dry it off with a towel before putting it in your freezer.

Basic Canning Instructions

Water Bath Canning

Beginning canners should use a water bath canner and stick to pickles, salsa, jam and jelly, fruits, and tomato products. All of these can be safely canned in a water bath because they are “high acid” foods. “Low acid” foods (all vegetables except tomatoes) need to be pressure-canned to kill the spores that cause botulism.

Water bath canning requires a canner; jar tongs; jar funnel; ladle; glass Mason-style jars in quart, pint, or half-pint sizes; jar lids and bands; and a couple ordinary pots and pans. All of these basics can be found at most hardware stores. The two common brands of jars and jar lids are Ball and Kerr. Ball lids work on Kerr jars, and vice versa.

  • Do not re-use lids. The failure rate is high for used lids, and new ones only cost about 13 cents per lid. Honor the time you invest in canning by buying new lids.
  • You should acquire either the University of Minnesota Extension publication: “Safe Home Canning of Fruits, Vegetables, and Meats”; or the Ball Blue Book Guide to Preserving; or both; and have those in your kitchen as references while you are canning.
  • If you are making pickles or salsa, follow an Extension recipe. These have been tested to assure high enough acid content for food safety. You can find recipes on the University of Minnesota Extension Food Safety website.
  • If you are canning tomato products, you should add two tablespoons of lemon juice per quart of tomato product. Modern tomato varieties are bred to be low in acid, so adding the lemon juice will acidify the product to make it safe from botulism when you are using a water-bath canner.
  • If you are making a cooked jam or jelly, seal the filled jars in a water bath canner. This gives you excellent keeping quality. Sealing jars with paraffin wax is an old method that often fails and leads to spoilage of the product.

Food item

Freezing instructions

Using the food

Berries Pick out any leaves and stems; wash berries and pack into plastic freezer bags. Seal the bags, label, and put them in the freezer. You can also put a thin layer of berries on a cookie sheet and freeze them before putting them into bags. This technique keeps the frozen berries from sticking together. Toss a few berries into your breakfast cereal, put them on ice cream, or use in muffins or fruit salad.
Apples Peel apples, cut in quarters, and remove cores from apples. Slice apples into a bowl of cold water with one tablespoon of vinegar or lemon juice or one teaspoon of ascorbic acid per gallon of water (this keeps the apple slices from turning brown). Drain the slices. Pack into plastic freezer bags, measuring the amount per bag that you will need for your favorite apple recipes. Seal the bags, label, and freeze. Use for apple pie, crisp, or cobbler. Do not thaw completely before using; just put the frozen slices right into the pie crust or crisp and bake.
Rhubarb Remove leaves, wash stalks, cut up into bite-sized pieces, pack into plastic freezer bags, seal bags, label, and freeze. Use for rhubarb cake or pie, or make a cooked rhubarb sauce.
Tomatoes Blanch the tomatoes in boiling water to make it easy to remove skins. Heat a large pot of water to boiling, and drop in four or five tomatoes for one minute. Use a slotted spoon or a ladle to remove the tomatoes from the pot, and put them in a bowl or sink full of cold water. This loosens the skins and makes them easy to slip off. Repeat the blanching process until you run out of tomatoes, changing your blanching water occasionally if you are doing a lot of tomatoes. Cut the tough stem ends out of the peeled tomatoes, cut tomatoes in chunks if desired, and pack into containers or freezer bags. Seal, label, and freeze. Use frozen tomatoes for chili, spaghetti sauce, soup, or stew.
Squash or Pumpkin No need to peel these prior to cooking-just cut in half, scoop out seeds and membrane, and bake them at 350 oF for about an hour or until tender. Cover with aluminum foil while baking to prevent drying out. Let them cool; then scoop the flesh out of the rinds with a metal spoon. You can run the flesh through a strainer if you want, but it isn’t necessary. Pack cooked squash or pumpkin into containers or freezer bags, seal, label, and freeze. Heat up squash with butter, salt, and pepper for a side dish with any meal; use pumpkin or squash for muffins, cake, and pie.
Sweet Corn off the cob Corn can be frozen on the cob, but it picks up a “cobby” taste in the freezer, so you get a better quality product if you cut the kernels off the cob. Boil a large pot of water and shuck (peel) the ears. Drop four or five ears in the pot and time for four and one-half minutes. Remove the ears to a pan or sink of cold water (tongs are invaluable for this). Repeat the process until you run out of corn. Keep the cold-water bath cold by running more cold water or adding ice; this cools the cobs quickly to stop the cooking process so that your kernels won’t be overcooked. On a cutting board, stand a cob on end and slice off kernels from tip to base with a sharp knife. You need to make four or five vertical cuts per cob to get all of the kernels. Pack the cut kernels into freezer bags; plan about one third cup of kernels per family member for a meal. Seal bags, label, and freeze. Use corn as a vegetable at any meal. Thaw the bag just enough to slip the frozen corn out, then put the frozen corn in a pan with a little water and heat to simmering, breaking the frozen chunks apart with a fork as it begins to thaw. After corn is completely thawed, simmer for a couple more minutes to complete cooking and heat thoroughly.
Other vegetables Almost any vegetable can be frozen using a blanching-then-cooling technique similar to that for corn. Blanching in boiling water followed by rapid cooling in cold water is very important for getting a good quality frozen vegetable. Blanching stops the enzymes that cause ripening, so that the vegetable stays in its just-picked condition. Rapid cooling stops the cooking process so that the vegetable isn’t overcooked. Blanching times have been tested for each vegetable to hit that “sweet spot” where it is cooked just enough to stop the enzymes, but not so much that it will be overcooked. Find blanching time charts and detailed instructions in the University of Minnesota Extension publication “Freezing Fruits and Vegetables;” online: www.extension.umn.edu/distribution/nutrition/DJ0555.html; or in the Ball Blue Book Guide to Preserving, available at stores where canning equipment is sold or can be ordered online. As with corn, thaw the bag just enough to slip the frozen vegetables out. You may add the frozen vegetable directly to a simmering soup, stew, or stir-fry. Or, place the frozen vegetable in a pan with a little water and heat to simmering, breaking any frozen chunks apart with a fork. Continue simmering long enough to complete cooking.

Water-bath Canning

The basic steps:

  1. Wash and sterilize jars. Extension recommends filling the jars with water, placing them right side up in a large pot full of water, and boiling them for ten minutes. I have personally found it very difficult to then empty the boiling water from these jars without burning myself, so I use an alternate system : fill a shallow pan with about one inch of water, set the jars upside down in the pan with necks in the water, and boil for ten minutes. Steam rises up inside the jars, and steam is hotter than water, so the jars are properly sterilized. Then pull the hot jars out with the jar tongs and set them on a clean towel on countertop or table.
  2. Fill jars. Place a jar funnel in the neck of the jar, and ladle your food product into the jar. Stop filling when you get to the bottom of the neck of the jar, so that you have about ½ inch of “head space” in the jar.
  3. Wipe off jar rims. This is very important—any speck of salt or food on the rim will prevent a good seal.
  4. Add lids and bands. Have these in a pan of very hot water. Use a magnetic “wand” or a fork to pull lids out of the water, being careful not to burn your fingers. Place lids on clean jar rims. Place bands over lids, and tighten the bands by screwing them down. Don’t tighten too much, though. Turn until you first feel resistance, and then give them about one more quarter-turn.
  5. Using the jar tongs, place filled jars in a canner full of hot water. When all the jars are in, the water level should come about one inch above the tops of the jars. Add or remove hot water if necessary.
  6. Bring the canner to a boil over high heat. Pay attention to when the canner is truly boiling; at first you get some air bubbles escaping from under the jar lids, but a true boil will bring up bubbles from deeper down in the pot. Refer to your reference charts for the processing time for your food item. Start timing when the canner starts boiling.
  7. You can turn down heat to reach a slow, gentle boil; but the canner should never stop boiling for the required time. When time is up, immediately remove the jars from the pot with the jar tongs, and place them on a clean towel on countertop or table. Leave a little space between jars if possible; this will speed cooling.
  8. As jars cool, listen for the metallic “pop” that indicates that a jar has sealed. As the jar contents cool and shrink, a vacuum is created inside the jar. This pulls down the little bubble in the center of the lid, causing the “pop.”
  9. Let jars cool for 24 hours. Then remove the bands. This is important—the little bit of moisture left between the jar and the bands will cause the bands to rust, and make it difficult or impossible to open the jars. If the jar lids are properly sealed, you can remove the bands and the lids will stay tight on the jars until you pry them off with a can opener or knife.
  10. Store your jars in a cool, dry, dark place for best keeping quality.

Pressure Canning

Pressure canning is required for low-acid foods. A pressure canner will bring food to a temperature of 240 °F, which will kill botulism spores. There are two main types of pressure canners: those with a dial gauge, and those with a weighted gauge. Weighted gauge canners are more foolproof. A dial gauge needs to be tested every year. A few county Extension offices in Minnesota do this. If yours is not one of them, you can mail the gauge to the Presto canner manufacturer in Eau Claire, Wisconsin for testing. The testing is free, but you have to pay shipping. (National Presto Industries, 3925 N Hastings Way, Eau Claire, WI 54703.)

The basic steps:

  1. Wash jars. No need to sterilize; the pressure canning process will take care of that.
  2. Fill and close jars following steps 2 through 4 under “water bath canning.” With pressure canning you have the option of doing “hot pack” or “raw pack” of vegetables. With “hot pack,” you cook the vegetables first and ladle hot vegetables and water into the jar. With “raw pack,” you put the raw vegetables into the jar and then add hot water to cover them. If using raw pack, leave one inch of head space in the jar rather than ½ inch. Raw pack also requires a few extra minutes of processing time; refer to the time and temperature charts in your Extension or Ball Blue Book references.
  3. The pressure canner should come with a rack that sits in the bottom of the canner. Set jars on this rack. Fill the canner with jars so that they are tight together and cannot rattle against each other and break. If you do not have enough food product for a full canner load, add some jars of just water to take up the extra space.
  4. Add water to the canner so that the jars sit in about two inches of water. You do not want to cover jars with water in a pressure canner. You want the jars in the canner to be surrounded by hot, pressurized steam to raise the temperature to 240 °F.
  5. Wash the rubber gasket for the canner’s lid in hot, soapy water to ensure there is no dust or lint on it. Fit the gasket into the lid, and lock the lid in place on the top of the canner. If using a weighted gauge, do not put the gauge on the canner yet. If using a dial gauge, leave the vent open.
  6. Bring the canner to a boil over high heat. When steam begins venting out of the top, begin timing for ten minutes. After ten minutes, close the vent on a dial-gauge canner or put the gauge on a weighted-gauge canner. This steam venting step is very important; it expels all of the air from the canner so that the inside is completely filled with hot steam. This ensures that there won’t be any “cold spots” in the canner that do not reach 240 °F.
  7. Bring the canner up to pressure over high heat. With a dial gauge, watch the dial until it reaches the pressure required for your food product. With a weighted gauge, listen for the gauge to “chatter” as it begins to release a little steam from the canner. Once you have the canner pressure at the correct level, begin timing according to the charts in your reference materials.
  8. Adjust stove heat to maintain the required pressure. A dial gauge should stay right at the required pounds of pressure. A weighted gauge should “chatter” twice per minute, with a few seconds’ pause between chatters.
  9. When time is up, remove the canner from the heat. Then just let it sit to cool down gradually. Do not do rapid cooling by running cold water over the canner; this will cause your glass jars to cool too fast and they may break. Do not remove the weighted gauge or open the vent until the canner is cool. Once it is cool enough to hold your hand on it, you can open the canner and remove the jars.
  10. Continue with steps 8 through 10 under “water-bath canning.”

Cool Storage

The easiest food preservation activity, if you are lucky enough to have a cool but not freezing storage spot, is to store some sturdy fruits and vegetables in that space. If you have a chilly corner in a basement, or an entryway, or an upstairs closet, you have a potential food storage location.

Onions and garlic are good vegetables to store in a cool, dry area. Hang a mesh bag or braided rope of onions or garlic from a hook in a cool closet or entryway. Potatoes and apples store well in cool, moist air, such as in a basement. Around 40 °F is ideal, but they will keep for a couple of months at 50 °F.

Carrots, parsnips, beets, turnips, and rutabagas dug in September or October will keep for a couple of months in an unsealed plastic bag in your refrigerator. If you have an unfinished section of your basement that is chilly (under 40 °F), you can keep these kinds of root vegetables there in boxes or bags for several months. Use several smaller containers instead of one large container. That way, if you have some spoilage in one container, it won’t affect all of your stored vegetables.

With any kind of cool storage of apples or root vegetables, look over your stored food fairly often. Throw out anything that is starting to spoil. If you really want to get into this type of food storage, the book Root Cellaring: Natural Cold Storage of Fruits and Vegetables, by Mike and Nancy Bubel, Storey Publishing, 1991 is a superb reference.

Other Methods of Food Preservation

The National Center for Home Food Preservation at the University of Georgia has a clearinghouse of information on every food preservation technique. In addition to freezing and canning, you can find recipes for pickling, fermenting, curing and smoking, and drying of foods.

Portions of this article were first printed in “Local Food: Where to Find It, How to Buy It,” a publication of the Minnesota Institute for Sustainable Agriculture.

Read Up

Root Cellaring: Natural Cold Storage of Fruits and Vegetables by Mike and Nancy Bubel. Storey Publishing 1991.

Ball Blue Book Guide to Preserving. Alltrista Consumer Products 2004.

University of Minnesota Extension publication: Safe Home Canning of Fruits Vegetables and Meats. 

Food Preservation

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