Between the stories of pressure cooker explosions, cooktop burnout and the risks of spoilage, canning can seem a tricky thing. We searched the web over for answers from experts, manufacturers and scholars that we think put Urban Food Legends in their place.
COOKING SURFACES: First, if you’ve heard you can’t can on a flattop or induction range, it really depends upon the equipment and processes you’re planning to use. It can be done, just maybe not the way you’re used to doing it. Most damage is caused by dismissing manufacturer recommendations for cookware, prolonged burner use or overweighing the cooking surface.
From the extensive archive of the food blog, Food in Jars :
“Many older canners have concave bottoms. When you combine a concave bottom with a flat surface, heat, and water, there is a risk that a seal will form between the canner and the stovetop. You can eliminate the risk of breakage through suction by using a pot with a flat bottom.”
Another blogger at Canning Homemade has this recommendation: “Use a flat bottom canning pot and make sure to measure the largest dimension burner and purchase a canner that is that size or no more than 1" in diameter larger. Always follow the basic information using your particular pot sizes on your glass top from your stoves manual.” One piece that is recommended repeatedly is the “16 qt. Presto Canner which is truly a flat bottom canner. The diameter is 14.8x14.8 which means the flattest portion is the same as the outside.”
Most manufacturers dedicate an entire page of their Use & Care Manual to encourage proper canning techniques for this very reason.
From GE: “A pressure cooker can be used on an induction cooktop. You can also do canning as well. Try the magnet test (a magnet must stick and hold to the bottom of the pan) on any pressure cooker or canner in question. It is also preferable to size the cooker or canner to the size of the burner.”
From Whirlpool: “Canning can be performed on a glass smooth top cooking surface. When canning for long periods, alternate the use of surface cooking areas or elements between batches. This allows time for the most recently used areas to cool. Center the canner on the largest surface cooking area or element. On electric cooktops, canners should not extend more than ½” beyond the surface cooking area of element. Do not place canner on 2 surface cooking areas or elements at the same time. On ceramic glass models, use only flat-bottomed canners to avoid damage tto the cooktop and elements. For more information, contact your local agricultural extension office**, or refer to published home canning guides. Companies that manufacture home canning products can also offer assistance.”
From Frigidaire: “Home Canning Do’s and Don’ts. Use only qualifying flat bottom canners when home canning. Use a straight–edge to check canner bottom. Use only a completely flat bottom canner with no ridges that radiate from the bottom center when home canning. Heat is spread more evenly when the bottom surface is flat. Make sure the diameter of the canner does not exceed 1 inch beyond the surface element markings or burner. It is recommended to use smaller diameter canners on electric coil and ceramic glass cooktops and to center canners on the burner grated. Start with hot tap water to bring water to boil more quickly. Use the highest heat settings when first bringing the water to a boil. Once boiling is achieved, reduce heat to lowest possible setting to maintain that boil. Use tested recipes and follow instructions carefully. Check with your local Cooperative Agricultural Extension service** or manufacturer of glass jars for the latest canning information. It is best to can small amounts and light loads. Do not leave water bath of pressure canners on high heat for an extended amount of time. Alternate surface units between each batch to allow the units and surrounding surfaces to cool down. Try to avoid canning on the same burner unit all day.”
** Our local resource happens to be the UAF Cooperative Extension which has an extensive library of information for food preservation in Alaksa.
To avoid scratching your cooktop when using large, heavy cookware, heed this note from National Center for Home Preserving: “Even if a manufacturer says a burner/cooktop can be used for canning you should be aware that scratching can occur if the aluminum canner is slid or pulled across the cooktop. This often happens with large, heavy filled canners.”
TOOLS: There are also many small but handy tools available to make you and the food your preserving, stay safe.
Using a magnetic lid lifter minimizes contact with hot sterile lids, which keeps them clean and keeps your fingers from being burned by the hot water bath.
A coated metal jar lifter allows you to move hot jars safely into and out of a hot water bath. National Center for Home Food Preservation (http://nchfp.uga.edu) suggests, "When moving jars with a jar lifter, make sure the jar lifter is securely positioned below the neck of the jar (below the ring band of the lid). Keep the jar upright at all times. Tilting the jar could cause food to spill into the sealing area of the lid."
"The bubble tool looks like a staircase and has two main functions; to measure headspace (the unfilled space in a canning jar between the top of the food or liquid and the underside of the lid) and eliminate air pockets that form when filling your jars. The correct amount of headspace is essential to allow for food expansion as the jars are heated and for the formation of a strong vacuum seal as jars cool. You can use this tool by resting the stair on the glass rim of the jar for the measurement required by your recipe and then making sure that your food or liquid just touches the bottom of the last "stair". Remember to remove any air bubbles before you do your final measuring as the level of the food will go down after removing those pockets. If you have a recipe that doesn't have a headspace measurement called out, first it may not be a safe recipe for canning, but it also could have been quickly typed and omitted. The rule of thumb for recipes are:
1/4" headspace for Jams, Jellies, Marmalade, Chuntney, Spreads & Butters
1/2" headpace for Pickles, Tomatoes, Fruit
1" headspace for Vegetables (not pickled)
1" - 1 1/2" headspace for Meat, Poultry, and Fish
I would rather many of you learn how to do this with some kind of measuring device before you start eyeballing which at times may be the reason that your jars do not seal. Too much headspace can make it difficult to drive out all the air during processing and as a result you don't get a ping! Not enough headspace can lead to food pushing up on the lid during processing and getting trapped between the glass and the rubber not allowing it to seal." (From: Canning Homemade)
RECIPES: It may be tempting to omit or substitute ingredients, but to ensure your end product is shelf sage, it's important to stick to a recipe. On a recent Facebook chat Ball Canning Expert, Jessica Piper said, "As long as you follow a tested & approved recipe for safe home food preservation, you should have absolute confidence in yourself! When properly preserved, home canned foods have a shelf life of one year."
General Canning Safety Tips
When you’ve completed your processing, and jars are cooling, you should hear the telltale ‘pop’, indicating your lid has sealed. But who has time to wait around counting pops- although it is a very satisfying sound if you do happen to catch it! So here are some tips for a post-process seal check.
By Ingrid Gadpaille, Kitchen Store Specialist
After the jars have cooled for 12 -24 hours, check the seal of each one with any of the following methods:
Remove the screw bands and:
- Press down in the center of the lid; it should not give at all, this is a proper seal.
- Lift the jar by the lid; hold opposite hand under the jar to catch it if the lid gives! If it doesn’t, it’s properly sealed.
- Lift the jar and look at it at eye level, if it’s curved downwards in the center, it’s sealed properly.
- Tap the center of the lid with the back of a spoon; if it makes a ringing tone, it’s properly sealed. If it makes a dull thudding tone, there may be food at the top of the jar touching the lid – check and see by looking inside at eye level and use one of the other methods to confirm a proper seal.
Mis-sealed jars can be reprocessed. Remove the lid and check the rim of the jar for nicks. If there are nicks, use a new jar and reprocess. The product will not be of the same quality as single process. If you don’t want to reprocess, refrigerate and use within 3 days.
Checking for spoilage
Checking for spoilage is done both before and after the canning process. Make sure that all the food is clean, trimmed and spot free. Once canned and available for use throughout the year, check for spoilage by:
- looking for leaks or streaks on the outside
- rising air bubbles in the liquid
- bad coloring. Very dark content is an indication of spoilage. If the food has some light discoloration it may be from minerals in the water and the contents are still safe. (Do a seal check.)
- contents are slimy, shriveled or cloudy.
- the contents are under pressure and burst out when the jar is opened.
- after the jar is open, look for mold spots that can be blue, green, black or white in color.
- if the contents smell odd or unnatural, it should be discarded.
DO NOT TASTE ANYTHING THAT MAY BE SPOILED!!
Proper disposal of spoiled product
If the jar is still sealed, place it in a garbage bag, wrap it tightly around the jar and dispose of it in the trash.
Note: Low acid foods and tomatoes do not show spoilage in the same way that other foods do. If there is any suspicion of spoilage, dispose of it properly!!
Before gifting, use a label to record what you’ve canned, the date it was sealed and the method used. This will help the receiver know how to properly store and make use of their delicious food gift.