Answers to Common Canning Questions
- Can I use my own recipes when I can foods like salsa and soups?
- If my recipe does not call for processing the food, do I need to process it anyway?
- Do I need to sterilize jars before canning?
- Can I reuse jars, lids, and bands?
- Why did my jars break in the canner?
- Why did my jars of food lose liquid?
- Why is the liquid in the jars cloudy?
- Why did the food I canned change color?
- How do I test jars to make sure they are sealed correctly?
- Can I reprocess food if the lid did not seal?
- There is mold growing in the jars of food I canned. Can I scrape it off and eat the food?
- Why did my home-canned food spoil?
- How long can I keep home-canned food?
- You must use only up-to-date recipes (published in 1990 or after) that have been scientifically tested to be sure that all harmful microorganisms will be destroyed during the canning process.
Microorganisms are found naturally on fresh foods. Many cause foods to spoil, but some cause foodborne illness. When you are canning, do not change any ingredients in the recipes and follow the directions carefully. You can find scientifically tested recipes in reliable sources. We recommend the USDA Complete Guide to Home Canning and the National Center for Home Food Preservation.
*If you cannot find a recipe for the food you want to can, consider freezing the food as that is a safe alternative.
- Yes, do not rely on old canning recipes that do not call for processing or those that
call for processing in an oven, steam canner or open kettle. You must use canning
procedures that will keep the food safe.
- When canning high-acid foods, such as fruits, pickles, jellies and jams, you can process them in a boiling water bath canner.
- When canning low-acid vegetables (e.g., corn and beans), meats, fish and poultry, you must process them in a pressure canner. The bacterium Clostridium botulinum can grow in improperly canned low-acid foods. This bacterium causes botulism, a deadly form of foodborne illness, so be sure to use the correct canning method for the food you want to can.
You do not need to sterilize jars if they will be processed in a pressure canner or if they will be processed in a boiling water bath canner for at least 10 minutes. If the jars are processed in a boiling water bath canner for less than 10 minutes, you will need to sterilize them first by boiling in hot water for 10 minutes before you fill them with food.
- Do NOT reuse jars with nicks, cracks or chips, especially around the top sealing edge, as these jars will break under pressure and heat.
- Only use jars with two-piece, self-sealing metal lids.
- Do NOT reuse the lids as they will not form a tight vacuum seal.
- Screw bands are reusable only if they are not bent, dented or rusted.
*At the beginning of each canning season, check the jars, lids and bands that you have to determine what to buy.
Jars can break for several reasons:
- if you use commercial jars that are not manufactured for home canning
- if your jars have cracks and chips
- if you put jars directly on the bottom of a canner instead of on a rack or if you put hot food into the jars when they are cold
- if they contain raw or unheated food and you place them directly into boiling water in the canner
*Regular and wide-mouth Mason-type, threaded, home canning jars with self-sealing lids are recommended, and they can be reused many times if handled carefully.
Jars can lose liquid for several reasons:
- if you did not cover them with 1 to 2 inches of water in the canner
- if you packed the food in the jars too tightly
- if you do not work out air bubbles from the jars before processing
- if you are using starchy foods (sometimes they will absorb more of the liquid during the canning process)
* Loss of liquid is not a sign of spoilage, but do NOT open the jars and add liquid because that will cause the food to spoil. If you lost half the liquid or more, refrigerate the jars and eat the food within two to three days.
- A cloudy liquid could indicate that the food is spoiled, so recheck your canning recipe to be sure that it is from a current and reliable source and that you followed the recommended processing method, time and temperature.
- Sometimes a cloudy liquid comes from starch in overmature, starchy vegetables (e.g., corn) or from minerals present in soft water.
- Fillers (anti-caking agents) in table salt also can cause clouding, so use pure refined salt when possible.
- Enzymes can cause food near the top of the jar to turn a dark color. You may not have processed the food long enough to inactivate the enzymes, so recheck your recipe.
- Dark color near the top will occur if you did not use enough liquid or syrup to cover the food or if you did not remove air bubbles before sealing the jar.
- Sugar in corn will caramelize, and corn will turn brown if processed at a temperature that was too high.
- Minerals, such as iron, zinc, and copper, in cooking utensils or water can cause various color changes in food.
- Immature and overmature produce can change color during the canning process too.
After cooling jars for 12 to 24 hours, remove the screw bands and test seals in one of the following ways:
- Press the middle of the lid with a finger. If the lid springs up when you release your finger, the lid is not sealed.
- Tap the lid with the bottom of a teaspoon and if it makes a dull sound, the lid is not sealed. If food is in contact with the underside of the lid, it will cause a dull sound too. If the jar is sealed correctly, it will make a ringing, highpitched sound. Finally, hold the jar at eye level and look across the lid. If the lid is concave (curved down slightly in the center), it is sealed, but if it is either flat or bulging, it is not sealed.
Read more about testing jar seals.
Yes, BUT only if you detect it within 24 hours of the time you processed it.
*If it has been longer than 24 hours since you first processed it, the food will NOT be safe to eat, so throw it out.
Start by removing the lid and checking the jar sealing surface for any nicks. Change jars in the case of nicks, and then add a new treated lid. Reprocess it using the same processing time that you used initially.
Reasons for jars not sealing include:
- nicks and cracks in jars
- failure to follow lid manufacturer’s directions for closing
- using rusty bands
- reusing self-sealing metal lids
- leaving food particles or fat from food on jar rims
- insufficient headspace in the jars
*Always be sure to wipe rims with a clean, damp cloth before closing to prevent seal failures.
Do NOT eat home-canned food that has mold growing on it. Throw it out!
Mold can change the acidity of the food, making it less acidic. Bacteria are more likely to grow in low-acid foods, especially the very harmful Clostridium botulinum bacterium that causes botulism. If there is ANY mold, or signs of other spoilage, discard the entire contents of the jar or container, even jams and jellies.
A number of things can cause home-canned food to spoil.
- To prevent spoilage, start with the best quality food and then process it quickly and correctly, because bruised and insect-damaged food contains microorganisms that cause spoilage.
- Use canning recipes from current and reliable sources, and follow the recommended processing methods, times and temperatures.
- Do not overfill jars, and do not change ingredients in a recipe because it has been scientifically tested for safety and quality.
- Use supplies and equipment that are in good working order, or have them repaired or replaced before you start to can.
*Agents are able to test gasket-style canners with a dial gauge for free. It is recommended that the pressure canner gauge is tested each year prior to canning season. Contact your local extension agent to set up an appointment.
Read more about identifying and handling spoiled canned food.
You will need to use it within a year because the quality will deteriorate. Food safety experts recommend that you do not use most home-canned foods after one year. All home-canned foods should be stored in a cool, dark, dry place, between 50-70°F.
Over extended periods of time, however, changes in color, flavor, texture and nutrient content of home-canned jams and jellies is inevitable. A typical full-sugar fruit jam or jelly should be safe to eat if the jar seal remains intact and the product shows no visible signs of spoilage from molds or yeasts.
Jams and Jellies
Some jams and jellies may have a shorter shelf life than others for optimum quality. For example, lighter-colored jams and jellies may noticeably darken faster than others and not remain appealing for a whole year. Though this is not a safety concern, it may reduce the visual appeal of the product for many people. The type of fruit used will also affect other quality characteristics over time.
Reduced sugar jams and jellies may deteriorate in color and texture more quickly as they lack the full preservative effects of the sugar. Some fruits may darken more quickly with less sugar present. Flavor changes that occur over time become more evident if they are usually otherwise masked by the sugar.
Freezer/refrigerator jams and jellies are a distinct category of products that have to be stored in the refrigerator (usually up to 3 weeks) or frozen for up to a year.
It is always a good practice to carefully examine all home-canned jars of food for signs of spoilage prior to opening and eating. If there is any mold on a jar of jam or jelly, or signs of other spoilage, discard the entire contents of the jar or container.
Be sure you have the right storage place.
- If the temperature is too hot, the food will lose its quality.
- If it is too cold, the food will freeze and the jars will burst.
- Dampness will corrode metal lids and break seals causing spoilage, so store food in a cool, dry place at temperatures between 50° and 70° F.
*If you do not have enough storage space for all the food you want to can, freeze some of it as this will help you preserve as much of it as possible.
Still have questions?
Contact your local county Family Consumer Science Agent! Find your county's Extension office.
- Preserving Food: Using Pressure Canners
- Storing Home Canned Foods
- What you Should Know about Preserving Food at Home
- Foodborne Illness: Debunking the Myths