K-State Research and Extension

As with any problems when cooking, there are many reasons to answer a question.  For pressure canning, here are some reasons for the question above:

• Improper headspace to allow for food expansion.
• Pressure canner was not exhausted for 10 minutes before pressurizing.
• Pressure too high.
• Unsteady heat source caused pressure fluctuation.
• Removing pressure regulator before pressure dropped completely.
• Rapid temperature changes or drafts blowing on the canner.
• Lids not applied correctly.
• Raw pack was used instead of hot pack.
• Did not leave canner closed for 10 minutes after pressure dropped completely.

Source: www.gopresto.com and https://nchfp.uga.edu/how/general/cannedfoodproblems.html

Many resources show home canning methods that are not safe. Here are a few:

• Canning in the oven—Canning jars may not withstand the thermal shock and can break. Also, oven heating filled jars of food is slow and can encourage potential bacteria growth.
• Open kettle canning—This is filling jars and closing them without further heat processing. This also includes inverting jars or setting the jars in the sun. Without water bath canning or pressure canning, spoilage will likely occur and food will be lost or people may become sick.
• Electric multi-cookers — While some electric multi-cookers have a “canning” button, no research is available to back up this function. Use these appliances for cooking only!
• The jar sealed, it has to be safe! – What happened prior to putting a lid on the jar is critical to canned food safety. Just because a jar seals does not guarantee safety.

Learn more about safely canning foods at https://www.rrc.k-state.edu/preservation/index.html

Oops! The lids didn’t seal! I used the wrong pressure! Can these jars be saved?

Home canned foods can be reprocessed within 24 hours of initial processing. Remove the lid and replace with a new lid. Change jars if the necessary because of nicks in the jar rim.  Reprocess the food using the proper procedures for that food.

Another option is to store the jars in the refrigerator and use within a few days or freeze for later use. If freezing, be sure to have at least 1 1/2 inches headspace for expansion.

Do not use jars of food that become unsealed during storage for an unknown reason.

http://nchfp.uga.edu/how/store/store_home_canned.html

Natural compounds in some foods, particularly acids, corrode metal and make a dark deposit on the underside of jar lids. This deposit on lids of sealed, properly processed canned foods is harmless. This is commonly referred to as pinholes.

Sometimes they are caused by how the lids are handled. Lifting lids out of water with a metal tool may scratch the enamel on the lid providing a pathway for acids to work their way through the lid. More often, it is simply a chemical reaction with the metal and the food in the jars. As a reminder, today’s canning lids do not require pre-heating prior to applying them to the jar. Simply wash and dry them and they are ready to use.

Pinholes are harmless unless holes go all the way through the lid. Salt can also cause corrosion on lids. Using proper headspace can reduce contact of the food with the lid. If food is stored too long, acids may create pinholes. Discard the contents of any jar if the pitting has gone completely through the lid — the jar would be unsealed and the contents could be unsafe.

Sources: https://nchfp.uga.edu/questions/FAQ_canning.html#13 and https://extension.psu.edu/frequently-asked-preservation-question-pinholes-in-lids