Two Is Better Than One…Especially When It Comes to Canning Lids
The current difficulty in some areas of the U.S. of obtaining needed canning supplies is causing a lot of anxiety. A particular complaint is an inability to find canning lids.
Some, like myself, have plenty of jars because they tend to accumulate over the years if you regularly can. And, when people find out you can, they give you jars. I have a friend who had attended a few of my canning classes and was packing up to move out West. He did not want to take all of the canning jars he inherited from his mother, so he gave them to me; I got the mother lode, no pun intended.
This canning season I have found myself short of half-pint jars, this is the size I give away as gifts, so I rarely have extra. But what I really needed were lids for all of the quart size jars I reuse to preserve food for pantry storage, and I am not alone. I have received emails from all over the country from people saying they can’t find needed canning supplies, particularly lids. They also want to know if I have heard back from Newell Brands because they read my previous article on this topic? No, I have not. Another person asked if they could use the vintage zinc lids they found online because they were never used? I let them know that type of lid was discontinued back in the ’60s and it was not recommended.
With all the difficulty of sourcing canning supplies, you may be wondering why you should add to the frustration by following the USDA lid recommendation for canning – the standard two-piece metal system? You should, because based on past research and experience, it is the best choice.
Standard Two-piece Metal Lid System
A two-piece metal lid is made up of a single-use flat metal lid held in place with a metal band. The bottom of the lid has an enamel coating and a channel filled with a sealing compound. During the canning process, the sealing compound softens allowing air to escape while covering the jar-sealing surface. Upon cooling, the compound hardens forming an airtight seal. Unused lids will work well for at least five years from the date of manufacture. Older lids may fail due to the age of the sealing compound.
Reusing the flat metal lid is not recommended due to a higher risk of seal failure because the sealing compound is often dented after use and does not cover the jar sealing surface properly and/or there is not enough sealing compound left in the well to form a proper seal on the jar.
If you have tried to reuse a lid and have experienced a sealing failure, there are steps you can take to still enjoy your home-preserved food. For safety, jars that were properly processed, but did not seal can either be reprocessed within 24 hours, frozen or refrigerated, and eaten within a week like any other home-cooked food.
With properly followed steps, reprocessed canned foods will be just as safe as properly canned foods with good seals. Reprocessing does reduce the shelf life and quality due to extensive softening of the food.
When used as intended, with recommended headspaces, the standard two-piece metal lid system first; allows for very good exhaustion of air from the headspace during the canning process (this is necessary for the formation of a strong vacuum), second; provides a visual indication that a vacuum has been pulled and maintained, and third; maintains an excellent seal throughout storage of the canned food.
Reusable plastic canning lids with a rubber ring for sealing have been in the marketplace since the mid-1970s; they have been receiving more attention due to the current difficulty in some locales of obtaining two-piece metal lids. A set consists of a flat white plastic lid and a separate rubber ring. The user is told to use the metal bands that come with the standard two-piece metal lid system.
The choice of a reusable lid by itself would not impact the safety of the canning heat process in terms of killing bacteria. If the lid is used on the correct shape and size canning jar, and if the food is prepared as described for the intended canning process, and all other canning steps take place, then the canning process should work as expected for killing bacteria.
The Safe Plates Food Safety Team (NC State University-based and of which I am a member) does not have a basis for telling people not to use reusable lids, but neither do we have enough information about their performance to endorse or recommend them. Individuals choosing to select this type of lid can accept the manufacturer’s guidance and determine if they are satisfied. To our knowledge, there is no publicly available research data on the use of reusable lids.
Information Needed to Recommend Reusable Lids
To determine whether or not reusable lids could be recommended, the following would need to be known. First, the rate of sealing success or failures – do the jars fail to seal at a certain rate, or is the seal pulled after canning as reliable as the standard two-piece metal lid system? And, how well does the seal hold up over time in storage?
The strength of the seal is important because of the potential growth of food spoilage and foodborne illness-causing microbes that can gain access and contaminate food in weakly sealed jars.
At this time, we do not have any documentation that tells us the number of times the lid and rubber ring can be reused successfully or how strong of a seal is pulled using the directions. The “strength” of the seal relates to how much air gets forced out of the jar during the processing time. The better the seal (the more air forced out), the better quality of the food during storage. There are testimonials about the effectiveness of one-piece lids, there is just not enough research data or experience with this type of lid to answer necessary questions about them.
Recently I spent 7 hours canning 19 pounds of meat. The process involved preparing the meat, processing the first canner load, allowing the pressure canner to cool, and then repeating all the steps with the remaining meat. All of my jars had excellent seals.
I am glad that all of the jars sealed, it would have been a disappointment if they had not and I had to choose between reprocessing, freezing, or refrigerating and eating within a few days. But, not as disappointing as canning food and discovering unsealed jars after more than 24 hours have passed since processing. In that case, the contents of all of the jars would have to be discarded because too much time has passed to reprocess, the food is not safe to eat. Has this ever happened to you?
The current lid recommendation provides the assurance that if all of the steps are followed home-canned food will be safe and of good quality. Following the recommendation also reduces the risk of wasted time and/or wasted food in cases where reprocessing is necessary, or cannot be carried out because too much time has passed.
The recommended two-piece lids are not perfect 100% of the time, failures can occur due to manufacturing defects. I personally have not experienced lid failure due to manufacturing defects, my lid sealing failures are due to user error (not measuring headspace and over-filling jars or over-tightening bands) but my technique gets better every time I can.