Canning season is in high gear and we’ve received a lot of questions about selecting the proper lid for your canning jar. We’ve put together a basic guide that will help you determine the proper CT lid (continuous-thread lid) for your canning needs. Continuous thread (CT) is the Mason-style closure mechanism where the jar and lid are both threaded in one continuous bead around the entire circumference of the opening; also referred to as “screw-on”. Both the 2-piece and the 1-piece canning lids must have a plastisol liner – a rubbery gasket that is attached to the lid and provides the seal on the finish of the glass jar.
Find the recommended and approved preserving process for that type of product or combination of products. If you are selling your product, you will want to get in contact with your local/state processing authority or Ag Extension office to see what additional guidelines or requirements are in place. You’ll also want to check out this resource that addresses topics that surround those wanting to sell their products. These recommendations will help to determine what type of process(es) you will want or need to follow. The National Center for Home Food Preservation is a good resource for general home canning guidelines.
Your process may determine which type of jar and/or lid you use. (See the 3 basic processes below.) If you find that you have a choice of processing options, this may open the door for you to use something other than the traditional 2-piece lid. This may also give you the option to use a jar other than the traditional mason jar.
Once you determine your process, you may then have some other things to consider.
Preheat your jars (either in a large water bath or in the oven), and using a small saucepan, preheat your lids in a simmering water for 5 – 10 minutes. Pour HOT contents into the pre-heated jar, cap immediately with a pre-heated lid. As soon as it is capped, the plastisol (already softened in the simmering bath) begins to form a seal around the rim of the jar. As the contents cool, the vacuum is created, the lid becomes concave. Whether or not you actually hear a “pop” will depend on the type of lid, but you should be able to tell visually if the lid has created enough vacuum and a seal. Some folks still feel the need to water bath these jars…which can affect the vacuum and cause them to NOT seal properly. Our CT jars and Lug jars are compatible with this method so your lid choices will depend on the jar that you choose.
If the product is already hot, the jar should be preheated as well to avoid thermal shock. The standard Plastisol lids are compatible with shorter water bath processing (such as hot-pack jams/jellies). Longer water bath process times usually require the Hi-Heat Plastisol.
It is important to follow the guidelines for your particular food as they can vary greatly.
Whether contents are raw or cooked, the jar should be preheated to avoid thermal shock. The need for preheating of lids is subjective as the heat created in the pressure canner will be sufficient to soften the plastisol and the temperatures in the canner are sufficient for any microorganisms present on the lid. It is important for these jars to vent properly, so be careful to not over-tighten.
Many variables may impact your sealing rate. Whenever a process is performed by hand, there are variations. Here are a few things to consider as you preserve…whether you are starting out, or trying your hand at a new process, new foods or a different style or brand of lid or jar.
Compatibility of jars and closures with product and process is the responsibility of the user. Please consult your process authority and test packaging components for suitability.