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Jam and preserves
All Containers›Shop by use case›Jam and preserves›Making a batch›Wiping the rim and adjusting the lidsShop all jams and preserves →
Making a batch

Wiping the rim and adjusting the lids

By Dwight Davis, Founder

Updated

On this page4
The guide puts three things in one sentence: wipe the rims with a dampened clean paper towel, adjust the lids and process. Each of the three is load-bearing and the first is the one that gets skipped.

Wiping

This is thirty seconds of work that decides whether a batch seals, and it is the step most often done quickly at the end of a long day. Jam is sticky and a filled jar almost always has something on the rim whether or not it is visible.

Dampened, and clean. A dry cloth moves syrup around rather than lifting it, and a cloth that has done five jars is carrying sugar to the sixth. Imperfect sealing is a published cause of spoilage, and a trace of product on the sealing surface is how imperfect sealing happens on a bench where everything else was right.

Adjusting, not tightening

The wording in the published guidance is deliberate. A band that is too tight prevents air escaping during processing, which is the opposite of what you want, and the instinct to make it secure is exactly the instinct to resist.

  1. Place the flat lid on the clean rim, sealing compound against the glass.
  2. Screw the band down fingertip tight. It is holding the lid in place, not making the seal.
  3. Do not force it. Air has to leave the jar during processing, and a band tightened down hard can stop it.
The seal is made by the vacuum as the jar cools, not by the band. That is why bands come off after cooling and why a jar is stored without one.

Then process

The gap between filling and processing is short for a reason, and treating it as a convenient pause is how a correctly made batch fails at the last step. Fill, wipe, lid and load as one continuous action rather than filling a tray and coming back to it. A tray of filled jars waiting for attention is a tray of jars cooling towards the temperature at which the seal stops forming.

Straight away. A filled jar standing on the bench while you fill the rest of the batch is cooling, and the process time assumes it went in hot. Time in the canner is on time in the canner, by altitude.

References

United States Department of Agriculture. Complete Guide to Home Canning, Guide 7: Preparing and Canning Jams and Jellies (rev. 07/2015). National Center for Home Food Preservation. nchfp.uga.edu
National Center for Home Food Preservation, University of Georgia. Causes and possible solutions for problems with jellied fruit products. nchfp.uga.edu
Written from federal regulation and published extension guidance, not from a laboratory. A standard of identity is a federal floor and your state adds to it. Anything here is a starting point for a conversation with your state department of agriculture, not a determination that you comply.