Keeping it clean while you go
Updated
The rim
Everything about the seal happens in a quarter inch of glass, and it is the part most likely to have something on it precisely because it is where the product passed on its way in.
Wiping the rim is a published instruction, not housekeeping. A trace of syrup under the sealing compound is a path for air, and imperfect sealing is a named cause of mold and fermentation.
The outside
A sticky jar is a presentation problem and a shelf-life problem at once: it attracts dust, it marks the label, and it tells a buyer something about how the rest was made.
A drip down the side dries to a varnish, and a label applied over it lifts within a month. It also makes a jar that feels wrong in the hand, which a buyer notices before they read anything.
The technique
- A bowl of warm water and a clean cloth beside the funnel, not across the kitchen.
- Wipe the rim of every jar, not just the ones that look messy.
- Change the water and the cloth when they go sticky. A sticky cloth moves sugar from jar to jar.
- Wash and dry the outside of the jars after they have cooled, before labeling.
Why after cooling and not before
The timing is counterintuitive and it matters. Cleaning a jar before it has cooled risks the seal that is still forming, and a jar handled warm can lose a vacuum that had not finished setting. Leave them alone for the full cooling period and clean afterwards; the stickiness will still be there and the seal will not be at risk.
Because a jar fresh out of the canner is wet anyway, and because you should not be handling jars while the gel is setting. Labeling comes after the jars are cool and dry, which is also when the seal check happens: cooling, and not moving it.