Filling hot, and why a funnel
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You need
- A wide-mouthed canning funnel
- A ladle or a heatproof measuring cup
- Jars at temperature, not cold from a cupboard
- A damp clean paper towel
The steps
The sequence matters more than any single step in it. Hot product into a hot jar, promptly, with a clean rim, is the whole of it, and each of those three is doing a specific job that the next one depends on.
- Work straight from the pan, with the product still hot.
- Set the funnel in the jar and ladle to the headspace the recipe gives.
- Lift the funnel without dragging it across the rim.
- Wipe the rim with a dampened clean paper towel.
- Adjust the lids and process.
Why hot, and why promptly
This is the part that explains the rest. A hot fill is not about the product being pleasant to pour; it is what makes the seal form as the jar cools, and the window in which it works is shorter than it feels at the stove.
A jelly allowed to stand before it is poured sets partly in the pan, and pouring then breaks the gel that has formed. That is a published cause of cloudiness, and the same delay is what puts trapped air into the jar.
The rim
The rim is where a careful batch gets undone in the last ten seconds. Jam is sticky and a filled jar almost always has something on the sealing surface, whether or not you can see it.
Wipe every jar rather than the ones that look like they need it. A smear too thin to notice is enough to hold the lid a fraction off the glass, and a seal that fails for that reason usually fails days later on a shelf rather than visibly in the canner.
Wiping is an instruction in the guide, not a courtesy. A trace of sugar syrup under the lid is a path for air, and imperfect sealing is a published cause of mold and fermentation.