Containers

Hot fill and the closure

Updated October 2026

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What happens on cooling The liner has to survive the heat Lug closures go with them Glass and thermal shock Headspace is specified in the regulation And fill temperature is a critical factor None of which makes a hot fill a process References

A hot fill asks something specific of the liner, and only 11 closures here are built for it.

What happens on cooling

A hot-filled jar sealed and cooled develops a vacuum as the headspace contracts, which pulls the lid down. That vacuum is what holds a twist-off lid and it is why the pop is audible on opening.

The liner has to survive the heat

An ordinary plastisol can soften or flow at a hot fill temperature and then not seal properly on cooling. A pasteurization plastisol is formulated for it, and there are 11 of those on this shelf.

Lug closures go with them

Eleven lug and twist closures, which is the format a commercially pasteurized or hot-filled product uses. The combination of a lug closure and a pasteurization liner is the set to ask about, not the continuous thread caps.

Glass and thermal shock

Glass rated to a 300 F fill will take the fill and will still crack from a rapid temperature change. Warming jars before filling and cooling them in stages is the practice, and it is a process control rather than a container property.

Headspace is specified in the regulation

Part 113 defines gross and net headspace separately, measured to the top edge of the container and to the inside surface of the lid. If you are under a scheduled process, headspace is a number you hold rather than a judgment.

And fill temperature is a critical factor

Initial temperature is defined as the average temperature of the coldest container at the start of the cycle. So the fill temperature is part of the process and has to be measured and recorded, not estimated.

None of which makes a hot fill a process

It is worth repeating. These are the right components for a hot-filled product that is also properly processed or properly acidified. They are not a substitute for either.

References

21 CFR 113.3, the definitions for thermally processed low-acid foods packaged in hermetically sealed containers. Paragraph (j) defines a hermetically sealed container as one designed and intended to be secure against the entry of microorganisms so as to maintain commercial sterility; (n) defines low-acid foods as those with a finished equilibrium pH greater than 4.6 and a water activity greater than 0.85, excluding tomatoes and tomato products below pH 4.7; (r) requires a scheduled process at least equivalent to one established by a competent processing authority. law.cornell.edu

21 CFR part 113 generally, which sets the equipment and procedural requirements for thermal processing systems, including instrumentation, venting, temperature and pressure records and operator supervision for each type of retort. law.cornell.edu

Written from federal regulation, not from a production kitchen. Nothing here is a scheduled process, and nothing here is a substitute for a competent processing authority. If you are considering a shelf-stable low-acid product, the first call is to a process authority rather than to a packaging supplier.