Sterile jars, and the trade you make either way
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The trade, stated plainly
There are two defensible approaches here and the published guidance supports both, under different conditions. The trade is between work before filling and time in the canner, and picking the wrong one is not dangerous so much as wasteful.
| Jars | Process | What it costs |
|---|---|---|
| Sterile | The shorter time for your altitude | The work of sterilizing, before the batch |
| Unsterile | 10 minutes | Extra heat, which can weaken the set in low-pectin fruit |
Which way to go, and when
The deciding factor is the processing time rather than preference, and it is a single threshold rather than a judgment call. Knowing it removes the decision.
Sterilize when the fruit is low in pectin, because that is the case where the extra ten minutes does the most damage. The guidance says sterile jars are preferred and gives that as the reason, which makes it a recipe decision rather than a hygiene preference.
What sterilizing is not
Sterilizing jars is sometimes treated as a substitute for processing, which it is not and cannot be. The two steps address different things and neither replaces the other. Sterilizing deals with the jar before it is filled; processing deals with the sealed product. Skipping the second because you did the first thoroughly is the one version of this that is genuinely unsafe rather than merely wasteful. The two steps are sequential rather than alternative.
It is not a substitute for processing. The jars are sterilized and the filled jars are still processed; the sterile jar buys a shorter time, not no time.
At volume
Sterilizing every jar stops being practical somewhere above a few dozen, which is one of the points where a batch day starts needing different equipment. That is on making more of it.