The lid contradiction: preheat, or do not

Two documents that have never been introduced

Here is the shape of it. A federal publication, revised in 2015, hands lid preparation to the manufacturer and then assumes a preheated lid one page later [F-8.1]. An Extension service, publishing in 2023, reports that the manufacturer has stopped recommending preheating and adds that it may be harmful [F-8.1, F-14.2]. Neither document mentions the other.

A third source sits between them. NDSU Extension, in a publication revised in 2022, takes the middle position and describes the change as historical fact rather than as a dispute: lids were traditionally simmered or boiled before use, but "this generally is not the case now", so check the directions on the lid package or the manufacturer's website [F-8.1, F-14.2].

That is three land-grant and federal sources, all current, giving a reader three different impressions of what the correct step is. And a fourth data point makes it worse rather than better: the "place the preheated lid" wording is live on NCHFP's own website today, not just in the 2015 PDF [F-8.1, F-14.2]. The maintainer's site carries it, so a careful reader who goes to check gets the old assumption confirmed.

Why this is drift, not incompetence

It is tempting to write this up as an error. It is more accurate, and more useful, to describe it as what happens when a fixed document depends on a live commercial practice.

The guide made a reasonable decision: the sealing compound is the manufacturer's product, the manufacturer knows how it behaves, so the guide defers. That deferral is the correct engineering call and it is still correct today. What it also does is make one part of the guide's advice dependent on a document the guide's authors do not write and cannot revise.

Then the manufacturer changed its instruction. The guide's deferral sentence stayed right. The guide's incidental phrase — "the preheated lid" — stayed put and quietly stopped matching reality. Nobody did anything wrong at any point, and the outcome is still a document that reads as though it is telling you to do something it never told you to do.

This is the most common shape of contradiction in tested guidance, and it is worth recognising because you will meet it again: not a wrong claim, but a stale assumption embedded in an aside. The same drift at document scale — which text is newer, and how you tell — is on which document is current.

What is actually in dispute, and what is not

Almost nothing is in dispute. Laid out plainly:

Everyone agrees that lids and bands are washed in warm soapy water before use [F-8.1]. Everyone agrees that the manufacturer's current directions govern [F-8.1]. Nobody has published research showing that a preheated lid fails to seal. One source claims, hedged, that preheating may cause lids to buckle, without naming the study [F-8.1]. The guide assumes a preheated lid in a single incidental phrase, without ever instructing it [F-8.1].

Written out like that, the "contradiction" is one aside in a federal document against one hedged sentence in an Extension post, with the actual instruction — follow the manufacturer — agreed by both. The heat in the online argument comes almost entirely from people quoting one of those two sentences without knowing the other exists.

The other contradiction, on the same page of the same guide

While you are on printed page 1-15, there is a second one, and it is tighter: five years and one year, with one sentence between them, in a single paragraph [F-8.2, F-14.3].

It is not a mistake either. It is a product fact and a purchasing recommendation sitting next to each other without a connecting sentence, and a reader who takes either one as the whole answer walks away with a different policy. The full quote is in the slab above, because with a passage like this the only fair way to report it is to print all of it and let you see the sentences in order.

That is a habit worth borrowing when you read anything on this subject. A quoted fragment can be verbatim and still misrepresent the source, and the way you catch it is to open the source and read the sentence on either side.

What to do tonight

Wash the lids and bands in warm soapy water, not in the dishwasher [F-8.1]. Read the packet the lids came in and do what it currently says. If it says nothing about heating, do not heat them.

If your lids are old enough that you cannot remember buying them, that is a stock question rather than a safety question, and the honest state of the evidence is on this page: the guide's five-year figure runs from a manufacture date you do not have [F-8.2].

And when you next see a page confidently telling you to simmer your lids, or confidently telling you that anyone who does is out of date — now you know that both of them are quoting something real, and that neither of them has read the other one.