Tested and prohibited, never tested at all, and tested then withdrawn

Three claims wearing one phrase

Open almost any list of foods you cannot can at home and you will find the same two words attached to every item on it. Butter: not recommended. Pumpkin butter: not recommended. Pesto: not recommended. Nutmeats: not recommended.

Behind those four identical labels sit four quite different situations. One food has a measured pH and a characterised mechanism behind the refusal [F-9.3]. Two have no research at all, and the people who would have done the research say so [F-9.2, F-9.6]. One had a published process from a university and lost it [F-9.8].

Flattening those into one phrase is not a small editorial sin. It is the reason the whole subject feels arbitrary to newcomers, and it is why a reader who catches one over-stated "no" starts discounting the rest. If every refusal is delivered in the same tone with the same words, the only information you can extract is the tone.

The three categories, stated once

Tested, and the answer was no. Somebody looked, characterised a hazard, and published a refusal. There is a mechanism you can name and often a measurement you can point at. This is the strongest kind of "no" and the least likely to change.

Never tested at all. No laboratory ran the thermal process work. There is no time and no pressure to give you because none was ever generated. This is an absence of research, not a finding of danger, and saying otherwise is lying to you in the cautious direction — which is still lying.

Tested once, then withdrawn. A process existed and was pulled. Stronger than never having been tested, weaker than a food that failed outright, and the rarest of the three.

Every no-process notice on this site declares which of the three it is. That is not decoration. It is the site's method, printed where you can check it, and it exists because almost nothing else in the niche does it.

Why it changes what you actually do

The categories are not a taxonomy for its own sake. Each one implies something different.

If it is a finding, the mechanism usually tells you what the safe version looks like. Density blocks heat, so the tested form is the one that does not block heat — cubes rather than purée. The refusal comes with a route out of it, and you can usually see the route in the reason.

If it is a gap, the question is whether the gap is ever likely to be filled, and whether you can get what you want by another preservation method that does not need a thermal process at all. Freezing needs no schedule, which is precisely why it is available wherever canning is not.

If it is a withdrawal, be careful with old sources. Books, printouts and forum posts predating the change still carry the old process, and they are not obviously wrong on their face — they were correct when written and they cite a real institution. This is the one category where the age of the page you are reading is the whole story.

The withdrawal, in detail, because it is the one nobody covers

The nutmeats case deserves more than a line, and the notice above gives it the space.

What makes it valuable is not the food. Almost nobody is desperate to can walnuts. What makes it valuable is that it is a fully documented example of tested guidance revising itself in public, with the reasoning attached: a process that produced a vacuum, an absence of documentation that it sterilised anything, newer science about an organism nobody was thinking about at the time, and a withdrawal with no replacement offered [F-9.8, F-14.10].

Sit with the middle part of that for a moment. The old process worked, in the sense that jars sealed and stayed sealed. What it never had was evidence about the thing that matters. A sealed jar and a safe jar are different claims, and the gap between them is where every folk canning method lives [F-1.9]. Here is a research centre applying that distinction to its own back catalogue and losing.

That is what a maintained body of evidence looks like from outside, and it is not comfortable. It is still enormously more trustworthy than a source that has never changed its mind about anything.

Reading the category off a source yourself

You can do this without any expertise. The sources usually say which one it is, in ordinary language, and the tell is in the verb.

Look for a mechanism. "Starch interferes with heat transfer during processing" is a finding [F-9.4]. "Oil coats any herb or food placed in it, creating an ideal environment for Clostridium botulinum to grow" is a finding about the environment [F-9.6]. If you can restate the reason in physical terms, you are in category one.

Look for an admission. "We have no safe tested processes to do this" [F-9.7]. "It is not clear what the botulism risk is from such a high-fat product" [F-9.2]. When a source tells you what it does not know, believe it, and file the item as a gap.

Look for a change of tense. "We no longer recommend", "the previous canning process", "there is not a substitute… at this time" [F-9.8]. Past tense about the source's own advice means a withdrawal, and it means any older page you find on that subject is stale.

And check who is speaking. A gap reported by the body that would have run the test carries more information than the same gap reported by anyone else. When NCHFP says nobody knows, that is the people with the equipment saying it [F-14.11].

The full sorted list, every food with its category and its reason, is the short list, and the hub it sits in is what not to can. This page is the method. That page is the application of it.