A very common question here with many past discussions about it that the search will pull up if you are interested in reading them. But basically it boils down to, it is so they can be pressure canned for comparatively short periods of time and at such low pressures resulting in better quality. Without the pH adjustment they would require higher pressure and/or longer processing times.

And it isn't just the online instructions. So do all the approved current canning books.

Dave

So how long and under what pressure at 1000 ft elevation can tomatoes be safely canned without added acid?

ALL approved instructions tell to add it at any elevation. Is there a reason for you asking the question?

I would like to can my tomatoes without the addition of acid. So I'm wondering how long to pressure can them so I can do this. You indicated that pressure canning them for a shorter time wAS why acid needed to be added

<So how long and under what pressure at 1000 ft elevation can tomatoes be safely canned without added acid?>

Per the guidelines, all methods for canning tomatoes require the addition of acid in some form because tomatoes are low-acid produce. That has been the policy since the early 1970's research on the issue. And with ongoing research the list of products that require acidifcation is expanding. So there are no calculated and tested methods or times for canning them without added acid.

So it becomes a do-at-your-own-risk issue. You can choose to ignore the guidelines and can them as you wish and estimate your own processing times if that risk and the resulting quality are acceptable to you. All I can tell you for sure is that the processing time required would vary depending on if you were canning them whole, in halves or quarters in water, crushed, with no added liquid, or in halves or quarters in juice. Each method would require different processing times because of the varying density issues.

So in theory you could process them for 35-40 mins at 11 lbs. and probably be safe but there are no guarantees of that. And the shelf storage life of them would be substantially reduced without the added acid since the pH of tomatoes does not remain stable but rises over time on the shelf. The added acid prevents that from happening.

Given the small amount of added acid called for it just isn't an issue for most of us. That is especially true when one uses citric acid rather than the bottled lemon juice. Using vinegar is the least popular by far. Personally I have been canning them for over 50 years, long before the current guidelines were put into place in the 70's and I find the end result with the acid added to be better - less seal failures, better color retention, and fresher taste than we had in the past.

Dave

Sorry our posts over-lapped.

No I I didn't indicate that "pressure canning them for a shorter time wAS why acid needed to be added" was the only reason. What I said was "it is so they can be pressure canned for comparatively short periods of time and at such low pressures resulting in better quality."

Big difference. For example, whole or halves in juice 25 min at 10 lbs of pressure results in a much better quality than does 85 mins in a BWB not to mention it is easier to do. 10 mins at 10 lbs. vs 45 mins in BWB for whole or halves in water results in a much better quality. For crushed it is 20 mins at 6 lbs. vs. 45 mins. in BWB.

If end quality is no issue then BWB. If it is then PC. But either way the added acid is required by the guidelines simply because tomatoes are low-acid or at best borderline low-acid so safe, stable, shelf storage requires adding acid.

As I mentioned above there are many very long past in-depth discussions here about this the search will pull up if you want even more opinions. Have you tried canning them with the acid? You may find, that like most of us, it isn't an issue at all.

Dave

I have always canned with the acid with waterbath. But I was hoping to pressure can so I could save time. And not heat up the house so much. Why don't we have to add acid to things like string beans or chicken stock?

<But I was hoping to pressure can so I could save time. And not heat up the house so much.>

You can still do that with the acid added. It does reduce the house heating IMO but there is some debate as to whether it actually saves time. It does for me because I run 2 separate PCs alternating them so the heat-up and cool down waiting time isn't a problem for me.

<Why don't we have to add acid to things like string beans or chicken stock?>

Because they both have much lower density (faster heat penetration) than tomatoes do and they both have longer PC processing times than tomatoes.

Dave