Siphoning (what you call burping) has 3 primary causes: too thick food contents, overly packed jars, and inconsistent pressure during processing in the PC. Well, 4 if you count improperly applied rings. ;-)

The most common cause is the fluctuating pressure issue usually caused by making far too many adjustments in the heat once the processing has begun. Second most common cause is trying to can foods that are too thick and need to be thinned down first.

Per the guidelines, foods such as applesauce, salsas, pie fillings, and similar are supposed to be "soupy" or as I often say "sloshy" (freely moving and suspended in liquid) in the jars. That is the only way to insure proper heat penetration. And excess fluids can be poured from the jars AFTER opening.

Roasted tomatoes canned whole or in halves or are you talking about them roasted to a thick sauce? If you are talking about canning them whole or in halves then the same guidelines apply as for un-roasted ones - you must add add boiling water or tomato juice. You cannot can them without adding some form of liquid and of course they still need to be acidified. Sometimes that added 2 T of bottled lemon or lime juice or 4 T of vinegar per quart is also enough added liquid IF they aren't overly thick to begin with.

If you are cooking them down into a thick lumpy sauce like state and then canning it you would use the processing time for sauce and add tomato juice to thin it down to the proper consistency and then acidify it.

Some other liquid alternatives that have been suggested for thinning are wine or even apple juice. But you will get a flavor change with them.

Hope this helps.

Dave

Hey Dave, Thank you so much! This is really helpful. It's nice to have my theory validated and have the proper word, siphoning.

What I do: halve tomatoes and remove stem, put them into 450 oven until pleasantly toasted. Cool. Slip tomatoes out of skins and puree the skins. Heat guts and puree to boiling. Put into hot jars with acid in the bottom. Process 20 min at 10#.

Normally I roast the halves face up. Today I roasted them face down. This led to lots of juice captured rather than evaporated. (Note: don't use cookie sheets - though tomato juice burning in the bottom of an oven has a pleasant toasted marshmallow smell.) I'm still separating guts from skins but will make sure I have soupy to sloshy consistency in the jars. I'm psyched. Thanks so much for the info & taking the time to type it all up. It's really great to have.

Fingers tightly crossed.

Success! 41 pints of yumminess from 50# of early girls and 6c of chiles and onions. NO siphoning!

One change this year was to cook 10# of halves in a slow cooker for a few hours. This released enough water to share with the roasted tomatoes. Also roasting them face down helped keep a lot of the moisture.

Thanks so much for the advice. I'm so pleased with the results!

So, can you roast tomatoes before making just plain sauce and then BWB them as you would normally do? Is there a specific recipe for canning of roasted tomato sauce? (I searched and this is the most relevant thread I found - but it's really about siphoning, not about canning roasted tomatoes.)

Thanks Dave. But, I see on the Ball website and some other places, that if you add onion and garlic, you can still BWB.

https://www.freshpreserving.com/basil-garlic-tomato-sauce-%7C-recipes-for-tomato-sauce-%7C-ball-preserving-br1045.html

The only difference is roasting the tomatoes first, I guess?

While most Ball recipes are tested and approved we have never been able to document the testing of all their recipes, especially those new ones published in the past couple of years.

That particular recipe (see past discussions here) crosses a line in that it does not meet the USDA guidelines. Personally I am not comfortable with it given all the added low acid ingredients with no increase in the amount of acid over what one would add to just plain tomatoes. To me it flies in the face of one of the cardinal rules of safe canning - low acid vegetables must be pickled OR they must be pressure canned.

The closest USDA approved recipe to it is Spaghetti Sauce with no meat and it requires pressure canning, calls for 10 lbs more of tomatoes, and warns against adjusting the amounts. It is also very similar to several of the USDA approved tomato sauces but all of them require much more added acid

But you are free to use it if you are comfortable with the low margin of safety and yes the only difference is the roasting and insuring a safe level of density.

Dave

I've been wanting to try canning roasted tomatoes, as opposed to the non-roasted ones I do every year. I have always wondered though ... about oil ... typically, when I roast tomatoes for soup or something else, I drizzle them with a bit of oil before roasting in the oven so they don't stick etc. But I did not think you could BWB can oil ... so when you talk about roasting the tomatoes first, do you mean with or without oil? If they are roasted in a small amount of oil and then BWB canned with the usual liquid and acid levels, is that ok? Or would you add more acid? Or would you try to roast them plain and without oil?

I have been wondering about this ...

The easiest solution is just to pressure can them. That is what most do as some like to include other low acid vegetables like onions or peppers in with them while roasting.

But if you can't do that then cooking spray rather than oil is an option. If any oil is used it has to be minimal at best - like wipe the baking sheet with it - then drain them, blot them dry and/or peel it off with the peels. Either way you still have to acidify them.

I prefer to do mine in a roasting basket on the grill. Much faster and you get the flavor but no oil needed.

Dave

That would be lovely, on a grill, but unfortunately not an option for me right now. I do not pressure can, don't even have one, but I do follow the guidelines for canning crushed tomatoes with the lemon juice that are the official guidelines. I do not add any other vegetables as I use them for a variety of things once I open the cans later in the winter. So basically, I can use a bit of cooking spray or wipe the baking sheet with oil (instead of pouring it) and I should be good to go? I am glad to know that ... I have always wanted to try roasting the tomatoes before canning them, just to see how it comes out!! And a wipe-down of oil should be enough to keep them from sticking until the tomato juices start to run themselves... Thank you!! I always know I can count on getting good answers here :)

I roast my tomatoes on parchment paper. I've never had problems with sticking and I've never used oil. Let us know how your tomatoes turn out - yummmm roasted tomatoes.