Expert: Carol Schlitt - 9/5/2007

Question
Hi- I am new to home canning- I canned tomatoes this weekend according to a home preservation book....on one batch, though, we decided to get creative- and slow roasted a bunch of tomatoes with a little garlic balsamic and olive oil and then canned them- we did put in the same amount of citric acid as the whole raw pack tomatoes recipe called for....I am just concerned the oil in the recipe may alter the pH balance...can you tell me whether or not that is so...we added 1/2 teaspoon of citric acid per quart of tomatoes.

2nd question- when a recipe calls for "head space"- say 1/2 " head space- is the a 1/2" from the very top of the jar? or 1/2" from the threading of jar?  Does too much head space make a safety concern?

Thanks for your help!

Maria

Answer
Hi Maria,

Yes, when you change a recipe adding ingredients such as oil you change the pH and viscosity of the product. Without a tested recipe for a roasted garlic, balsamic and olive oil tomato product, I could not recommend canning this product. Even with the 1/2 teaspoon of citric acid, the pH could be compromised to a point that it could support the growth of harmful bacteria.

Head space refers to the space between the top of the jar and the food.  Usually, 1/2" headspace is from where the threads start to the top of the jar.  And yes, too much head space is a safety concern.  Too much means that a lot of air has to be expelled from the jar to get a correct vacuum. The amount of headspace needed depends on the type of food being processed. If the jars are filled too full (leaving too little headspace) the contents may boil out during processing. If too much headspace, the processing time may not be long enough to drive out all the extra air at the top of the jar.

A great website you should check out is the National Center for Home Food Preservation.  Here you'll find research-based, non-commercial answers to your questions:

http://www.uga.edu/nchfp/index.html

Good luck canning!

Carol