Thus follows a few questions. My apologies for the length of the post.

I will appreciate all replies in advance. Thank you for your time and for sharing your experience.

I have discovered a love for fruity salsas.

I have a salsa verde (tomatillo) recipe from the NCHFP that I enjoy. Here it is http://nchfp.uga.edu/how/can_salsa/tomatillo_green_salsa.html.

I would like to add some peach to that recipe and wondered what you thought about the safety of that.

The NCHFP recipe calls for 15 minutes in a BWB (pints). Peaches have a similar processing time (20 minutes).

So, if I make a batch that is 3/4 NCHFP recipe and 1/4 peach (cooked), and do BWB for 20 minutes, does that seem likely to be a safe recipe? I recognize that there is no such thing as absolute safety.

Another question along the same lines:

I know from reading that two major variables in determining safe canning are pH and density.

pH determines if pressure canning or BWB canning are appropriate.

Does density account for different lengths of canning in similar products? For example, I see that canning times on acidic fruit vary from 10 (grape juice) to 25 minutes (peaches, pears and plums) for pints. Does that reflect the fibrous nature of the fruit purees? Seems like the fibers would affect how convection carries the heat from the outside of the jar, in contact with the boiling water, to the inside of the jar. Grape juice in contrast would conduct or circulate (by convection) the heat more easily.
And lastly,

I find myself trying to understand the principles so that I can understand why the safe recipes are the way they are and what substitutions I can safely make.

Is there a good resource on line of in a book about the science of canning that I could read in order to understand the underlying principles?

Since you're interested, there's a copy of the abstract linked at the bottom of the page.

I know of no single text for home food preservation per se. I used to have one link for a Canadian food study manual, but it's dead.

The issues cross disciplines including bacteriology and thermodynamics, among others. But the NCHFP does provide copies of some research on their site (including one on acidification of salsas) and that can be a good beginning. Also you might want to contact a regional land grand university with a strong food sciences program and check out their reading lists and recommendations.

Be sure you don't get to the point where you know just enough to be dangerous! There's a reason why a degree in the field takes years.

I think for most experienced canners it's a cumulative process of reading and study and asking questions. Even then we don't have access to the sophisticated testing facilities or resources of private corporations or universities and that limits what we can reasonably (and safely) do.

Carol

Myself, I would not change things.

I'm thinking that pH would be the most important, density being second important. pH is tricky, whether in canning or planting.

I'm sure there is someone on here that will answer you in more detail.

Myself, I would not change things.

I'm thinking that pH would be the most important, density being second important. pH is tricky, whether in canning or planting.

I'm sure there is someone on here that will answer you in more detail.

But as a general principle, when canning foods, because of the storage environment that is created, one has to very carefully limit their spirit of adventure. :-)

And when experimenting you can't make the mistake of generalizing from one recipe to another. Each recipe and ingredient has to be evaluated on its own merits. So neither processing times nor % of a recipe are valid comparisons. As Carol said in this case it is the relative pH of the peaches compared to the other ingredients in the recipe that counts.

pH and density are of equal import in determining both the type of processing and the time of processing.

NCHFP does offer an online basic course you can sign up for. It doesn't teach all the theory details but there are certified classes available for more education in home food preservation.

Dave

And Dave, thanks for the reference to the NCHFP online training. I have requested the course and will give it a try.

I also noticed that they offer webinars. I will check those out as well.

Nancy