Pressure canning at odd pressures

Question

I recently acquired a Presto pressure canner model 01781 (23-Quart) which comes with a weight designed to regulate it to 15 lbs of pressure. I also purchased a variable weight regulator (part 50332) which allows pressure to be 5, 10 or 15 lbs. After leafing through the recipes in the instructions I found that they are almost all invariably written with some odd pressure like 6 lbs or 11 lbs.

Can anyone explain how to achieve a stable pressure at one of these odd pressures? Why would the recipes provided all be written for pressures other than what this cooker is designed to produce? Should I simply can at the next highest pressure, e.g. 10 lbs if the recipe calls for 6?

I considered possibly adding a washer to the weight regulating at some in-between pressure but I'm just a bit confused about why I would even need to do that.

Answer 1

I just spoke with someone from Presto - apparently, the pressure is meant to be maintained by adjusting the heat source, and the weight provided with the canner is meant only to build pressure and not as a regulator. They also recommend against adjusting the weight in order to achieve in-between pressures. Not sure why on that last point - I'll follow up here with more info when I hear back from them.

They also sent me a separate recipe book meant to be used with the variable weight and I found that all of the 6 lb recipes are the same when used with the 5 lb weight. And likewise, the 11 lb recipes are the same when used with the 10 lb weight. My best guess is that they are adding 1 lb to the recipes for use with the dial gauge to err on the side of safety, whereas the weight holds a more consistent and predictable amount of pressure.

UPDATE: Spoke with another rep at Presto who indicated that because there is a certain margin of error with the gauge that it would be unsafe to calibrate a weight by reading the gauge. I personally feel that you should be able to logically deduce the achieved pressure with a bit of trial and error using known weights, but I can understand the importance of safety and accuracy when it comes to knowing what pressure you are dealing with.

Answer 2

I agree that those pressures are odd. I haven't personally seen recipes with such non-standard pressures.

I've found that nearly all recipes I use call for either 10 or 15 lbs of pressure. Obviously the higher the pressure the higher the cooking temp and the more the food will be damaged. Ideally you would want the lowest temperature that will render the food shelf stable. In practice, I've found that pressure canning so thoroughly cooks the food that there isn't that noticeable of a difference between pressures. There is a bigger difference in food quality with cooking time. You need to meet the recipe's minimum temperature and time to have confidence that the food is safe.

Therefore, in my experience, you should be fine rounding up to the next pressure you have.

I would guess that you are seeing odd pressures for old recipes or recipes adapted from other countries. Pressure canning and cooking has been around for a long time and is used in many cultures. Old Indian pressure cookers that I've used had pressure weights that translated to very odd values in lbs.