Pressure canning at odd pressures


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.

Best Answer

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.