Time and Pressure Adjustments When Canning At Different Altitudes
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The first thing you should do when you begin learning about home canning is to find out what elevation (or altitude) you live at. I know elevation and altitude mean different things, but for the sake of canning, we’re going to use them interchangeably. This is also known as the feet above sea level you are at. Chances are if you live at a higher altitudes, you’ve already learned the basic concepts on how to adjust baking and cooking due to the lower air pressure and lower temperatures that water boils. High-altitude canning is no different.
The higher the elevation you go, the atmospheric pressure decreases and the boiling point of water decreases. I’ve read it decreases about 1 degrees F every 500 feet higher you go. To adjust for this temperature difference, you will either adjust your processing length of time or weight of pressure, depending on what you are canning. All the processing weights and times given in canning books, and by me, are for processing food at or below 1000 feet. My water is boiling hotter down here in the valley as compared to you mountain folk! I always mention in my recipes to adjust your time or weight for altitude.
If you’re going to be difficult and act like you don’t have internet or a way to find your altitude, take a pot of water with a candy thermometer and measure the temperature your water boils at. 212 degrees F is the baseline. For every degree you are under, add 500 feet to 1000 and you can safely assume that is your elevation. Adjust your times accordingly.
Otherwise, simply type into your search engine “altitude + zip code” and hit enter. There are also maps you can find of major cities in your state and their altitudes. I bet an ole rand mcnally has one. The downside is that some major cities are not the elevation that you actually are. I know for Ohio the only elevation given is Akron… which is about 200 feet higher than where I am. It says 1004 feet, so I’d be pressure canning at 15 pounds when I only needed 10. Overprocessing much?
Low Acid Canning
For low-acid foods, you will be utilizing a pressure canner.. usually. Unless you’re a rebel, then carry on. But, I choose to pressure can my low acid foods. Low acid foods are your vegetables, like green beans, potatoes, and meat and broths. Things that have a pH above 4.6. When canning at higher elevations, pressure requirements change to be able to bring the canner to 240 degrees F, so you have to use a higher weight or pound of pressure to get that, while using the same amount of time for the canning process. To elaborate, canning quarts of beef at 1000 feet would be 90 minutes at 10 pounds of pressure while canning quarts of beef at 8000 feet would be 90 minutes at 15 pounds of pressure. Same times, different weight.
There are two types of pressure canners and which type you have affects the amount of pressure you use at high altitudes:
Weighted-gauge pressure canner
A weighted-gauge canner has a weight you place on a valve stem to bring the canner to proper pressure. Some have a gauge, some do not. We don’t really care about what the gauge reads anyway and want to go off of the jiggling and hissing of the weight to ensure adequate pressure. This is the type of pressure canner I have. These canners have 3 weights to choose from: 5, 10, and 15 pounds. 5 pounds will not be used for low acid foods, ever. You will need to know your altitude so you can properly choose which weight you need. This one’s an easy choose. 1000 feet and under will use 10 pounds and anything over will be 15 pounds. The downside is, if you’re at 1100 feet, you’re canning at a weight that is for someone at 10,000 feet as well, which can result in softer food that feels a touch overprocessed. This is where the next kind of pressure canner may be nice for you.
Dial-gauge pressure canner
This type of pressure canner goes entirely off of a gauge with no weight. It allows you to more fine tune your weight, especially for those living at elevations above 1000 feet. So for the person living at 1100 feet, they can use their dial-gauge canner and can at 11 pounds of pressure instead of 15 pounds. The downside of this canner is that you have to watch the gauge constantly to be sure it stays at the proper weight… which is boring. They can also be touchy and hard to regulate until you get the hang of it. If at anytime the pressure dips below what you are supposed to be at, you have to restart the processing time. This is massively inconvenient. You also are reliant on the gauge and if the gauge chooses to fail, you’re up a creek with no paddle for a canner until you can get the gauge replaced. The dial gauge must be tested for accuracy every year, too, which makes this design very unpopular.
High Acid Canning
Any recipe or food with a pH of 4.6 or lower is preserved using two types of canning: water-bath canning or steam canning. Since at higher altitudes water has a lower boiling point, the processing length of time is adjusted. There are charts in most canning books, like the Ball Blue Book, and also on the National Center for Home Food Preservation (NCHFP) website on how to adjust your canning times according to your altitude in increment of 5 minutes up to 20 extra minutes. This time addition will be the same for every single water bath processing recipe. When using a steam canner, be sure and read the manual that comes with it to verify you have it up to temperature and enough steam trapped to start your processing time.
Since we are high acid canning, there is no concern for clostridium botulinum because it can’t survive in acidic environments. The heat of the boiling water or steam with low acid canning is used to heat the jar contents up enough to destroy enzymes, bacteria, and more that can cause spoilage. When heating at lower temperatures due to altitude, we then rely on the increase of processing time to hold the food at that temperature for longer to prevent these enzymes and pathogens from spoiling the food. Heat and time are huge factors and someone super smart once researched and adjusted times based on time and temperature for food to keep and I think that’s super cool!
I hope this sheds some light on understanding pressure and time adjustments that are necessary for preserving home-canned foods safely at home.
