I live one mile from the beach in Southern California. When I water bath can at home, I’m at sea level. So, I just follow the recipe and I’m good to go.
But when I can at my family’s 1892 Farmstead (which is at 2,400 ft), I have to make adjustments to my processing times because I am canning at a higher altitude.
The idea of making adjustments can confuse newbie canners, especially since many recipes assume the canner just knows how to do this. Unfortunately, it is not always spelled out.
Even if you are an experienced canner, it helps to understand the “why” when it comes to altitude adjustments.
So in today’s post, I explain why altitude makes a difference in your water bath processing time and how to adjust for it.
The Process Time of a Recipe:
In water bath canning, the food is held at the boiling point for a certain amount of time and that kills the bacteria that cause spoilage.
At the end of every recipe, it will state the amount of time you are to boil the jars in the water bath. You are also supposed to adjust that time based on your altitude.
How Altitude Affects The Boil:
At sea level, water boils at 212 degrees F. But as you go higher in elevation, water boils at a lower temperature.
For example, water boils at just 204 degrees F at 4,000 feet and at 203 degrees F at 5,000 feet.
The Scientific Reason For This:
This reduction in the boiling point happens because of the decrease in air pressure.
In other words, there is less pressure pushing against the water molecules and preventing them from vaporizing into steam when they are heated.
So at higher altitudes (with less pressure), water molecules get agitated and break apart (turning to steam) more easily than at a lower altitude with more pressure holding them together.
The Bottom Line:
What is most important to understand is that when you boil water to make a cup of tea in the mountains, that water is really not as hot as it is when you boil water at the beach.
Why Does This Matter in Canning?
This natural phenomenon is important in canning because we are relying on temperature to kill the bacteria that causes spoilage.
If the water is not as hot as required, it will take longer to kill the bacteria at that lower temperature.
So, all you have to do to be safe, is process your jars a few minutes longer so that the temperature has enough time to kill the bacteria in question.
How to Adjust for Altitude:
There are numerous online charts for altitude and many recipes will list the adjustments within the recipe. I have listed them here for you as well:
0-1000 ft. - Follow the time in the recipe
1,001 – 3,000 ft - Add 5 minutes to your processing time
3,001 – 6,000 ft - Add 10 minutes to your processing time
6,001 – 8,000 ft - Add 15 minutes to your processing time
8,001 – 10,000 ft - Add 20 minutes to your processing time
Over 10,000 ft – Why are you canning? Come down off that mountain before you hurt yourself.
How to Find Your Own Altitude:
What if you are canning somewhere and you don’t know your altitude?
The answer is simple. Google it.
Do a search on “your city location and altitude” and Google will tell you what the altitude is. Then check the chart and add the appropriate extra minutes to your processing time. You can also check with the your local county extension office, but Google is faster…naturally.
So, don’t be worried about the altitude adjustments. As long as you understand the reasoning behind it, it is easy to do!
What is the highest altitude you’ve canned or cooked at?
For me, it was 6,000 feet. Baking a pie was…a little challenging.