Thursday, April 21, 2011

Pressure Canning Adventures: Vegetable Stock

A month, or so, ago, I agreed to teach a pressure canning class in the summer; it sounded so easy--just teaching a single-item pressure-canning workshop with tomatoes. We'd just gotten a pressure canner, and it was gracing the kitchen with its shiny presence; I had read the instructions, and everything made perfect sense. I had seen fellow bloggers' posts about pressure canning, and the process seemed very clear. I felt ready. I felt ready, that is, until the pressure canner was actually on the stove, and I had to begin the process; then, at that very moment, some little voice inside of me commanded me to be terrified of pressure canners. Once I put the couple inches of water into the canner, once I filled the jars half-way with water, and began bringing the contents to a simmer, I understood all the fears of pressure canning. "What if it explodes," I said to myself, "what if it doesn't work and never achieves the pressure?" "What if my jars all break once it reaches pressure?" All those people who had come to my canning workshops and told me that they have a pressure canner, but are too intimidated by it, suddenly made sense. I swear, if I hadn't spent 4 hours making vegetable stock, I would have stopped right then and there...
The pressure canner, next to two 7-quart pots of stock.

I also knew that I couldn't back down because I had to learn how to pressure-can before I could teach others how to do the same--and overcoming my irrational fears of pressure canning meant that I could dispel similar fears in others.
(I don't know if the pictures quite portray the stature of this pressure canner. It's not only large, but it's also made of cast aluminum, and thus quite heavy. This model also doesn't have a rubber gasket to create a seal between the canner and lid; the six thumb screws hold the lid in place.)
One jar of stock among others.

The weight is on, and the pressure rising
So I took a deep breath, and started the process.

Just as with water-bath canning, it is important to get the jars hot before filling them. Jars are definitely made to withstand high heat, but don't do well with quick temperature changes and can break because of temperature shock. Jars are half-filled with water, and then placed into the pressure canner (which is filled with 1.5 or 2 inches of water); the whole thing is then brought to a simmer over medium-high heat. It's not necessary to sterilize the jars ahead of time, as they will become hot enough during pressure canning to kill off any and all unwanted bacteria.
Once the contents of the canner were happily simmering (not to self--this takes longer than expected), I took out one jar at a time, emptied the water, and filled it with near-boiling vegetable stock until all the jars were full. Then, I screwed the lid on, turned up the heat, and waited for the steam to vent for 8 minutes before putting the weight on. Once the weight was on, the pressure started rising. I had to regulate the heat a couple times to make sure that the weight wasn't "jiggling" too often--this indicates that the water is evaporating too fast, as the weight "jiggles" to release steam and to keep the canner from overshooting the pressure.
Once the gauge reached the appropriate pressure, I started the timer--35 minutes for vegetable stock; afterwards, I just turned the burner off, and let the canner de-pressurize on its own overnight. All seven quarts of the vegetable stock sealed quite firmly, and I'm looking forward to having those to use throughout the next few months.

A few things of note: because this was my first time handling the pressure canner, Matt helped me throughout the process--he encouraged me, read and re-read instructions, helped me screw on the lid, fill the jars, etc. If you're tackling pressure-canning, I highly recommend doing it with a friend. Secondly, the process took a lot longer than I expected, just because I wasn't quite sure what to expect: the canner took a long time to come to a boil, to come to pressure, and to de-pressurize. When I started out, I thought that I'd be able to just pop off the lid once it was done, and to take out the jars for instant canning gratification. But that's not so. The large warning label on the lid of the canner warns not to take the lid off too early, lest you want to acquire steam burns; thus, I decided to wait to extract the jars until the following morning. This means that if I'm teaching a class on pressure-canning, I will need to build in the time to let the canner come down to normal pressure.
Overall, I'm so glad that I tried pressure canning now, so I can have plenty of practice before I am canning corn and tomatoes. I wasn't thrilled about canning the stock (I make bullion to use in soups, usually), but it was worth it to have the practice.

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