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Canning 101: Can You Safely Can on a Glass Top Stove?

Andrea's stove

Obviously, this is not a flat top stove. I didn’t have a picture a picture of one, so this is standing in.

In the last two days, I’ve gotten three different questions about canning on glass top stoves. And so, I figured it was high time that I added a blog post to the Canning 101 archive to explain why it’s not recommended and how you can potentially work around those warnings. Read on for more!

If you are the owner or regular user of a glass top stove, you may have heard that you’re not supposed to do any canning on your smooth, easy-to-clean stovetop. For long time canners who find themselves with these stoves, this news can be quite a blow.

There are three primary reasons why manufacturers recommend against canning on a glass top stove. The first is that many older canners have concave bottoms. When you combine a concave bottom with a flat surface, heat, and water, there is a risk that a seal will form between the canner and the stovetop. It’s not a huge deal until you go to move a canner that has suctioned itself to the stove. The seal can be strong enough that attempting to move the canner can result in a cracked or shattered stove top (this can also happen if you put a lid on your flat surface).

The second reason that it’s not recommended is that a full canner load of seven quart jars can be heavier that the stove top can bear. Even if your pot has a flat bottom, if it ends up weighing more that the glass surface can bear, you can still end up with a broken range.

The third reason is that some glass top stoves cycle the heat on and off, and so aren’t able to hold a steady boil. If you can’t hold a canner at a constant boil, you cannot guarantee that you’re getting the full level of heat penetration necessary for your preserves to be sterilized and safely shelf stable.

Happily, not all is lost for potential canners with flat glass top stoves. You can eliminate the risk of breakage through suction by using a pot with a flat bottom. A light-weight stainless steel stock pot (like this one) works well as a canning pot and will never seal itself to your stove. It also has the added benefit of being light enough to prevent the surface from cracking or breaking due to too much weight.

There is the issue of maintaining a rolling boil. Some stoves can do it and others can’t. Test your stove by bringing a pot of water to a boil and tracking the temperature with a candy thermometer while it boils. Does it stay at or near to 212 degrees F? Or does the temperature fluctuate a great deal? If you can maintain a rolling boil, you should be good to go.

And, if all else fails, get yourself an induction burner and an induction capable pot and run that as your processing station. Where there is a canning will, there is always a way.

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Canning 101: The Easiest Way to Peel Tomatoes (Peaches Too!)

tomatoes in a bowl

Let’s talk about my favorite way to quickly peel tomatoes and peaches. I mention this technique a lot when I teach classes, and even wrote about it in this post in the context of peeling peaches, but as I broke down a few pounds of tomatoes today, thought it might just bear repeating.

tomatoes in a pan

Instead of bringing a big pot of water to a boil in order to blanch and peel tomatoes before turning them into a preserve, when I have a relatively small batch to peel, I do this. I trim away any soft spots, remove the cores from the tomatoes and cut them in half. Then, I arrange them cut side down in a heat proof baking dish.

tea kettle

While I’m prepping the tomatoes, I fill up my trusty tea kettle and bring it to a boil.

pouring water

When the water comes to a boil, I pour it over the tomatoes. You don’t need to fully submerge them, but you do want enough water in the pan so that it doesn’t cool down too quickly.

pan over tomatoes

Then, I slap a cookie sheet over the tomatoes to trap the heat and leave the whole thing alone for 10 or 15 minute, until the tomatoes have cooled down enough to handle.

peeled tomatoes

Drain the tomatoes and peel. The skins should slide right off and leave you with perfectly peeled tomatoes, ready to be turned into salsa or cooked down into a small batch of pizza sauce (that recipe is in Preserving by the Pint!).

peeling tomatoes

Of course, this technique really only works for smallish batches. If you’re prepping ten or more pounds of tomatoes sauce, heating up the big old blanching pot is still going to be your best bet.

What tricks do you guys have for easily prepping summer fruit for canning?

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Canning 101: How to Use a Thermometer to Achieve Set

three thermometers

We are currently smack dab in the middle of marmalade season. Though citrus is available all year round, it is both at its peak and most affordable during January, February, and March. Because of this, I’ve been getting a number of questions about marmalade making, in particular, the art of using a thermometer to determine when a batch of marmalade has reached its set point.

The reason this comes up more during marmalade season than other times of the year is that citrus is naturally high in pectin and so many marmalades can be made without the addition of any commercial pectin. The trick then becomes cooking the fruit and sugar combination to around 220 or 221 degrees F, which is known as sugar’s gel point.

When the sugar reaches that gel point, it undergoes a physical transformation and thickens. That increased thickness gives it the ability to bond with the natural pectin in the citrus and create a thick, spreadable marmalade.

thermometer probes

The issue that people are having is that they are finding a mismatch between the temperature that their thermometer is displaying and the consistency of the cooking marmalade. Typically, the marmalade appears far more cooked than the temperature on the thermometer read-out would indicate. The result is a burnt, overset preserve that is deeply frustrating, given how much work is involved in prepping a batch of marm.

There are two reasons that this can occur. One is that the thermometer is giving a faulty reading. The way you can test to determine whether your thermometer is reading accurately is to bring a saucepan of water to a boil. Once it starts rolling, insert the thermometer into the water. If you’re at sea level, it should read 212 degrees F. If you’re at higher elevations, that rolling boil will be achieved at lower temperatures. If the reading is wildly different from that which your elevation would indicate, get yourself a new thermometer.

thermometer probes with notes

The other reason that your thermometer might not be reading accurately is that is may not be be sufficiently covered with the cooking preserve. Every thermometer has a mark indicating how much the probe must be submerged in order to give a true reading. As you can see in the picture above, the three thermometers in my kitchen all need to be submerged to different depths in order to perform accurately.

If you’re making a small batch of marmalade, you sometimes run into a situation where there’s just not enough volume in the pot to fully submerge a traditional candy or deep frying thermometer (I often run into that problem with the left and center thermometers). In my case, I deal with that situation by using the Thermapen on the right or by using other methods to check my set.

Try the plate/saucer test or if it’s a truly small batch, use your eyes and ears. As it reaches the set point, marmalade will simmer more vigorously. As you stir, watch to see if it is leaving an open space for a moment after you pull your spoon through. That’s a sign of thickening as well.

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An Update on the Canning 101/New to Canning Plan

spices

Several weeks back, I wrote a post asking for feedback about my Canning 101 and New To Canning categories. It’s taken me a little bit of time to digest all the questions and figure out how to tackle them. I found that they shake out into about ten categories (though one is something of a catchall). Here’s what I’m finding that you’re interested in:

  • Canning Basics
  • Fruit Preserves
  • Pickles
  • Tomatoes
  • Sugar
  • Altitude Adjustments
  • Recipe Sourcing and Development
  • Pressure Canning
  • Using Preserves
  • Other Questions

What I’ve done is tried to pull out all the individual questions. Though I have answered many of these questions in one way or another, often those responses are buried in the middle of another post and so aren’t always easy to find. So here’s the plan. Starting next week, I’m going to start answering these questions. I probably will jump around the list a lot and will occasionally group two or three questions together if I think they are different sides of the same coin.

Some of these posts will be short and will live forever under the Canning 101 header. Others will be longer, tutorial-style posts and will get filed under the New to Canning. Hopefully, they’ll all be both useful and interesting. I’m going to use the list below as something of an index, so I will link the questions to the answers once they’re written and I may add to the list as I work.

Finally, if you have a question and don’t see it here, leave a comment and I’ll add it to the list!

Continue Reading →

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Canning 101 + The New to Canning Series

jar lifter

A big part of my mission with this website it to help teach people how to can and demystify the process. That’s why you don’t just see me posting recipes and pretty pictures. Fairly frequently, I try to get down into the nitty gritty of canning and shine some light on the hows and whys.

Over the years, I’ve created two series that have attempted to create this space for food preservation education. The first was Canning 101 (which launched in 2010 with this post), which has been my catch-all for the minutia of canning. I’ve covered everything from how to loosen stuck rings to what to do if a jar breaks in the canner under that heading (all the Canning 101 posts can be found here).

The second series was the one I started last summer, under the name New to Canning? Start Here! I wrote two posts and then promptly got lost in book edits, classes, and the height of the canning season.

I want to bring back more of these education focused posts, but I need some suggestions. What are the topics you’d like to see me cover? What are your burning questions? Is there a canning term that needs more explanation? The comment box is officially open (though really, when does it ever close. This is the internet, after all) and I want to hear from you!

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Why You Should Store Your Jars Without Their Rings

broken seal

Whenever I teach a canning class, I always mention the fact that it’s important to remove the rings from your jars before you put them away. You see, those rings are only necessary to hold the lids in place during processing and then again when you open the jar to use the contents.

There are two really good reasons why the rings should be stored separately from the jars. The first is that they last longer when they are removed, washed, dried, and stashed in a plastic bag (they have a tendency to rust if not stored properly).

The second reason is that if the contents of the jar happen to spoil (though it happens rarely, it does happen), you’ll know more immediately. That’s because when things spoil, it typically happens because there’s some sort of bacterial growth that off-gasses. That creates pressure which eventually breaks the seal.

a jar that broke its seal

The reason I’m writing about this topic today? It’s because this tip that I’ve shared so many times in canning classes actually proved useful in my own canning life yesterday. I was in my hall coat closet (one of the spaces that doubles as my pantry in this small apartment of mine) to get some whole peeled tomatoes. I picked up the jar and the lid slid right off onto the flour.

I stared at it for a moment, unbelieving that one of my precious jars had gone bad, but then felt so grateful to have followed my own advice. If the ring had been on the jar, I truly might not have known that the seal was no good. I walked those tomatoes over to the garbage disposal and sent them on to a watery grave (they actually smelled fine, but I take no chances).

So, if you’re storing your jars with the rings still on, do yourself a favor and go pull them off. Your future self may thank you.

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