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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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Canning 101: Understanding Acid and pH in Boiling Water Bath Canning

pickles on a table

Today’s post is inspired by a rash of questions I’ve gotten recently in regard to my recipe for Honey-Sweetened Peach Vanilla Jam. A number of you are concerned because while that recipe contents lemon zest, it doesn’t contain any lemon juice. That jam is safe as written, but we need to dig a little deeper into canning science to understand why. Read on!¬†

If you’ve been canning for any length of time, you’ve probably heard mention of acid levels in relation to safe boiling water bath canning. Anything that is preserved in a boiling water bath must have a high acid content. The reason that high acid levels are important is that the presence of acid inhibits the germination of botulism spores into the botulism toxin. Botulism spores can only develop into the botulism toxin in low acid, oxygen-free environments.

When you preserve something in a boiling water bath canner, you heat the jars and their contents to the boiling point (that temperature varies depending on your elevation, but at sea level the boiling point is 212 degrees F). That heat is enough to kill off the micro-organisms that can cause spoilage, mold, or fermentation, but it’s not enough to kill botulism spores (they require far higher temperatures). The process of boiling the jars also helps to drive the oxygen out of the jars, creating a vacuum seal. For jars that have sufficient acid content, the result is a jar of food that is safely preserved and shelf stable.

The way food scientists (and home canners) determine whether something is high or low in acid is by pH. If something has a pH of 4.6 or below, it is deemed high in acid and is safe for boiling water bath canning. If the pH is 4.7 or above, it is considered low in acid. We’ll talk more about how to preserve those foods that are low in acid and have a pH of 4.7 or above another day, but to give you just a hint, that’s often where a pressure canner comes in.

If a food is close to the 4.6 pH point, you can often add enough acid to bring that product into the necessary safe zone.¬†Fruits like tomatoes, figs, asian pears, melons, persimmons, papaya, white peaches and white nectarines, and bananas are often just a bit too low in acid in their natural state for safe canning. So in order to lower the pH to a safe level, we add either bottled lemon or lime juice, or powdered citric acid to products featuring those ingredients. Once the acid levels are high enough to inhibit the botulism spore’s ability to germinate into a deadly toxin, that product is safe for boiling water bath canning.

However, there are a world of foods out that naturally have a pH that is well within the zone for safe preservation in a boiling water bath canner. Here’s where we come around to the peach jam I mentioned in the introduction to this post. That recipe specifically calls for yellow peaches, which typically have a pH of 3.4 to 3.6. I know the general pH range for yellow peaches because the FDA provides a handy reference page on their website that lists the general pH range of most common fruits and vegetables.

You could certainly add lemon juice to my jam in order to balance the flavor and add a little extra pectin (citrus fruit is naturally high in pectin), but it’s not necessary for safety.

Updated to add: One last thing! It’s important to remember the pH of the entire jar counts here. This is why it’s so vital to follow tested, reliable recipes for things like tomato sauce or salsa. Sure, you can add bottled lemon juice to your tomatoes to lower the pH, but if you’ve also added onions, garlic, and basil to your sauce, you’re not just balancing the acid of the tomatoes, you’re also taking the rest of the ingredients into account. That’s why salsa recipes designed for canning contain so much bottled lemon or lime juice, or vinegar.

 

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Canning 101: How to Substitute Pectin

pectin containers

During the time I was writing my first cookbook, I was something of a liquid pectin fan girl. I liked its ability to create a natural, not-too-firm set. However, as time has gone by, I’ve become more of an equal opportunity pectin user. I regularly use regular powdered pectin, Pomona’s Pectin, and even sometimes boost the set of my jams with some grated apple or ground lemon peel. I also make preserves without any additional pectin at all (thanks to the size of the batches, there’s not a drop of extra pectin at all in the next book).

I get a couple of pectin questions a lot. The first is, how do you choose the kind of pectin you use in each recipe? Unfortunately, I don’t have a really great answer for that one. I typically just reach for whatever’s closest in the kitchen. There’s no true formula. I do tend to use powdered pectin when I’m working with lower pectin fruits, but if there’s no powdered pectin around that day, I reach for the liquid. If I don’t have either kind of traditional pectin, I’ll use a splash of calcium water and a little bit of pectin from a box of Pomona’s Pectin.

The second thing I’m frequently asked is, how do you swap powdered pectin for liquid? Happily, I have a more concrete answer for this one. You use two tablespoons of powdered regular pectin for every packet of liquid pectin. The difference in usage is that instead of adding the pectin at the end of cooking like you do with liquid, you whisk the powdered pectin into the sugar before you combine it with the fruit. It responds better when you cook it the entire time and you avoid the risk of pectin clumping that can appear if you try and add powdered pectin at the end of cooking.

I’ve not come up yet with a perfect formula for converting full sugar recipes to lower sugar ones that use Pomona’s Pectin. The only tip I have about that pectin is that I always use about half as much as the recipes in the packet call for. I find that if you follow their instructions, you end up with a VERY firmly set jam. As someone who prefers a softer set, I find that using half as much gives me a satisfying outcome.

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