Q. I made a beef stew in a 350°F oven. That’s hotter than a water bath, so why can’t I just can the stew as is? Why [...]]]> Ask the Goats is a (mostly) weekly feature in which we, the goats, attempt to answer your food preservation questions. Got a question? Drop us a line at dorisandjilly@gmail.com.

Q. I made a beef stew in a 350°F oven. That’s hotter than a water bath, so why can’t I just can the stew as is? Why do I need a pressure canner?—anon (to me, anyway) via Kaela at Local Kitchen

A. This is a great question, just at that point where common sense bumps up against the laws of physics. We say, over and over again, that the heat of a water-bath canner is not sufficient to kill off the kinds of nasties (botulism, I’m looking at you) that can live in low-acid, anerobic environments (i.e., beef stew). But, obviously, a 350°F oven is much hotter than the 212°F of boiling water. So, what’s the problem?

The problem has to do with what’s inside the stew pot. When an oven thermometer reads 350°F, that means that the air temperature is 350°F. Your stew, on the other hand, is going to be hovering at its boiling point. This is a consequence of what’s called the Phase Change Law, which says (more or less), that a substance will maintain the temperature at which it changes phase until the phase change is complete. Water melts at 32°F, and it boils at 212°F. If you put a pot of boiling water in the oven, it’s not going to get above 212°F until all of the water has turned to steam. Then, and only then, can the temperature start increasing.

Now, in beef stew, you’ve got a liquid that, depending on what it has in it (water, wine, stock, etc.) is boiling probably somewhere between 190°F and 212°F. But you’ve also got solids that are probably at a lower temperature. Think of what happens when you put a large roast in the oven. You might cook it for hours, and it might still be at 150°F. All of which is to say that your beef stew is nowhere near 240°F.

But how does the pressure canner do it? Well, when I said that a substance that’s changing phase will maintain an even temperature, that’s not quite true. It will maintain an even temperature under conditions of constant volume and pressure. Crank up the pressure, and the temperature goes up. And hence, safe canning conditions for low acid foods.

Want more canning advice? Check out the liveblogging stream from the panel on canning, preserving, and foraging that I participated in with Marisa from Food in Jars, Hank from Hunter Angler Gardener Cook, and Sean from Punk Domestics at last weekend’s BlogHerFood conference in San Francisco. I had a blast, and I hope those in attendance found it as informative as I did entertaining.

Q. Hi. I am not new to canning. But something happened this year that has never happened before. [...]]]> Ask the Goats is a weekly series in which we attempt to answer your questions about growing, making, eating, and preserving food. Got a question for the goats? Drop us a line at dorisandjilly@gmail.com.

Q. Hi. I am not new to canning. But something happened this year that has never happened before. I canned 16 quarts of vegetable soup. I used the water bath method and processed them for 1 hour. I checked the seals and they were good. One week later the lids started pinging. What went wrong? That was an awful lot of work to throw away. I am very disgusted. P.S. My salsa, peach preserves, strawberry jam are all sealed and delicious.—Mary

A. Alas, Mary, vegetable broth is a low-acid food, and therefore not safe for water-bath canning. For the purposes of canning, all foods are either high-acid or low-acid foods. The kinds of food-born pathogens that can live in a high-acid environment can be killed fairly easily with moderate heat, so you can process them in a boiling water bath. Low-acid foods, on the other hand, can harbor botulism spores that are not destroyed at 212°F. Low-acid foods must be processed in a steam pressure canner that can reach much higher temperatures (usually 240ºF).

Remember, only fruits (excluding tomatoes, figs, green mangoes, and white peaches) and certain kinds of fermented pickles are acidic enough for water-bath canning without adding acid. For everything else, you have to either acid—sometimes in substantial quantities—or use a pressure canner.

Pressure can vegetable stock just as you would chicken stock (for step-by-step directions, click here). The Ball Blue Book recommends 35 minutes for quarts at 10 pounds pressure. If you don’t have a pressure canner, you’ve got to freeze it.

In happier news, the winner of the Put ‘Em Up! giveaway is Amanda Nelson, who’s new to canning and expecting twins! I think your strategy to put up as many nibble-ables as possible is an excellent strategy.

The most important thing to consider when you’re canning is whether your item is a high-acid or low-acid food. Most food-born pathogens, including yeasts, molds, and most bacteria, can be killed at 212°F. [...]]]>
Yes, yes, yes, I know. The tomato can jam entries should be posted next week, not this. Consider this post a safety intervention.

The most important thing to consider when you’re canning is whether your item is a high-acid or low-acid food. Most food-born pathogens, including yeasts, molds, and most bacteria, can be killed at 212°F. Botulism, on the other hand, that nasty, invisible, food-borne pathogen we’ve all heard so much about, can survive up to somewhere around 238°F. (It’s actually the spores that can survive, but never mind that). But because botulism can’t grow in a high-acid environment, you can still can high-acid foods in a water-bath canner that will never get about 212°F. For low-acid foods, you need the additional heat of a pressure canner, which can take you up to 240°F at 10 pounds of pressure at sea-level. Let me repeat: you can’t get botulism from high-acid foods.

With me so far? Good.

Here’s the thing. Tomatoes aren’t quite a high-acid food. They’re borderline. Older varieties, many heirloom varieties, and most of the varieties that you’re likely to grow at home, frequently are. Newer varieties—particularly the kinds of tomatoes that you tend to find in grocery stores—aren’t necessarily acidic enough. It’s therefore recommended that you add 1 T of lemon juice per pint jar, or 2 T per quart jar, of tomatoes to make them safe for water-bath canning. If you don’t like lemony tomatoes, you can always pressure can them.

Which brings us back to sauce. I’ve seen many, many recipes over the years that say that you can can tomato sauce in a water-bath canner. Many of these are in reputable books that I trust, like Anna Thomas’s The New Vegetarian Epicure. But let’s think about this for a minute. Here you are, taking tomatoes, already a low-acid food. You’re adding olive oil, probably some onions, maybe some garlic, and a handful of herbs. All of these things are low-acid foods. With each one, you’re raising the pH (lowering the acidity) of your product. The more experienced I get in my own canning, the more and more queasy I am about all the people who are going to excitedly put up jars and jars of tomato sauce in a water-bath canner this summer.

The Ball Blue Book does include a version of tomato sauce safe for water-bath canning, but it contains 1 T lemon juice per pint jar and a processing time of 35 minutes (for pints). I can only conclude that if you’re not adding something more acidic than tomatoes (like lemon juice or vinegar) to your sauce, it’s probably not safe for water-bath canning, and certainly not at the 20 minutes usually recommended in non-canning cookbooks. Ergo, you might want to try pressure canning it.

Here’s one version of a meatless tomato sauce appropriate for pressure canning, using the processing times recommended by the National Center for Home Food Preservation.

Canned Tomato Sauce

10 pounds tomatoes, peeled, cored and roughly chopped
1 large onion, chopped
6 cloves garlic, minced
1/4 c. olive oil
A big handful of basil—about a cup or so—chopped
Salt to taste (I use about 1 T kosher)

1) Heat the oil is a large, wide stockpot. The wider the stockpot, the faster your sauce will cook. Sauté the onions and the garlic in the oil until they’re translucent.

2) Add the remaining ingredients and bring to a rapid boil. Turn the heat down to medium and cook until the sauce has reduced by about half. This may take several hours, depending on your stove and your pot. If you want, you can run the sauce through a food mill at some point, but I find that if you cook it long enough, the tomatoes break down on their own.

3) Meanwhile, prepare 4 to 6 pint jars (and maybe a half-pint just in case) and an equal number of lids. Transfer the hot sauce to clean jars and adjust two-piece lids. Process pints for 20 minutes, quarts for 25 minutes at 10 pounds pressure in a steam-pressure canner.

For step-by-step instructions on pressure-canning, please see this post. Please note: I find I get a better seal, and am less likely to lose the contents of my jars, if I wait a long, long time after the pressure’s dropped before opening the lid. Like, hours.

When you first asked me this, I thought it was an easy question. So easy, in fact, that I planned on conducting a little kitchen experiment to document both the reaction and its counter-reaction. But things didn’t work out that way, [...]]]> Sometimes garlic turns blue when I cook it. Why? Is it safe to eat?

(Andrew, Philadelphia)

When you first asked me this, I thought it was an easy question. So easy, in fact, that I planned on conducting a little kitchen experiment to document both the reaction and its counter-reaction. But things didn’t work out that way, as I’ll explain below. But first, let’s answer your question. The simplest answer is that garlic contains a set of pigments known as anthocyanins. Under certain conditions, the anthocyanins appear blue-green. They are harmless to eat, and may even go away depending on what you do to the dish next. Harold McGee explained his take on this in his inaugural “Curious Cook” column in the New York Times:

I hear every year from cooks who have been alarmed at seeing normally pale garlic turn bright green and even blue, sometimes when the cloves are pickled whole, sometimes when they’re chopped and cooked with other ingredients. I’d often been puzzled by little blue-green specks when I made garlic bread with loaves of sourdough, but I was really rattled the first time I puréed raw garlic, onion and ginger together in a blender to make chicken in yogurt from Madhur Jaffrey’s “Invitation to Indian Cooking.” When I fried the purée the entire mass turned turquoise blue.

I asked a couple of Indian friends who happen to be plant biologists whether they knew what was going on. They said they had never seen the blue purée, because Indian cooks don’t grind onions and garlic together. They grind or chop them separately and usually fry the onions first. . . .

According to chemists at the China Agricultural University in Beijing, aging the garlic gives it a chance to accumulate large quantities of one of the chemicals that generate the color; fresh garlic doesn’t green much at all. And a strong green color develops in Laba garlic only with acetic acid, the main acid in vinegar (also found in sourdough), because it’s especially effective at breaching internal membranes and mixing the cell chemicals that react together to create the green pigment. The pigment itself turns out to be a close chemical relative of chlorophyll, which gives all green leaves their color.

Two recent reports from the House Foods Corporation in Japan detail exactly how the garlic and garlic-onion pigments develop. Their creators are the same handful of sulfur compounds and enzymes that give the allium family its unique pungent flavors. Under the right conditions these chemicals react with each other and with common amino acids to make pyrroles, clusters of carbon-nitrogen rings. These rings can be linked together into multipyrrole molecules.

The ring structures absorb particular wavelengths of light, and thus appear colored. The two-pyrrole molecule looks red, the three-pyrrole molecule looks blue and the four-pyrrole molecule looks green, as does its cousin tetrapyrrole, the chlorophyll molecule. Like chlorophyll, all the pyrrole pigments are perfectly safe to eat.

Now, I was familiar with the explanation that says that the blue-green apparance is more likely to take place in acid environments. In my own experience I noted that garlic only tends to turn blue when cooked in lemon juice, usually in a metal pan. In fact, the anthocyanin/acid relationship is so strong that you can actually use some vegetables—the classic is red cabbage—as a home pH meter. (You can learn more about the chemistry of red cabbage color changes in this episode of Distillations, a chemistry podcast.)

It was with all of this in mind that I had what I thought was a brilliant idea. If acid turns garlic blue, shouldn’t baking soda, a base, turn it back? So for you, dear readers, I attempted to conduct a scientific experiment.

First I added lemon juice to minced garlic in a glass bowl. Nothing happened.
I transferred the contents to a metal pan. Nothing happened.
I heated it up, thinking maybe the reaction needed a jump start. Still nothing happened.
I added white vinegar, thinking maybe my lemons weren’t strong enough. Nothing happened.
We ate dinner, giving the garlic and acid time to get to know each other. Still no blue.

At this point, I did some additional research and learned that garlic actually turns blue for two reasons. Certainly the anthocyanins are the main culprit. But garlic also contains a lot of sulfate that, when combined with copper, creates copper sulfate, an insoluble, bright turquoise compound. (Again: still fine to eat.) Apparently the trace amounts of copper in water and other foods can be enough to trigger the reaction.

So, I added water. Still no blue.

More research: what food stuffs have high proportions of copper, I wondered? Leafy green vegetables, like kale, chard, and spinach, and certain nuts, like sesame seeds.

I dumped a big pile of sesame seeds into the pot and kept cooking. At this point the kitchen smelled terrible. But still no blue.
Table salt, perhaps, with its iodine content? No go.

This went on and on for about an hour before I finally gave up. So while I can certainly tell you what turns garlic blue, I cannot tell you whether you can turn it back by adding baking soda. If it happens to you, give it a try, and let me know.