can, freeze, or dry? home food preservation basics, with elizabeth andress

Tomato sauce in freezer jarsPERHAPS YOU’RE SCANNING the seed catalogs, imagining tasting that first sweet ‘Sugar Snap’ peapod, or (finally!) a ripe garden tomato—both worthy goals. But don’t forget to think a little farther ahead. As important as having the right seeds and seed-starting gear ready is having the right food-preservation equipment ready to process your homegrown treasures at the other end.  Are you ready for stashing the coming harvests?

Dr. Elizabeth Andress, is a Professor and Extension Food Safety Specialist at the University of Georgia, and oversees my go-to reference website about all matters of putting up food sanely and safely: It’s called The National Center for Home Food Preservation

We hope to inspire you to plant extra and make this the year you enjoy the fruits of your garden labors all through the offseason–whether canned or dried or frozen. Read along as you listen to the Feb. 27, 2107 edition of my public-radio show and podcast using the player below. You can subscribe to all future editions on iTunes or Stitcher (and browse my archive of podcasts here).

getting ready to preserve the harvest, with dr. elizabeth andress



Q. First: I mean what I say about that website. Every time someone asks me a question, I am always making sure to check it with “you.” [Laughter.]

A. I appreciate hearing that.

Q. A giant thank for that. Those little links in the sidebar of the website—I am always looking there, because it’s so simple: It says, “How Do I” and then (click) can, or freeze, or dry, or cure and smoke, or ferment, or pickle, or make jam and jelly—and it even has information about how long I can store vegetables I have harvested, like root crops, and how to store fruit best and so forth.

There are various tactics for preserving food, Elizabeth, and each has pluses and minuses. Can we do a quick overview of whether to can, freeze, or dry…maybe you could start there, and help us?

A. You’ve just named the most popular and common ways that people do preserve food at home—that being canning, freezing or dehydrating. There are ways that you can ferment food and do some curing to prolong their shelf life, but they are not always used in ways that refer to longterm preservation, like canning and freezing and drying might. But those are the most popular ones; the main three.

Each has their pluses and minuses, for people making decisions. Some foods, for example, may not freeze well. Those that are particularly high in water content have a lot of damage caused by that water turning to ice crystals, so things like lettuces and other fragile greens, or celery, come to mind as things that don’t produce a very nice frozen product.

When we come to canning, of course, because there are more safety concerns when the foods are going to be stored in the closed jars at room temperature that there might be at a frozen temperature, we have to also consider what we actually safe, recommend processes for canning to help out there. So there are some foods that we might not be able to recommend canning, simply because the research hasn’t been done to know what the safe process is.

Q. And with the drying—sorry, dehydrating? [Laughter.] I always use the informal word.

A. That’s OK; I do, too.

Drying of course has some of the same concerns that freezing might. It would make sense that maybe you can dry anything if you remove the water from it, and that’s true. There are just some foods that don’t produce a very nice dried-food product—so it might not be particularly recommended that you do that.

One other thing to think about with drying at home is that you might need to remove a good bit of the moisture and get them particularly drier than you might see with some commercially dried foods for longterm storage. That’s because sometimes some other hurdles to bacterial or mold growth are given in commercial products that we don’t recommend at home, so the recommendations at home might be to get to a little bit drier texture.

I’m trying to think of some of the things that would not be good to dry—like pomegranate is not recommended for drying, but that might seem like a no-brainer to anybody.

Q. [Laughter.]

A. Avocados don’t preserve very well in drying—but neither do they in freezing or canning. So there are just limitations on certain kinds of foods.

Q. If I haven’t canned before—and I should say I used to can all the time, for many years, and I have moved gradually toward freezing more—but if I haven’t canned before, must I invest in a pressure canner? Or can I start with a boiling-water bath, with lees capital investment, so to speak?

A. Boiling-water canning would of course be less of an investment, because you can get a less-expensive boiling-water canner. You don’t have to invest in a pressure canner, as long as you are willing to accept the limits if what can be done without pressure.

For example, you can’t can meat, poultry, seafood or vegetables (without pickling them, at least) without a pressure canner.

But if someone is starting out, like you suggested, I usually recommend they definitely do start with a boiling-water-canned food. It lets you first of all have fewer safety concerns should something go wrong when you store it on the shelf, but it also to me lets someone get familiar with all the steps in canning: getting your food prepared, getting it into the jars while it’s still hot, getting the lids put on right, getting them into the canner. It lets you go through the practice of those steps without having even some additional steps that have to be managed while you are pressure-canning. So that’s the less complicated form of canning. It’s also a little bit safer for many of the foods that are boiling-water canned. [More on using a boiling-water canner.]

Q. So tomatoes, for instance, I could do either way if I make sure the acid is correct in them, correct?

A. If you want to can tomatoes in what I’d call plain forms, there are several options: tomato juice, crushed tomatoes, whole or half tomatoes packed in water. The research-based recommendation we have for canning those do allow for boiling-water canning, as long as you do add a minimal amount of acid to each jar. That’s simply because people have historically have been used to canning tomatoes in boiling water, and then we started to learn a few decades ago that some of the varieties of tomatoes were coming in with lower natural acidity than would allow for boiling-water canning.

So the research was actually done in the 70s, that came up with the recommended amounts of acidification, that allowed people to still boiling-water can tomatoes. Back at that time, people we perhaps more afraid of pressure canners than we are noticing today, but it also meant just a little bit of acid had to be added to allow you to do that. And it’s also a lot less time involvement and heat involvement to do them in the boiling-water canner. [More on canning tomatoes and tomato products.]

Q. And I should have clarified: When we say “pressure canner,” and that it’s an investment, I don’t mean a multi-purpose electric cooker, or even a pressure cooker, either, do I?

A. Let me put it this way: To use our USDA research-based processes for pressure canning, you do need to use a pressure canner that is of a certain size, first of all. Now they might be sold as something called a cooker/canner, but you do need to make sure it’s recommended for canning. If something is much smaller, like a small pressure cooker only, then it probably doesn’t provide enough sterilization value for the processes that were tested in the larger units. So that’s why we caution about canners.

You brought up the issue of electric canners, or what are being sold now as multi-cookers with a canning function. Unfortunately, I can’t recommend that the USDA processes be used in those, because there is enough about the situation with how the appliance operates that we don’t have answers for. We know it differs from canning in a traditional canner. So if someone wants to use them, they have to be willing to trust the manufacturer’s advice, but I can’t support the use of our processes in those right now.

Q. And I have to say: better safe than sorry. And as I said at the beginning of the show, I love coming to the website for the National Center for Home Food Preservation, getting the specific USDA-approved guidelines. I want to know the right way, and I don’t want to fool around because there is health and safety involved. [Get the USDA canning guidelines.]

A. And of course that is the approach we like, too. There is lots of anecdotal evidence from individuals, and anybody can find it on the internet, where people are taking a chance and making up their recommendations for their own recipes, and I guess I like to think like you think: I’m not willing to take that chance with my health or my family’s health.

Q. Well, Margaret and Elizabeth say: Just say no to wacky adaptation to canning recipes and processes. [Laughter.] Now that we know we are both conservative…

I forgot to ask: The different methods, whether dehydrating or freezing or canning, do they have different nutritional results? Are there pros and cons that way about choosing a method. I always think of freezing as a way to preserve a lot of nutrients, assuming the thing holds up in the freezer.

A. And that is the appropriate assessment to make at this time. We actually don’t have a lot of documented nutritional value of home-preserved foods, and especially not since the 1970s, when some of that was done also.

But it is well-established with research—with all kinds of food-processing research—that says if you use freshly harvested, good-quality produce, and get it frozen using good methods and good packaging, that freezing will help you retain the best nutrient profile.

Even if you blanch some vegetables, it’s a lot less heat treatment than canning, and with many of our vitamins in particular, their activity is broken down or changed by heat. So we have lower vitamin activity in some canned foods over frozen.

Drying I have a little bit less evidence for, but of course it is a longer exposure to heat than freezing, even though it is for a lower temperature. It’s being heated in the open air and that can be a little bit detrimental to some of our major vitamins, like Vitamin C in particular again.

Q. I said at the beginning that it’s not just time for gardeners to get their seed-starting gear together, but also to get their canning gear together. If we think of canning, and I reuse jars, lids, rings, etc.–what can be reused and what am I looking for to tune up my equipment?

A. Let’s start with jars: Canning jars of course can definitely be reused, as long as they are in good condition. You should always get out your jars before you are ready to use them, and make sure you don’t have any nicks or cracks in particular around that sealing surface that has to mesh with your gasket on your lid.

And just observe the rest of it. If you happen to see some marks on the glass that might indicate that metal spoons or knives have put little nicks in there, you might not want to use those. I hate to have people go to all the trouble and then find the jar falls apart in the canner, because of some of that stress from utensils being used in it.

This is actually a good time of year for many people because particularly in the Southeast or warmer areas of the country, because we will start thinking about having produce come in here in just a couple of months.

Q. Are you trying to make me jealous? [Laughter.]

A. I’m sorry. Actually I am wondering what is going to happen this year, because we have had an extremely warm winter so far. We’re already getting pollen counts [note: show was recorded February 9, 2017], and that blows my mind.

In any case: Do check that. If you use a jar that has the flat metal lid and ring band, ring bands can be reused as long as they are in good condition—not bent out of shape or rusty, that might interfere with them holding down the lid and screwing into place correctly. We do recommend with the flat metal lid, even though I happen to note people try to push them and reuse them and might have success, that the chances of a good seal the second time are much lower. So we don’t want people to waste their time and effort and then not have a seal form, so we recommend a new flat lid every time—as well as the manufacturers of those that do also.

So then with the boiling-water canner can really be any large-enough stockpot that also has a rack in the bottom, and the lid, to make sure you keep it boiling. They are made like that, and I know that some people have made their own by using a large stockpot, and you can buy cake-cooling racks in many sizes and they fashion their own rack. The rack is important so you don’t have that direct heat contact from the metal bottom of your canner to the jar, to prevent breakage.

Something else people don’t realize is that that little bit of elevation and the openings in that rack are important to the heat transfer around the jars during processing. So that’s a little bit of a safety factor there.

Q. One thing I learned the hard way, when I moved from a house that had a gas stove to one that had a cooktop glass top electric stoves, was that my old canning pot—an enamelware grayish-colored one—had a corrugated bottom and didn’t make proper contact with the electric cooktop. It has to be perfectly flat, or you won’t be able to get to a full, continuous boil.

A. That’s a good point, and the reason I was explaining that some people started making their own was that it happened with the advent of the smooth-top stoves. But of course now there are a couple of manufacturers that sell flat-bottomed boiling-water canner. If you are going to fashion your own, you have to make sure it’s also a flat-bottomed stock pot.

They should also be big enough that the water always stays a couple of inches over the tops of your jars during the processing time.

Q. Every year I say I am going to invest in a dehydrator, and then I get hung up on whether to go for the deluxe one or the more economical one, and what features matter. Can you walk me though how to shop for the right features in a food dehydrator?

A. There are many prices and a wide variety of features out there. To get the best-quality dried food also, we recommend that you get something that has a thermostat on it, and not just and an on and off switch. The best temperature for most drying is 140F, but I’d look for a thermostat from 85F to 160F, for a lot of the directions you see.

Think about there being a good fan system, because you want good air circulation in there also. Look at the manufacturer’s information about the kind of ventilation and airflow that’s provided.

There are two basic kinds: Some will have what we call vertical airflow, and the motor will be either in the bottom or the lid, to circulate the air up and down throughout. Another type has what’s called horizontal airflow, and is more like a cabinet—a square cabinet—and the air flows from the back. Again, you can think of plusses and minuses for that, and we have it spelled out on our website, too.

Definitely if it’s electric, look for UL seal of approval. Some of them have timers—that’s not really necessary, as long as you are going to be available to check the food near the end of the drying period and remove it. Drying does require a little more attention near the end, to make sure you don’t get things over-dried, or under-dried. You need to monitor.

The one thing I do like now about some of these vertical flow units, is that they are putting the motors and fans in the lids, and I would consider that a plus. Foods might drip some and drop as they dry, down to the bottom, and it was always a little harder to wash out the bottom of an electric dehydrator—you couldn’t submerge it. That’s very helpful to me, that they put it in the lid.

Q. Frankly I used to use my oven on like 250 degrees or “warm” to dry tomatoes—and speaking of them and dried foods in general: Scary things that readers tell me, about how they “preserve” tomatoes after drying them, by putting them in a jar of olive oil and store them. I’m like, “No, no!” That’s not safe, but where should we store these dried fruits or vegetables?

A. Vegetables (compared to fruits) are a little bit easier to deal with, when you try to determine doneness. They should actually be dried until they are pretty brittle, and some the smaller ones like corn kernels and lima beans should actually shatter if you hit them with a hammer. [More on how dry to dry fruits and vegetables.]

We of course like to leave fruit products, which would include tomatoes, a little bit moister and more flexible, because we can eat them in that form. But then you want to make sure there is not too much moisture that would promote molding or other spoilage, so we do recommend you put them in a close container—an airtight container—and watch them for the first day or two to make sure there is not moisture condensing. If so, then they would need to be re-dried some.

But once you get things dry enough, keep them for best quality in as dark a spot as possible, and airtight and as oxygen-free as possible. The airtight part has to do with not letting moisture in, also—you don’t want them to reabsorb humidity out of the air, which they would do. [More on how to store dried foods.]

Q. I said we’d have time to talk about freezing, which I am totally obsessed with, and I sometimes think why bother to do anything but freeze. With freezing, you can do a small batch, or if you have leftover something—like a big thing of soup—you can freeze half of it. Is freezing the idea place for longterm storage?

A. “Ideal” would kind of depend what the food was, but you have mentioned some of the benefits to me of freezing also. I mentioned earlier that there are some recipes and foods we can’t really recommend canning, because we don’t know the safe process. We don’t have that concern with something put in the freezer.

As long as it’s kept that cold, there is no microbial activity. So it is a good thing to do with your own recipes. Batch cooking, as you said—you might make a meal that you eat once then freeze the extra, to have ready to defrost or reheat later. Smaller quantities will work well.

Packaging materials should also, however, be a good quality, that doesn’t allow air transmission either through the sealing area or the sides of the container—like with bags, look for “freezer” ones and not “storage” ones. If you have a container with a lid, make sure it fits really tight against the bottom sealing areas.

Q. I will add that I freeze in my former canning jars—especially my straight-sided ones.

A. I agree.

preserving references from the center

THE NATIONAL CENTER for Home Food Preservation has a series of “How do I?”reference sections:

PLUS, the Center website has among its many other assets these dowloadable reference guides:

prefer the podcast version of the show?

MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its seventh year in March 2016. In 2016, the show won three silver medals for excellence from the Garden Writers Association. It’s produced at Robin Hood Radio, the smallest NPR station in the nation. Listen locally in the Hudson Valley (NY)-Berkshires (MA)-Litchfield Hills (CT) Mondays at 8:30 AM Eastern, rerun at 8:30 Saturdays. Or play the Feb. 27, 2017 show right here. You can subscribe to all future editions on iTunes or Stitcher (and browse my archive of podcasts here).

  1. Pam says:

    Hi Margaret,
    In the Pacific Northwest we use canning jars on a daily basis. Plastic is a no-no. I bring my salad for lunch in a glass jar. Vintage jars are my favorite.

    Just yesterday I made a pot of homemade chicken and dumplings. The recipe called for thyme. Perfect. I took my Ziploc bag of frozen thyme out of the freezer, gave it a brisk shake and scooped out a heart teaspoon full. I prefer to freeze most of my harvest (cubed butternut squash, beets, green beans, tomatoes and herbs).

  2. Tibs says:

    When the power goes off or someone leaves the freezer door ajar or your spouse decides to get a quarter beef, canning is better. I have made a delish tomato soup for years and used boiling waterbath method and probably should change my preservation method. It has onions, celery, cornstarch, and butter. Am i furtunate that i haven’t killed us all?

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