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HOMEGROWN Life: How to Can Safely

HOMEGROWN-LIFE-LT-GREENHere in the Bay Area, we just planted our tomatoes, eggplants, and tomatillos last weekend. In a couple more weeks, we’ll be planting peppers, squash, cucumbers, melons, beans, and corn. And in just a few months, we’ll be busy harvesting and preserving our bounty through drying, freezing, and canning.

Thinking ahead to our own canning made me think about how preserving has gained in popularity in recent years, and how I’ve see some really great recipes out there on the interwebs. I’ve also seen some packed in jarsreally dangerous ones that scare me. I’ve seen so many bad ones, in fact, that I’ve decided I’m not going to judge canned goods at events anymore unless the recipe and canning process are included along with the sample. You can’t simply shoot from the hip and make up recipes that “sound about right” and expect them to store at room temperature for extended lengths of time. There’s a science behind canning to ensure safety that I can’t stress enough.

So, I figured that with our canning season fast approaching, and already here in many other parts of the country, we should discuss some guidelines on how to can safely.

The Rules

1. Just because a recipe is on the Internet doesn’t make it safe.

Be critical of every recipe you see on the Internet. If it’s not pressure canned, check to make sure it has enough acid, is processed long enough, and uses low-acid ingredients, especially if it is raw packed. If it’s high acid, make sure it is water-bath canned long enough. The USDA has safe canning guidelines on its National Center for Home Food Preservation site that you can use as a cross-reference. Avoid any recipes that have dairy, eggs, and pureed low-acid food (such as lemon curd, pumpkin butter, and pureed bananas) and don’t instruct you to keep the finished product in the refrigerator for a limited amount of time (usually a month) or to freeze it.

2. Books are *usually* a safe bet.

I say “usually” because I’ve seen some questionable and downright dangerous recipes published in books. Check the book to make sure it says the recipes have been tested for safety. The most reliably safe books (though I can’t testify to the tastiness of all the recipes in these books):

Ball Complete Book of Home Preserving
Canning for a New Generation: Bold, Fresh Flavors for the Modern Pantry
Put ’em Up!
Food in Jars: Preserving in Small Batches Year-Round
Complete Guide to Home Canning and Preserving
(2009 revision)


These refrigerator-style pickles have a finite shelf life.

3. If you find a safe recipe, do not alter it—but if you alter it anyway, know the guidelines.

Even adding a bit more onion to a recipe can alter the pH enough to make it unsafe. For water-bath-canned products, you want the pH to be 4.6 or lower. Unless you have a superdeluxe Vitamix blender, however, chances are simply blending and using a litmus strip isn’t going to give you an accurate reading of the acidity. The safest way to test an item’s pH is to send it to a food lab, but that can get expensive—so, just stick with a tested recipe, wouldja? If you can’t help yourself and you do change the recipe, always follow the basic safety guidelines. If you’re not sure, err on the side of caution and don’t alter it. The canning recipes I have on my blog always follow the safety guidelines, and I almost always increase the acid, even when I don’t need to, just to be on the safe side. I will not post low-acid recipes that require pressure canning. Recipes that don’t follow the safety guidelines, like our oven-baked heirloom tomato sauce, are always for eating immediately or for freezing (which is why we don’t include canning instructions with it).

4. Not all fruit is created equal.

While many fruits are high in acid and relatively easy to can, some are either borderline or low acid and must have acid added. Figs, bananas, white peaches, Asian pears, watermelon, mangoes, and tomatoes all fall into the category of not acidic enough to can on their own without adding acid. Be sure to follow the USDA guidelines when canning these items. I have posted tomato-canning guidelines that are based on the USDA guidelines and the Ball Complete Book of Home Preserving.

5. If it’s a low-acid food and you don’t add acid, don’t even think of water-bath canning it. Same goes for recipes with meat in them, even if you add acid.

I’m serious here. Botulism will kill you dead. And adding loads of salt or sugar won’t save you.

6. If a recipe says to pack pint jars, don’t pack quart jars and increase the time to what you think it should be.

Sometimes you’ll come across recipes that only give you the processing time for a specific jar size. Don’t simply pack your product into larger jars; you don’t know what the processing time is for them to be safe. Tomato paste is a good example of this. Due to its consistency, it’s best canned only in 8 oz jars. Never can using jars larger than a quart unless the recipe calls for them. (Tomato juice can be canned in 1.5 L jars, per the Ball Complete Book of Home Preserving.)

7. Don’t take shortcuts.

  • Cut fruits or vegetables into your recipe’s indicated size, as this ensures that the center of the food reaches the correct temperature (and acidity, if using low-acid foods).
  • Don’t “eyeball” the amounts of your ingredients. Think of this as a science experiment rather than an art project.
  • If using a water-bath canner, start your processing time after the water has come back up to boiling or after you reach pressure when pressure canning.
  • Pack hot food into hot jars that were slowly brought up to temperature, not directly into cold jars. (A sudden heat change caused by hot food will stress the glass, causing breakage.)
  • Don’t reuse lids, except for Tattler lids. You can reuse rings, though.
  • Follow your recipe’s head space rules. Don’t over- or under-fill jars.
  • Always make sure there is at least 1 inch of water covering your jars in the canner.
  • Do not skip the water bath for acidic foods. The water bath heats up the food in the jar, killing microorganisms. The heated food increases in volume—which is why you need to follow the rules for head space—and pushes out air. The water covering the jars makes sure no air reenters the jars. The air is heated, as well, making it expand and escape the jars. Less oxygen means less oxidation and less spoilage. (Except for anaerobic microorganisms like Clostridium botulinum, many microorganisms require oxygen.) You’re much more likely to get mold if you don’t conduct your water bath properly. Mold changes the pH of the product, making an acidic food more basic, which opens it up to C. botulinum, which in turn causes botulism.
  • Remove air bubbles after packing hot jars. Sometimes the food can contain enough air to alter the head space. That, plus extra air, means extra oxygen—and more chances for spoilage.
  • Always wipe the rim of your jars with a clean cloth before putting the lids on. This will help ensure a good seal and will remove yet another way for contamination to get inside the jars.

8. Take the rings off of your jars after they seal.

The rings are really just designed to keep the lid on while canning and should be removed after they seal. This will help reduce corrosion and rust on your jars—but, more importantly, removing the rings help you avoid a false seal. A failed seal indicates spoilage, but with the ring keeping the lid down, you wouldn’t necessarily know the food had spoiled. With some types of spoilage, smell, taste, and looks all can be deceiving. Once you’ve broken the seal, you can put the ring back on to avoid creating a mess.

9. Remember to adjust for altitude.

Determine your altitude then adjust your canning time. Please note that time differences may vary depending on the product you’re canning.

10. Use the right equipment.

Steam canners and oven canning are not recommended and cannot prevent the risk of all types of spoilage. A stock pot deep enough for your jars plus 1 inch of water is fine for water-bath canning. Make sure to fit a rack in the bottom of your pot, though. The rack helps keep water moving all the way around the jar and helps prevent the jars from breaking. Use a pressure canner, not a pressure cooker, when canning low-acid foods and meat. The gauges on most pressure cookers aren’t reliable, if they even have a gauge at all. Also make sure your pressure canner is in good condition. Old or poorly cared for pressure cookers are dangerous and can explode. Your county extension can test your pressure canner for you or direct you to someone who can.

By all means, canning isn’t something that should intimidate you. You just have to follow the rules to make sure your finished product is safe. (In fact, it’s similar to a trusted recipe: Following the proven guidelines actually makes things easier on you!) Properly canned foods are delicious and most times much healthier than what you can purchase at the store. So get out there and start canning!

HOMEGROWN Life blog: Rachel, of Dog Island FarmMy friends in college used to call me a Renaissance woman. I was always doing something crafty, creative, or utilitarian. I still am. Instead of arts and crafts, my focus these days has been farming as much of my urban quarter-acre as humanly possible. Along with my husband, I run Dog Island Farm, in the SF Bay Area. We raise chickens, goats, rabbits, dogs, cats, and a kid. We’re always keeping busy. If I’m not out in the yard, I’m in the kitchen making something from scratch. Homemade always tastes better!


3 Responses to “HOMEGROWN Life: How to Can Safely”

  1. Sarah Calabrese Says:

    Thanks Rachel. I found your piece very informative, and a little bit scarey. I now live in Florida and have a wonderful mango tree that I have made three years of mango chutney with and put lots of vinegar in for the acid but did vary on the recipe which I got from the internet. Sadly this year no mangoes but I am hoping the chutney from 2012 will last until next summer 2014. I didn’t know about taking the rings off and from now on will do that. Sarah

  2. […] careful research and reliable recipes if you wish to attempt canning and jam making on your own. Here is a great article by that offers tips for safe […]

  3. […] careful research and reliable recipes if you wish to attempt canning and jam making on your own. Here is a great article by that offers tips for safe […]

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