Food preservation methods: Canning

We’ve had questions from new CSA members regarding home food preservation techniques and any relevant items that might make good holiday gifts. We’re thrilled that folks are thinking ahead to preserving next year’s bounty, as that’s the key to getting the most out of a CSA and building the economic sustainability of local foods in general. This series will present some of our experiences and advice, along with ideas for kitchen items that we’ve found to be useful investments as serious practitioners of home food preservation.

CANNING (Boiling water bath)
Canning heats and seals food in glass jars, using a large pot of boiling water, making it shelf-stable for a long period of time. It takes the most supplies, prep work and processing of any method, and must be planned for accordingly. It is also more dependent on having a critical mass of food to be preserved, as it is highly inefficient to heat a large water bath for just two jars of something, as opposed to the quick-and-easy packing of a few containers to be tossed in a freezer. However, canning allows the bulk preservation of many extremely useful staple foods that would require rows of freezers otherwise, and makes the preserved contents instantly usable when desired (unlike thawing or rehydrating).

Canning does raise more food safety concerns than other methods; the process must be done properly to ensure the food is safe to eat, and some items cannot be safely canned in a boiling water bath (pressure canners are more flexible, but are more expensive and not covered in this discussion). It is highly important to follow and understand reliable directions & guidance; this is available from numerous reputable sources and we will not be attempting to reinvent the wheel in covering this topic thoroughly. However, we are considering holding one or more canning demonstrations next year for CSA members interested in learning more.

Canning is generally most appropriate for high-acid foods (such as vinegar pickles) and/or high sugar foods (such as jam). Our canning effots this year included pickles (cucumbers, beets, & green tomatoes), relishes (zucchini & green tomato), crushed tomatoes, tomato juice, whole tomatillos, jams, fruit butters, applesauce, green tomato pie filling, and peach halves in syrup. Notice the green tomato theme? They were extra abundant this year. On the other hand, we didn’t get to some of our favorite canning recipes including ripe tomatoes, such as tomato paste and salsa, as there weren’t enough tomatoes to accomplish this.


Canning leaves little room for creativity in the kitchen; ingredient ratios often have to be just so to ensure a safe results. Recipes that are intended for canning should be followed precisely; recipes not labelled for canning should not be assumed to be safe for canning. For example, the Ball company (preeminant maker of canning supplies) has a large website devoted to guidance and recipes. Our primary reference for canning is the book So Easy To Preserve, available from the Georgia Extension; their website also seems to have most or all of the recipes & info from the book. That said, we occasionally tweak a recipe now and then, but only in minor ways that don’t mess with the ingredients or ratios that are critical to the food safety. For example, we once ran out of dill seed while making pickles, started substituting other spices in the same quantities, and discovered some really good spice combinations to make pickles more interesting (for example, a mix of cumin, coriander, fenugreek, cloves, and fennel makes amazing pickles).

The need to be careful to produce a safe product should not frighten people away from canning; it is no worse than handling raw meat in a proper manner or any other sensible handling of food products for which the home cook should be able to take responsibility.

Canning involves multiple steps, which we’ll only summarize because again there are many other thorough references available (such as this complete timeline) Empty jars are heated in a large boiling water bath, then packed with hot food (either complete liquids like applesauce, relish, and jam; or solids like cucumbers and tomatillos surrounded by a pickling liquid). Metal lids with rubber seals are applied, held in place by a screw-on ring. The jars are returned to boiling water for a recipe-specified time to ensure food safety, then removed to cool. The process of cooling creates a vaccuum within the jar, compressing the lid to create an airtight seal which allows the food to be stored at room temperature for a year or more.

This all takes time, including bringing a large quantity of water to boil, preparing all the food ahead of time, processing the jars, and so on. With experience you’ll learn how long each of these take, and learn to balance the tasks to take a minimum of time. For example, with pickles I’ll often start the water-bath pot going before I even start to cut up cucumbers, whereas prepping and cooking down applesauce takes far longer before you’re ready to can. In some cases you might break the work into two days, such as making applesauce one night and reheating it the next night along with the water bath to do the actual canning.

Jars may be reused, though with each use their chance of breakage increases with varying levels of loss. Cucumbers may be salvaged from a pickle jar which breaks in the water bath and eaten fresh; applesauce which took half an evening to prepare and cook will disperse through the water and be a total loss. We generally use new jars for high-value items like applesauce and tomatoes, reserving used jars for lower-value or salvagable items like pickles and tomatillos. Lids should NOT EVER be reused, as the rubber seals cannot be guaranteed through more than one use; the metal rings are fine as long as they’re clean and unbent.

  • Canner & jar holder: These large black pots come in two sizes, one that can hold pint-size and smaller jars, and one that can hold quart jars. (We have one of each.) The rack that comes inside the canner keeps jars from bouncing around next to each other.
  • Jar lifter: a special and necessary tool that safely lifts hot jars into and out of boiling water.
  • Metal funnel: Needed for getting food into the jars with minimal mess. We prefer metal to plastic given the amount of hot-boiling material involved.
  • Thermometer: This is helpful for maintaining the temperature of the water that the lids sit in before being put on the jars. The water should be around 180ºF. Boiling the lids before they go on the jar can ruin the seal.
  • Bubble remover: Bubbles will sometimes form in the food as it goes into the jar, and these should be worked out of the food before putting the lid on. We’ve found that a small wooden spoon works reasonably well. A small, heat-resistant rubber spatula might be an even better choice. Some canning starter kits come with plastic bubble removers, but we prefer to avoid plastic. We’ve read not to use metal utensils to remove bubbles becaues they can scratch and weaken the jar. 
  • Kitchen scale: not always necessary but helpful for judging product quantities.
  • Jars, lids, and rings
  • Large soup pot for preparing sauces or brines

All needed supplies are widely available at grocery and hardware stores, at least in our area. I estimate a starting setup would cost $50-$60, all of which will last a long time. Jars which cost about $1/each for quarts (including rings & lids), and should give several years of use with careful handling.

One thought on “Food preservation methods: Canning

  1. Eric this is really helpful, thank you. I've been interested in canning but also a bit intimidated of trying it, and the start up costs and legwork make it easy to just say, "oh, next year." It seems like canning though is one of those skills that are easily worth the time and effort it takes to learn. What I really want to do is pickles (for snacking) and tomatoes (for sauce through the winter/spring). Anyway, I'm going to remember this post as a reference when I give it a try.Also, you are an incredibly prolific blogger, putting this professor to shame with your writing productivity! You may have a career in academia 🙂