Canning 101: Sugar’s Role in Home Preserved Food

July 25, 2012

The summer canning season entered its stride recently and ever since, I’ve been getting a ton of questions about sugar. I’ve written a lot of about sugar, but it’s mostly been buried in a variety of other posts. I figured it was time to devote an entire post to the stuff, since it is used so often in food preservation.

Sugar plays two roles in homemade preserves. First, it helps with set. Jam making has a lot in common with candy making, in that you are attempting to harness sugar’s ability to change texture at different temperatures. Jam is cooked to 220 degrees F, which is known at the gel stage. At this temperature, the heating sugar will bond with the pectin in the fruit and provide structure and spreadability.

This is particularly important when you’re working without additional pectin, but is also necessary even when you’re working with commercial pectin. If you’ve ever had a situation in which you’ve drastically reduced the amount of sugar in your recipe and then found yourself with a very runny product, this is why. You didn’t have enough sugar to elevate the temperature and so you weren’t able to cook to the set point.

Second, sugar acts as a preservative. High sugar products have a much longer shelf life than those with little to no additional sugar. This means that a low sugar fruit butter won’t last as long in your pantry as a jam made with a full complement of sugar. Fruit preserved in light syrup won’t hold as long as that preserved in a heavy syrup.

This also means that preserves made with alternative sweeteners and honey will also not last as long as those made with sugar. This is not to say that you shouldn’t sweeten with those alternatives, but it’s important to understand how it will impact your finished product before making those swaps.

To recap, sugar helps with set and it makes preserves last longer. That’s it. It does not make things safe. It is not a substitute for proper acidity. It does not inhibit the growth of botulism. If you want to reduce the amount of sugar, or replace it with an alternative, know the implications.

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55 thoughts on "Canning 101: Sugar’s Role in Home Preserved Food"

  • Good post, thanks. Can I ask a question that has been on my mind for a long time since I first discovered US based blogs etc about canning? I’m in the UK, and there is absolutely no advice (or indeed common practice) concerning the necessity of hot water bath canning jams, jellies, pickles or chutneys here. In fact, I have a shelf full of UK published (very good) preserving books, and not a single one advises canning any of these products. Pam Corbin’s River Cottage Preserves book does actually say ‘ A concentration of over 60 per cent sugar in a preserve creates an environment that is hostile to micro-organisms.’ Vinegar of over 5% acidity is also mentioned as being sufficient to create a hostile environment to the growth of micro-organisms. I wonder if the US version of this book contains different advice?

    I have never, ever, ever heard of a UK home cook, or UK preserving book, advising the hot water bath processing of jams or chutneys with traditional sugar/vinegar content. And these unprocessed jars are kept without refrigeration for upwards of a year. This is also the case for preserves that you can buy from small scale producers (a common practice here). I have also never heard of anyone getting botulism from their home made jam! Admittedly, there could well be cases that I don’t know about, but I would guess that if it had happened even occasionally, then the official advice around preserving would have changed over the years?

    So, what I wanted to ask was, do you have any ideas about this discrepancy between UK and US practice/advice? Are you guys being over cautious or are we taking our lives in our hands every time we crack open a jar?! Obviously I know that you won’t be able to waver from the official line in advice you give, but just wondered if you knew about this (and how much it has blagged my head as a US blog reading UK cook!)

    Love your blog and your recipes by the way (even if I do generally omit the final stage in the jams and chutneys…..!)

    1. I notice this, too. I tried to research and compare because I live in the US and my grandmother and mother never processed jams and jellies in a boiling water bath. They still don’t. I do, mostly because I am overly nervous. However, I still eat what they make. Reading in so many places that folks in Europe still consider eating jams that are not processed in the BWB made me more comfy about this decision, and I have never gotten sick. From what I have read it helps to reduce the likelihood of mold and get a very good seal on the jar.

    2. I’m English and although I follow the US guidelines when bottling (canning) food, I never ever water bath/can jams or pickles. Not even the WI do it!

      With regards to how common botulism is in the UK, NHS Direct says
      “Botulism is relatively rare in the UK. There have only been 33 recorded cases of food-borne botulism in England and Wales since 1989. Twenty-seven of these were linked to a single outbreak that was caused by contaminated hazelnut yoghurt. Since 1978, there have been eight cases of infant botulism. None of these cases resulted in death.”
      “Since an outbreak of food-borne botulism in 1989, where contaminated hazelnut yoghurt affected 27 people, there have been another six cases of food-born botulism in the UK up to 2006. All of these were caused by eating homemade food that was prepared in other countries.”

      Though I would never dissuade anybody from water bathing jam I am quite comfortable not doing it with (full sugar) jams and jellies and chutneys (which contain sugar and vinegar). I don’t feel I am risking anything, and I also don’t worry about lids sealing. Some do, great, but others don’t, but I store them exactly the same. When you think many British jam makers have used those cellophane tops instead of metal lids for years, I think any risk would have shown itself in the statistics by now.

    3. Hi, Beth. I’m new to the site, and hope to answer some of your questions. I see throughout the comment section there’s a bit of confusion not just regarding the role of sugar in canning, but the different contaminants among bacteria, molds, fungi, etc. There also seems to be a bit of extra confusion about botulism, which I’ll try to clear up. There’s so much to say about all of it; but that would take forever, so this will be as simple as possible.

      Sugar is primarily for taste in canning, but also has anti-spoilage properties. Never rely on it to keep food “safe”–that is, free from organisms which cause disease. It does make food take longer to spoil, but doesn’t eliminate them all together.

      I know others have said they don’t water-bath jellies and some other items. What you do to yourselves is your business, but please don’t allow your children/grandchildren or coworkers to eat it. The risk is low, especially with lower-concentrations of pathogens taken in by healthy adults. Elders, children, immune-compromised people (those on chemo, immunosuppressants, frank AIDS, etc.) could die. The commonest pathogens in improperly canned foods are Staph. aureus, Clostridium perfringens, C. botulinum, Campylobacter, Listeria, Bacillus cereus, E. coli, and Vibrio (parahaemolyticus). And that’s not including them all! Some of the molds can raise the pH of an acidic food above 4.6 pH, the safe level. As they eat (so to speak), they can destroy acidity, leaving room for the botulism spore to produce its toxin.

      Since water bath canning fruits and jellies takes under half an hour, start to finish (only five or ten in the canner itself), why would anyone skip this step? I don’t get it.

      With pathogens, you never eliminate them all. You’re trying to slow down growth or bring it to a standstill, so that the numbers of pathogens are lower than that required to cause illness. They need food, water, shelter, and something to breathe, just like any other life form. The human gut makes them very happy; drying them up, raising or lowering the temperature of their home, suffocating and starving them, makes them unhappy.

      Clostridium botulinum is a different kettle of fish altogether. There are seven strains, I think…I forget. They’re a bacteria, but they reproduce with spores, which means their “babies” are protected by a hard shell. This enables them to live quite happily in our air. That’s important, because they can’t breathe oxygen–they’re anaerobes, and can only reproduce outside its presence. Thus, while we’re suffocating all the other pathogens by canning them to produce that lovely seal, we’ve just made the environment perfect for C. botulinum to build a family, unless the pH is at or below 4.6.

      They aren’t in and of themselves particularly dangerous to healthy, adult humans, but the spores can cause what’s called infant botulism. At some point between the ages of three weeks to about eight months, babies’ guts can’t handle the spores, which overgrow and cause what’s called infant botulism. That’s why you should never feed a child under one year old honey–it’s a haven for C. botulinum spores. The word “natural” doesn’t mean safe; it only means natural.

      What makes the spores dangerous is the toxin they produce during reproduction. You can kill spores, but you can’t kill toxins, since they aren’t alive. The problem is that the organism doesn’t die at 212Β° F, which is as hot as we can get it in a water bath. It dies at 240Β° F, which can only be obtained under pressure. All vegetables and proteins are alkaline; that is, a pH above 7. Anything in the 4.6 range, such as tomatoes, can go either way. To be safe, the current standard requires that tomatoes be acidified.

      Now, C. botulinum can’t live in an acidic environment, so acidic foods don’t have to be pressure canned. Naturally acidic foods are most fruits, but we can acidify certain alkaline foods by adding acids to them, usually vinegar, lemon juice, or citric acid. Keep in mind that you can’t use home-made vinegars or balsamic vinegar, because they aren’t acidic enough. You need a strength of 5% vinegar to be safe, which all white distilled and commercial cider vinegars contain. Never use natural lemon juice, since as an agricultural product, its acidity can vary. Always use bottled. I know that sounds icky, but we’re not making a lemon meringue pie or salad dressing; we’re using it as a chemical to safely preserve food. You can also use ascorbic acid (Vitamin C), but it’s much weaker. Since the vitamin itself (not its acidity) is easily destroyed by heat, there doesn’t seem to be much point. There are stronger acids, much cheaper, and more easily available.

      I know this is terribly long, but I hope it helps. If something isn’t clear, please ask. FYI–I’ve been canning a long time, and been a Master Food Preserver since the early 1990’s. When I think about what I ate growing up, I’m shocked our whole family isn’t dead! lol I would never in a thousand years can the way my grandmother did.

      BTW, there aren’t too many deaths more unpleasant than dying of botulism. It’s excruciating. Recovery takes weeks, and sometimes months. Some people never fully recover their energy. Not a good thing. With modern medicine in the U.S., the mortality rate varies from 5% to 10%, but if a person doesn’t recognize early symptoms, s/he might not get to the ER soon enough. Elsewhere in the world, the death rate is far higher.

    4. I have canned some jams in jars that were sterilized first and have gotten a a good seal. I used them up in less than 3 months so I am not sure how long it would last. But I wonder if climate plays a factor. I live in the Deep South where temps get as high as 100F and we have very mild winters. Not usually lower than 50F for more than a couple of days in January or February. So I am not sure if that is a factor but I am willing to bet food would spoil much quicker in my climate.

  • Tried making jam with less sugar this year by using a pectin specifically for low sugar jam.. I dont know if we got ratios wrong or what but it was a nasty jelled mess! HA. I dont know that I will do that again.

  • This year I am seeking out only pure cane sugar to put up my peaches and blueberries. I have a feeling that some of my jelling issues may have stemmed from sugar being from beets and now all beet sugar is from GMO beets. Saying no to all GMO products this time and forever! I just did some research and found an article comparing beet and cane sugars in cooking/ baking. Anyway thanks for your great blog!

  • I’m sure you’ve written about this, but what about sugar in things like relish? I don’t really like a sweet relish, so have eliminated the sugar or drastically cut it down. Have I made a horrible mistake?

  • I just got your cookbook last night (Wow!) and discovered in your bio on the back cover. Great cookbook, great blog. I look forward to following your canning adventures! Thanks!

  • Beth,
    My mom often cans her high sugar or high acid foods by the “get it really hot and listen for the pop” method. Meaning no hot water bath, but very hot food and very hot jars. If any don’t seal they go in the fridge, but she’s never had any go bad that way. I like to hot water bath just because it ensures more of them will seal, personally.

  • I learned to can with my Mom years ago; we did not hot water bath our jams/pickles or really anything with a high sugar or vinegar content. When I bought a new Ball canning book a couple of years ago was the first time I heard of this step in canning those products. I’ve converted and use this step but really don’t like the texture of the pickles and the jam tastes overcooked so this year I’m leaving out that step, especially with high acid content foods like pickles. I’ve always hot water bathed my fruit and juices. This year I bought a pressure canner so I can process vegetables and meats/fish since I think the world’s food supply has many problems especially the GMO issue. I raise most of my produce and buy the rest from local sources that I trust.

  • I made low sugar jams the past two years, and have decided to experiment by using the low sugar pectin and topping out the required sugar. I really don’t like what happens to the jam as it sits on the shelf. The preserves quickly lost color, and they don’t last very long at all once they are opened. They are also my only ones to develop mold in the jar before opening (only one jar, though).

  • i actually have a question/suggestion for a canning 101 post. do you really have to peel tomatoes and peaches etc. when i’ve made peach sauce, apple sauce, basically any fruit sauce i never bother to peel them unless i’m either a) wary of my source and worried about pesticide residues or b) they have bad spots. i haven’t canned tomatoes yet, but it always calls for these to be peeled before canning as well, but i know my mother never bothered. I was just wondering if there was a food safety related reason why it is always part of the instructions for these things, in which case i would bother to peel them, or if it’s just the way its always been done.


  • I was up in Costco the other day with my canning friend Jenn and thought hard about buying a 25lb bag of sugar. Then I thought, where on earth would I put it if I had it. I definitely use that much in July and August though!

    1. I sent my husband to get the smaller of the two large size bags from BJs and he came home with the 25lb of sugar. I have not idea what I am going to do with that much sugar. I guess I better start making more jams or baking πŸ™‚

  • Considering the chemical death trap that sugar is (made with blood albumin and bone black from animals, milk of lime, and bleach) to “purify” it and then the addition of more chemicals and MSG, I think I will take my chances with it not lasting that long. Sugar has absolutely no nutritional value what so ever and sugar addiction was considered more of a problem at one point in the US that opium addiction.

    Pomona’s Universal Pectin uses 1/2 cup of honey to 4 cups of fruit and sets up beautifully if you follow the directions. I like to keep the taste and nutritional value of my fruit. πŸ™‚

    1. I would be curious to read about what you are saying sugar is made out of. What about organic sugar or pure cane sugar? Can you supply a link so I can read up on it? Thanks!

      1. Rapadura would be the only sugar that adds nothing and nothing is taken out. It is hand paddled over an open flame to evaporate the water.

        Sugar isn’t made out of those chemicals but “purified” by them. Even organic cane sugar is purified by these chemical methods. (My BIL’s father is a mechanical engineer for Crystal Sugar Company)

        Suicide by Sugar and Sugar Blues are excellent resources to learn more about sugar.
        William Dufty in his book Sugar Blues writes:

        β€œAfter all, heroin is nothing but a chemical. They take the juice of the poppy and they refine it into opium and then they refine it to morphine and finally to heroin. Sugar is nothing but a chemical. They take the juice of the cane or the beet and they refine it to molasses… and then they refine it to brown sugar and finally to strange white crystals.”

    2. Sugar was recently added to the list of addictive substances. I wonder what the food industry will do now. They replaced fat with sugar (for health reasons). I plan to try out some of the jams and include high pectin fruits to avoid chemical pectin.

      Sugar is on my list of food allergies. I wonder if it is due to the chemicals used to bring it to market. thank you for the honey to fruit ratio.

  • Many pickle recipes require quite a bit of sugar, so if you have cucumbers, that’s one way to use up all that sugar! I don’t buy in large amounts, but just buy as I need it.

    It’s interesting about the processing methods, as I think people did previously use really hot jams/jellies/pickles when canning and they did often seal. I prefer to water bath can (or pressure can) to insure a good seal on the product.

  • Thanks for clarifying things with sugar! I’ve always wondered about reducing or changing sweeteners in a recipe and now I know what I’m getting myself into.

  • Excellent post!

    What I like about your book is it is for “small batch” canning and I don’t need get a 25 lb of sugar! Especially since I’m not supposed to have refined sugsr and must use organic unrefined cane.

    By the way, LOVE LOVE LOVE the cantalope jam!!!

  • Thank you for this post. Just found this site via The Sassy Radish and it’s exactly what I needed. I tried making low sugar strawberry jam and it came out horrible πŸ™ Guess I’ll be on this site for a while.

  • If jams with less sugar (like the blueberry jam you recently posted) don’t last as long, about how long can I expect my jam to hold up?

  • Thanks, this was a really good summary about sugar. Most of the jams I make use natural pectin, with currants or apples, so I almost never reduce the amount of sugar, unless of course I want a runny berry waffle/pancake/ice cream topping instead of a traditional jam. Sometimes the mistakes taste even better than the intended product.

  • I am thoroughly convinced there is huge difference in the final product quality when using cane sugar vs. beet sugar. I think cane sugar is much better for canning, candy making and making cooked frostings, etc. I however have never been able to find any documentation for this. If your sugar does not say it is pure cane sugar, then you are probably using a sugar beet-derived sugar. If you are having less than stellar results with jams or candies, consider making sure you are using cane sugar.

  • I recently made a cucumber-infused simple syrup using a 2:1 ratio of sugar to water. Since there was so much sugar in it I wasn’t worried about it spoiling, especially since I’m keeping it in the fridge, but now I’m not so sure. Any thoughts?

  • Sugar is actually not the only preservative in jams an spreads. Dr. William Numer, the head of the UDAF (USDA) here in Utah has told me that repeatedly. Your acid content is. You are right that sugar, after boiling for periods of time, candies and makes your jam set “hard” because it is just that, candy. Not jam. In your store bought pectin, that is what your chemical reaction is. (and in some of your commercially purchase pectins too.. NOT Pomona and other brands, however.)

    I make jams with absolutely no sugar added all the time. If you use a traditional cooking method like they did in years past, when sugar was an item that most people could not afford and truly make small batch preserves by cooking the fruits for a long time, the starches in the fruit turn to sugar, and naturally sweeten the fruit. As you are a jam maker, you know what acids are (Citric -lemon and lime juice, vinegars and other natural, healthy products) so you do not have to add pounds of unhealthy sugar to your fresh fruit to achieve a good jam and set.

    I also do not like a stiff gelatinous glob in my jar of spreads of preserves. I like a nice easy spread that will not tear the bread apart. That comes from the cooking down of the fruit and achieving a soft natural spread.

    I agree that sugar is a newer method of canning, but not the good “old fashioned” way, like our ancestors did. Only the elite could afford it. And the elite did not can their own products. They bought them!! πŸ™‚

    1. Liz, I didn’t say it was the only preservative in jam, simply that it did offer a preservative effect. The goal of this post was simply to have a place to send people when they ask me whether they could safely reduce the amount of sugar in their jams. I needed to make it clear what sugar does and doesn’t do. This was not an endorsement of sugar, just an explanation of what it offers.

      Also, it sounds like you’re making fruit butter, not jam.

  • I don’t think you’re correct about sugar not reducing the risk of botulism. When sugar is at a high enough concentration, it binds to the water in the recipe, which makes less of it available to microorganisms (including the botulism bacteria.) That’s *why* high-sugar jams last longer than low-sugar jams; they have lower water activity. Botulism cannot survive in an environment with water activity lower than about .93. High-sugar jam has a water activity of around .85. Salt can also lower the water activity, but there has to be enough to make a difference.

    1. Beth, the thing is that most recipes don’t include enough sugar to reach that concentration to start out with. And any recipe that is designed for boiling water bath canning should also be high enough in acid to prevent the growth of botulism. So while what you say is true, it doesn’t apply in this conversation.

  • Can I safely sub brown sugar for white sugar in a canning recipe? I prefer brown sugar with pears. Thanks!

  • I have been searching the internet, and cannot find the answer to this question anywhere. I have recently converted from refined white sugar to coconut sugar as well as other sweeteners such as stevia and xylitol. I have read about the role of sugar in jam making. My question is: would coconut sugar act the same as refined white sugar in jam making? i.e. would it gel the same, and would the shelf life be similar? Or would the shelf life be reduced like it would for jams made with honey or stevia? Also, if I used coconut sugar, would I use the “no sugar needed” pectin, or the regular pectin? Thanks!

    1. Michelle, I honestly don’t know the answer. I’ve only used coconut sugar a couple of times, and each time I did, I was using it to sweeten a fruit butter where the set wasn’t dependent on the amount of sugar. It seems to have a similar preservative effect, though I only got my hands on some last summer, and so it’s just been a year. As far as what pectin to use, I don’t know that either.

  • A high concentration of sugar IS bacteriostatic against most all bacteria, including clostridium botulinum — the bacteria that causes botulism. The mode of action is simple, high concentrations of sugar OR honey pull the water out of bacteria making them unable to function. Honey also has additional components that are bacteriostatic.

    1. Please let me know by how much I can reduce the sugar and still produce a safe jam. Certo recipes require more sugar than fruit and simply do not taste like the fruit any more. I am not concerned with the set of my jam since I have recently learned that chia will do that function. I am only concerned with producing a safe product that has less sugar. My strawberry jam sets well and has no pectin but will it be safe in January?

  • I used Wal Mart sugar this year to make my jelly and jam well big problem it is not setting I did nothing different other than the brand of sugar any help would be appreciated. Thank you Sandy

  • Your explanation of sugar and pectin interaction is great but does not answer my question. I wanted to know how much sugar is needed to preserve jams. I am not concerned with the action of the pectin. I have begun to use chia seeds as the thickening agent but, I need to know how much sugar is needed to ensure that the jam will not become infested with some bacteria. I am not asking about preserving under boiling water where light syrup or even no sugar may be used. I do not wish to make dozens of jars of jam only to have them pop up the wrong way or spill over in my cupboards after only a few months. I sell much of my jams I need to know that they are safe.

    1. There is no one formula that can tell you exactly how much sugar will prevent the growth of bacteria, because the sugar levels in the fruit vary and the water content in the finished jam will also vary. If you are doing the boiling water bath canning process, you should be killing off the bacteria so there’s very little chance of the product going bad.

  • I’m starting my first pickling project with watermelon rind. My aunt sent me her recipe which calls for six quarts of cut up rind to six lbs (12 C, in her recipe) of sugar. I’d like to make the pickle less syrupy than hers, so can I reduce the amount of sugar safely, and can you estimate by how much? I’ve only got a scant two quarts of rind so I’m not making a ton, and I may skip the scary canning part and just give out jars to be refrigerated.

      1. Thank you for all of the information about sugar. I was making peach jam this weekend and noted the significant difference in the amount of sugar in your recipe for peach jam in Food in Jars (that is my go to recipe) and one in the Better Homes & Gardens publication that I borrowed from the library – 5 1/2 cups of fruit to 3 cups sugar vs. 4 cups of fruit to 7 cups of sugar.

  • Thanks, we were wondering about shelve life. And since my husband is a diabetic how would I calculate the amount of sugar in each jar? Would sugar evaporate with the juice that evaporates? Do I need a chemist.

  • I accidentally bought 25 pounds of super fine sugar. I need to convert 6 cups of granulated sugar. Everything I find says that it is slightly more and 1:1 substitute for small batches. At what point is it no longer a small batch? How do I convert it?

  • Hello, Marisa! I had a question regarding sugar in canning. Would it work to add, say, a couple teaspoons of sugar to a jar, drop in your peaches or whatever, and add not quite boiling water to the jar? I, of course, also add a teaspoon of lemon juice, but am trying to save time and money, as I often end up with more syrup than I need. Your thoughts?

    1. It’s a really interesting idea you suggest. I don’t see why not, given that it’s safe to pack peaches in just boiling water (they don’t hold their quality very long that way, but it is safe). If you try it, please come back and let me know how it works out!