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How Pectin Works

Reader Eliza asks if I can say more about how pectin works. Reader Eliza, saying more is my specialty. So let’s get underway.

Pectins are long-chain sugars (carbohydrates, also known as starches) that are found in the walls of plant cells, particularly the walls of fruit cells, where they form a sort of elastic, moisture-retaining barrier that does double duty as a glue that holds the cells together. Occurring in tightly wound bunches, pectins are abundant in the skins of fruits (apples, grapes, berries, peaches, etc.) and are most numerous right before a piece of fruit reaches peak ripeness. Past that point, the pectin molecules being to degrade.

Pectins can be released by cutting up and/or mashing fruit, then heating it. As long as the surrounding environment is sufficiently watery, the pectin molecules will come loose, then disperse. Properly managed, those dispersed pectins will behave not unlike gelatin, which is an animal protein, and of course a handy thickener. However pectins are a little fussier to work with. As they spread out into a jam mixture they pick up negative electrical charges. That causes them to repel each other rather than bond to one another.

The jam maker fixes this problem by adding acid — usually in the form of lemon juice — which neutralizes the negative electrical charges and makes the pectin molecules want to play nice again. They come back together, only this time there’s quite a bit of flowing water between them. As they try to link back together, that water flow is restricted, and thickening is the result.

But there are risks involved in this delicate little molecular dance. Too much acid will damage the pectin molecules, making them un-linkable. Excessive or prolonged heat will flat-out destroy them, breaking up the flow-restricting network and causing a jam to thin out again. This is why, after a certain point, no amount of further cooking will cause a de-thickened jam to gel again. It’s also why, if you heat a mixture with packaged pectin for too long, the jam will still come out runny (though I never complain about a fresh fruit waffle syrup or ice cream topping).

These potential pitfalls make traditional jam-making a bit challenging for the beginner and the experienced cook alike. The process unfolds in four basic steps. First, the mashing of the fruit. Second, the gentle heating to release the pectins. Third, the adding of the acid to bring the pectin gel together. And lastly, the cranking of the heat to a roiling boil, which quickly concentrates the sugar syrup before too much of the pectin network is destroyed.

It all happens rather quickly and can be rather stressful. But the result is worth it: a jam that’s not just indulgently sweet and fruity, but that also glistens like crystal on the spoon. And if the result is a little runnier than a commercial jam, who cares? I’ll take that in a heartbeat over the overly-thickened mass-produced stuff. A jam with too much pectin not only has a duller taste than its looser pectin-light cousin, it has far less eye appeal, being cloudy with starch. Give me a spoonful of that flowing, sparkly fruit jewelry any day.

Is jam the only thing pectin is good for? No, but because it requires both acid and heat to activate — plus it needs to be administered in a fairly high concentration — it’s not as useful as many other commonly available thickeners. And that’s what I have to say about pectin. Thanks Eliza!

15 thoughts on “How Pectin Works”

  1. Enlightening, especially since I was just thinking about this, although in a roundabout way. You answered my question, which was this: what about when you cook fruit for pickling? I found a recipe for sweet & sour pickled peaches with habaneros; someone gave me quite a few of the hot peppers and I’m looking for ways to use them. Anyway, it got me to wondering why, when you pickle fruit, the liquid doesn’t turn into a gel. You’ve got the pectin from the skin, the sugar, etc. But of course, as you just mentioned, there’s a much greater amount of acid, usually in the form of vinegar. I didn’t even have to ask the question and you answered it. Amazing.

  2. It’s a different thing than pectin, of course, but I find Christine Ferber’s no-pectin approach for jam + a digital thermometer petty damned effective.

    She cooks the fruit with the sugar and lemon once and allows that to macerate overnight in the fridge. The first cooking is intended to let the melted sugar fully work its way into the flesh of the fruit. The following day she cooks it all again to 221˚ before canning.

    I find that that produces a really nice texture and brighter flavors. And no pectin drama.

    1. Very interesting indeed, Rainey! I’ll have to try that. Is her technique available online anywhere or just in a book?

      – JOe

      1. Her book is “Mes Confitures” (title is French but the text is in English). It’s great ’cause it has recipes for what’s available all year long. …including her scrumptious Banana Chocolate (or Chocolate Banana perhaps).

        I found this recipe online:

        Here’s one for her Banana with Bittersweet Chocolate that’s not out of season:

        Have fun experimenting! I’ve never been able to try one of her confiture but I really like her method. …which also doesn’t bother with a water bath.

        1. Looks like there’s a book I need to put on my birthday list!

          Many thanks, Rainey!

          – Joe

      2. Just want to second this method, which I’ve been using regularly to make strawberry and sour cherry jam for the past few years. It results in the most amazing, jewel-like appearance and clean flavors. It’s a 3 day process, but there’s very little hands on time. My sour cherry even won first place at a local farmer’s market contest last year 😉

    2. Pretty sure there is pectin in that recipe, pectin being an integral part of fruit. “No added pectin” maybe?

  3. I have had the odd bottle of preserved rhubarb become jellified over time. A bit off-putting, but fine when used in cooking.
    I have an excellent book on jams and preserves that was published by the Home Science Department at my university, it has this to say:

    The proportion of sugar in “preserves” is important and is determined by the amount of pectin in the fruit. (See page 7). Too little sugar – “preserve” will not set and/or will not keep.
    Too much sugar – “preserve” will not set, will be sticky or sugary and will be too sweet with a poor flavour.
    When a “preserve” is a half to two-thirds sugar by weight it will set. When a “preserve” is two-thirds or more sugar by weight it will keep. “Preserves” that are two-thirds (66%) sugar by weight will set well and keep well, i.e. 1 kg of “preserve” from 660 g sugar.
    “Preserves” containing less than two-thirds sugar have a good flavour and may set, but must be sealed hermetically, as for bottled fruit, for storage.

    And also:

    What Happens to the Sugar?
    Granulated sugar is a complex sugar known as sucrose. When sucrose is heated with an acid it is changed into two simple sugars. If too much sugar in a jam is changed, either by over-boiling the jam, or if there is too much acid, the preserve may not set and will be sticky, and simple sugars may crystallise out. If too little of the sucrose is changed, the preserve may go sugary on storage.
    The aim when making jams, etc. is to change about one-third of the sugar added. If 30-40% of sucrose has been changed the jam will keep perfectly and neither sucrose nor the simple sugars will crystallise out.

    And lots more along those lines.

    The book has several specific recipes, but its main value is that you can use the information contained in it to turn any overabundance of produce into a jam, pickle, or preserve.

    1. That jibes more or less with what I know about jam making, but I can always learn more! What’s the name of the book?

      – Joe

      1. It’s called “Jams, Jellies, and Preserves” but has been out of print for a long time, and was just a small soft-cover thing in the first place. I scanned my copy ages ago though, so can send you the pdf. Think I still have your email.

      2. Oops. “Jams Jellies, Pickles and Relishes”. Have emailed it to you. Take note that we do not usually “can” jams. We rely on the sugar content to preserve it.

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