How To Make Fruit Jam

Cooking Lessons from The Kitchn

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In the summer when the berries and stone fruit are in abundance, I make a fresh, single jar of jam at least once a week, sometimes even more. The entire process, from cutting the fruit to spooning the cooked jam into a jar, takes about 15 to 20 minutes. I don't can it in a water bath; I just stash it in the refrigerator. 

It's so much simpler than large-batch canning projects that it's unfair to compare the two, but the end result is just as delicious, if not more so.  All week long, I dip into a jar of fresh, brightly colored jam, spooning it into yogurt or on top of ice cream, or swirling it into a cocktail.  And, of course, spreading it onto my morning toast!

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Despite the fact that there are many good reasons to use commercial pectin to help jam set and get thick, I prefer to make my small-batch jam without it.  It's one less ingredient to track but also, I've just never needed to use it. A smaller batch of jam requires less cooking time (usually less than 10 minutes), so the flavor and brightness of the fruit really comes through. These quick jams also have a nice sticky, jammy texture without added pectin, so I've felt no reason to go there. To achieve this, however, there are a few things to keep in mind.

The Fruit

Many summer fruits make great jam.  The most popular are apricots, strawberries (and all manner of other berries such as blueberry, raspberry, and blackberry — check out Megan's recipe for Triple Berry Quick Jam), peaches, nectarines, grapes, and figs. The fruit will vary widely in sweetness so be sure to taste your fruit before cooking. If it tastes tart, you may want to start out with more sugar than this recipe calls for, maybe closer to 1/3 cup.

Generally speaking, slightly underripe fruit contains more natural pectin than ripe fruit and ripe fruit is naturally higher in sugar and more developed in flavor. This means that, ideally, you want to have a mix of some underripe and some ripe fruit for your jam. But single-batch refrigerator jam is often about using up excess fruit that would go bad if you hung onto it for much longer or about taking advantage of a super sale at the market and coming home with more than you can eat. It's about keeping it simple and using what you have. So there are a few cheats you can use to hedge your bets, such as the addition of lemon or kiwi (see below).

I've read in many places that mashing the fruit in the sugar helps to release pectin, so I also do that.  I do not know the science behind this but it seems to work, so I haven't questioned it.  Do you know if this a fact or another cooking myth?  Let us know in the comments!

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The Lemon

Lemon is used in jam to add acidic balance and pectin. I try to have a thick slice of lemon on hand when making my jam, which usually isn't much of a burden as lemon is a staple in my kitchen. After squeezing the lemon slice into the fruit and sugar, I then toss it into pot to cook along side the jam. There's a lot of pectin in the rind, so this is a little nudge to help things along. (Hint: Using a piece cut from the tip of the lemon gives you more rind.) 

Fish out the lemon when it's time to transfer the jam to a jar and discard it. As mentioned, lemon is frequently used to help balance the jam's sweet/acid ratio, so do try to use it regardless of your pectin ambitions. Also, since you will be boiling it in your jam, try to use an unwaxed, organic lemon or be sure you wash your lemon really well.

If you don't have any lemon on hand, you can add a small wedge of kiwi (about 1/4 of a fruit, peeled), which you can just mash in with the fruit (it won't add much flavor). A long piece of peel from a green apple (5 inches or so) will also help, but it should be removed, like the lemon, before transfering the jam to a jar.  

The Sugar

It's hard to give an exact quantity of sugar since fruits vary in sweetness, even from piece to piece and from day to day within the same kind of fruit.  So I start with a small amount, a ratio of 1/4 cup sugar to 2 1/2 cups of fruit, and then add the lemon. After the fruit has boiled for 5 minutes, I taste a small, cooled spoonful and add a little more sugar if needed. Often it doesn't. The strawberry jam pictured here ended up with a total of 6 tablespoons of sugar, or 1/4 cup plus 2 tablespoons.

The Salt and the Foam

I always add a small pinch of salt to my jam.  I find it balances the sweet and tart and seems to brings everything together, but it is optional. Also, I never skim the foam from the top of my jam. This is a habit born of laziness, but since I've never noticed a difference in the final product, it has become my method. I find that a little foam rises about midway through cooking the jam, but then it eventually cooks away. If the foam appears particularly scummy (grayish is color) I might do a quick skim, but the truth is that rarely happens.

The Frozen Spoons

My first step in making this jam is to put two or three metal spoons in the freezer. You will need these to check the consistency of your jam. 

After your jam has boiled for about 5 to 8 minutes, it's time to check to see how it's setting up. Simply dribble some hot jam from the pot onto the frozen spoon and wait a few seconds for it to cool. 

Run your finger through the jam — if it makes a clear path through the jam and doesn't fill in, then you have a good set.

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More About the Set

Jam made without pectin is generally a little runnier than jam made with pectin but it is still jam — that is, it gels into a sticky, cohesive mass when cool.  When it's hot, it will be a lot runnier so it's sometimes hard to tell if it has set enough. 

There are a few tricks, such as the frozen spoons previously mentioned (some people freeze small saucers instead and dribble the jam on the cold saucer to see if it sets).  Another trick is to check for sheeting. This is when you hold the spoon up and observe the liquid jam dripping from the spoon back into the pot. The drops will start off dripping as thin, individual drops but if the jam has set, the will soon to form together into a bigger, slightly thicker drop (or sheet) as it falls from the spoon. This post from Marisa McClellan has some very helpful information on setting, too.

I've also noticed that paying attention to the bubbles is a clue. When the jam first starts to cook, the bubbles are larger and thin. As the water starts to evaporate and the jam starts to thicken, the bubbles become smaller and tighter. Also, you can't 'stir it down.' That is, when you stir the jam, it still stays in a full boil. When this happens, it's good to bring out the frozen spoon and start checking.  

The Jar

I use any half-pint jar with a lid that I happen to have on hand to store my jam. Pretty ones are nice and add to the overall experience of using the jam but any will do. I wash the jar just before I use it but I don't sterilize it since I'm not trying to make it shelf-ready. I also re-use the same lids as long as they haven't rusted and still form a good seal. The amount of fruit described in this method usually makes enough jam to fill one half-pint jar, and it's easy to spoon it in without a funnel if you choose a wide-mouth jar. Less to clean up! I also label the jar with the fruit and date, even though it's destined for a short-lived life in my fridge.  

How To Make Basic Fruit Jam

Makes about 1 half-pint jar

What You Need

Ingredients
Fruit of your choice, enough to make 2 1/2 cups once diced (See Recipe Note)
1 lemon
1/4 cup of sugar, plus more as needed
A pinch of salt

Equipment
2 or 3 metal teaspoons
Knife and cutting board
Measuring cups
2- to 3-quart, heavy-bottomed pot
Potato masher or large fork
Spatula or wooden spoon
Clean half-pint jar with lid

Instructions

  1. Freeze the spoons and prep the fruit: Put the spoons in the freezer. Cut your fruit into large chunks, discarding any pits, cores, or heavily bruised sections.  Slice a 1-inch wedge from the end of the lemon.

  2. Combine the fruit and sugar in the pot: Combine the fruit and the sugar in the pot along with the pinch of salt. Squeeze in the lemon and then drop the rind into the pot. Turn the heat on to medium and mash the fruit a little until a chunky texture is reached. Don't mash the lemon too much as you will want to fish it out later.

  3. Cook the fruit: Bring the mixture up to a boil, stirring frequently. When a boil is reached, keep an eye on it, still stirring frequently.  

  4. Check for the set: When the bubbles become smaller and thicker, after about 5 to 8 minutes of boiling, start checking to see if the jam has set. Remove a spoon from the freezer and dribble several drops onto the spoon. Wait a few seconds, and then run your finger through the jam. If it leaves a distinct track in the jam, it is done. If not, keep cooking the jam and test again a few minutes later.

  5. Check for sweetness: When you test for the set, also taste the cooled jam in the spoon. Add one or two tablespoons more sugar as needed for sweetness or a touch more lemon juice for acidity. Stir it into the jam and continue to cook until the set is reached. (If the jam is set when you tasted it but you want it a little sweeter, add the sugar and cook for a minute or two to dissolve.)

  6. Jar it up! Turn off the heat and carefully spoon the jam into the jar. Set it aside to cool, then screw on the lid, label it with the fruit and the date, and store it in the refrigerator, up to three weeks. Enjoy!

Notes:

  • You can also freeze this jam. Just be sure you have left 1/2-inch of headspace in the jar or container so the jam can expand while freezing.
  • It's difficult to give an exact number for the pieces of fruit needed per batch, as each fruit is different size and weight. But as an example, I used one full pint basket of fruit for the strawberry jam pictured here.  
  • Fruit varies in water content as well, and some fruits may take longer to jam up. Just pay attention to the bubble size, sheeting, and use the spoon test!

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(Images: Dana Velden)