Jam is one of the most traditional things you may can at home - and it's often the first thing beginning canners attempt. But it's not necessarily easy to create a successful jam. This isn't because jam-making is difficult per se - but there are certain rules to follow and steps to take that many people simply don't know about. So let's fix that! Read on to learn everything you need to know to produce successful jars of jam. 

Jam vs. Jelly vs. Preserves vs. Conserves vs. Marmalades

First, let's get some basic definitions out of the way. "Jam" is made by cooking sugar and crushed or chopped fruit together. "Jelly," on the other hand, is made by cooking sugar and fruit juice; the end result is gelled syrup. 

"Preserves" are a mixture of jam and jelly: they contain small, uniform pieces of fruit (not the mashed fruit seen in jam) that float in gelled syrup. "Conserves" are similar to jam, but include not just fruit, but nuts, raisins, or coconut. "Marmalades" have little pieces of fruit - usually citrus - floating in gelled syrup. 

Once you know how to make jam, however, all the other variations (jelly, preserves, conserves, and marmalades) are easy to make following the same principles. For the purposes of this article, I will refer to all these variations simply as "jam."

Home canned blackberry jam.

The Four Pillars of Jam

There are four vital things every jar of jam requires: 

1. Fruit

2. Pectin

3. Sugar (usually; more on that in a moment)

4. Acidity

Fruit is the base of almost all jams, but not all fruits are suitable for jam-making.

For example, it's a myth that low-quality fruit (such as fruit that's fallen off the tree) is perfect for jam-making. In fact, bruised fruit encourages the growth of microorganisms in the jar, and overripe fruit lowers the acidity of the jam. Both these things may result in a poor quality end product - or even in a product that's unsafe to eat after it's sat in the pantry. As with all canning, jam-making doesn't improve the ingredients you start out with; for the best quality jam, use high-quality fruit. 

If you are planning to make the jam shelf stable (as opposed to making refrigerator or freezer jam), you'll also want to make sure the fruit you are using is safe for home canning. An example of a fruit not to use, for instance, is white peaches, which are too low acid. If you cannot find a modern (2016 or newer), tested safe recipe from Ball, Bernardin, or The National Center for Home Food Preservation, then it's likely the fruit is too low acid to be safe for home canning.

Freezing strawberries for jam-making.

Without pectin, no jam will gel. Natural pectin is found in many fruits, but especially in tart or under-ripe apples and crabapples, unripe blackberries, lemons, limes, currants, gooseberries, plums (not Italian varieties), Eastern Concord grapes or sour grapes, and quince. These fruits do not require added pectin in order to make jam; in fact, if you're making a jam from lower pectin fruit, you may add one or more higher pectin fruit to get a good gel without using store-bought pectin. 

Store-bought pectin is made from either citrus peels or apple pomace and comes in both powdered and liquid form. (These two forms are not interchangeable in recipes.) Store-bought pectin is only necessary when making jam from lower pectin fruit. It's also possible to make your own homemade pectin from tart apples. 

Pectin by itself won't create the desired gel for jam, however; in most cases, sugar is also required. Sugar attracts water molecules, allowing the chains of pectin to move closer together, which is what creates a gel. Cane or beet sugar does the best job of this, but it's also possible to use other sugars, like honey or fruit juice. Pomona's Pectin is an exception to the sugar+pectin = gel rule. In fact, this brand of pectin doesn't require any sugar at all; instead, it uses calcium (included in the package) to create a gel. 

In jam-making, sugar also inhibits the growth of bacteria once the jar is opened - meaning a higher sugar jam will last longer in the refrigerator than a jam that is low in sugar. 

Making low-sugar jam with Pomona's Universal Pectin.

Acidity is vital in any type of canning. Probably most canners know, for example, that high acid foods (fruits, pickles) are safe for water bath canning, but low acid foods (meats, non-pickled vegetables) must be pressure canned in order to effectively kill off dangerous microorganisms particular to those low-acid foods. However, acidity plays another role in jam-making: If there is too little or too much acid in the recipe, the jam won't gel properly; it will either be runny or too stiff. This is why some jam recipes call for the addition of lemon juice. 

Can I Make My Own Jam Recipe?

Because of the needed balance between fruit, pectin, acid, and sugar, canning your own jam recipes is not recommended. As a representative for The National Center for Home Food Preservation told me, "Without having laboratory equipment available for testing, it would be impossible to calculate if you have the recipe proportions correct. Therefore, we have to recommend not canning home recipes." 

However, it is possible to whip up your own recipes and then freeze the resulting jam. The instructional insert in the Pomona's Pectin box offers a basic recipe to follow for your own freezer jam recipes, or you may follow this formula for freezer jam: 

3 lbs. fruit, cut into 1-inch chunks, if the fruit is large 

3 1/2 cups granulated sugar 

2 tablespoons lemon juice 

1 box powdered pectin (if the fruit is not naturally high in pectin) 

Can I Reduce the Sugar? 

Traditional jam recipes contain as much (or more!) sugar as they do fruit, but there are ways to successfully reduce the amount of sugar in jam. One is to use fruit juice, along with a "low sugar" commercial pectin. (The box will include appropriate low sugar recipes inside.) However, it's important to bear in mind that fruit juice is just another form of sugar. 

A better method is to either use sugar to taste in a freezer jam recipe or to use Pomona's Pectin, which requires no sugar (though adding sugar for flavor is perfectly safe).

The only alternative sweeteners that are tested safe for canning are Stevia and Splenda. Other man-made or alternative sugar substitutes (including monk fruit, erythritol, and allulose) shouldn't be used for canning because they can change the pH and desnity of the jam, potentially making it unsafe to eat. 

Canning fig jam.

Can I Make Other Changes? 

Just because you need a tested safe recipe to can jam doesn't mean there aren't safe ways to alter those recipes to make them your own. For example, it's safe to add orange or lemon zest to jams. (Use up to 2 teaspoons in a recipe that makes 8 or more half-pints of jam.) I recommend adding it after the jam has reached its gel point. 

It's also safe to add 2 to 3 teaspoons of ground spices to a recipe that makes 8 or more half-pints of jam; if you add them before or during the cooking process, they will tend to develop a bitter flavor. You may place the spices in a spice bag that is removed just before canning or stir the spices directly into the jam. 

Can I Change the Jar Size? 

Tested safe recipes for canning jam will specify jar size, which is usually 8 oz. or less, although The National Center for Home Food Preservation does have a few safe jam recipes for pint jars. 

Never can jam in a larger jar than what the recipe calls for because you have no way of knowing how long to process it in order to kill off harmful microorganisms. You may safely use a smaller jar size than what is called for, but you must retain the processing time in the recipe. 

If you are making freezer jam, you may use any jar size you desire, but remember that once the jar is opened and in the refrigerator, it's vulnerable to molding. Therefore, a smaller size jar that you will eat through quickly is a better choice than a larger jar that will take longer to eat through. Also, for freezer jam, avoid jars with "shoulders" and instead use glass jars that are straight up and down the sides. (Jars with shoulders are much more likely to break in the freezer.)

Jarring freezer jam.

Do I Have to Process Jam? 

Years ago (and in some parts of the world still), jam was never processed in a canner. People simply put hot-off-the-stove jam into piping hot jars. They then either sealed the jars with wax or placed a two-piece canning lid on the jar, then flipped it upside down. Both of these techniques create an environment that is ideal for the growth of microorganisms...and our ancestors knew that - at least in a vague way - because jam often developed mold using these old-school methods. Their solution was to simply scrape off the mold and eat the rest.

What our ancestors didn't know, however, is that improperly canned jam can harbor E. coli, salmonella, and listeria, and once mold appears on jam, it changes the pH of the product, opening it up to the formation of botulism toxin. We also know that certain molds produce mycotoxins - some of which are cancer-causing. Scraping the mold off the top of the jam is insufficient, as mycrotoxins can be present throughout the entire jar, even if they are not visible to the naked eye.

The good news is, water bath canning jam is actually faster than using the old wax seal method. Also, if you plan to put the jam directly into the freezer, or if you only make enough jam to sit in the fridge for a few weeks, there's no need to process the jars in a canner. 

The Biggest Jam-Making Mistake 

Probably the biggest jam-making mistake I see people make is not testing the jam for a good gel before it goes into a jar. Some people throw the fruit, sugar, and pectin together, cook the ingredients for a set amount of time, then jar it and call it good. But by doing this, you may end up with syrup, rather than jam. 

There are several ways to test for a gel, but the easiest it to use a thermometer. Jam gels at 220 degrees F. sea level. (If you are at 1,000 ft. above sea level, the jam must reach 218 degrees F. 2,000 ft = 216 degrees F. 3,000 ft. = 214 degrees F. 4,000 ft. = 212 degrees F. 5,000 ft. = 211 degrees F. 6,000 ft. = 209 degrees F. 7,000 ft. = 207 degrees F. 8,000 ft. = 205 degrees F.)  

However, this only works if your thermometer is accurate! I can't tell you how many jars of jam I ruined by using an inferior thermometer. Finally, I broke down and bought a Thermapen, which I highly recommend - but any calibrated thermometer should do the trick. 

However, if you don't want to buy a good thermometer, other options are available. My second favorite method of testing for gel is this: Place a few saucers in the freezer before you begin jam-making. When you think the jam is done (and I recommend testing early and often), take a teaspoonful and place it on one of the saucers. Wait a couple of seconds, then run your finger through the jam. If a clear path is left where your finger went through, it is properly gelled. If the jam runs back into the trail your finger left, it needs to keep cooking. 

Testing the gel.

Another time-honored test is to use the sheeting method (sometimes called the spoon method). I admit I have trouble with this one, but some people swear by it: Place a cold metal spoon in the boiling jam and then lift it up and allow the jam to fall out of it. When the jam just begins to boil, the mixture will form drops that fall off the spoon. As the mixture boils, the drops become heavier and will come off the spoon two at a time. Once two drops cling together to "sheet" off the spoon, the jam is gelled. You can see illustrations of what sheeting looks like over at The National Center for Home Food Preservation website.

Do remember that jam thickens as it cools and that it can take up to two weeks for jam to fully set. 

Other Jam-Making Tips 

* Don't increase jam recipes; doing so tends to result in jam that doesn't gel properly. 

* Use a low, wide pan, since this will allow the jam to cook more quickly. It also allows water to evaporate from the jam readily. Using a pan with a thick base helps prevent burning. 

* Using fresh fruit at room temperature helps sugar dissolve more readily. 

* It's fine to use frozen fruit for jam making, but always thoroughly thaw it first. When canning jam from previously frozen fruit, you must use include the juices that thaw off the fruit in your measuring and cooking, for safety reasons. 

* Leave 1/2 inch headspace in the jar when freezing jam. For canning, use 1/4 inch headspace. (Headspace is the amount of space between the top of the food in the jar and the top rim of the jar.)

* Up-to-date, tested safe recipes always call for a water bath processing time of 10 minutes, - although there are still a few recipes that call for sterilizing the jars in boiling water for 10 minutes, then processing the jam for only 5 minutes. (It is safe to skip the sterilization of jars as long as you increase the processing time to 10 minutes.)

* When jam is processed for at least 10 minutes, there's no need to sterilize canning jars before canning. Do sterilize jars before bottling freezer or refrigerator jam, as this will help them last longer.

* If foam rises to the surface when cooking jam, skim it off with a ladle. Or at the end of cooking, stir in the same direction until the foam is greatly reduced. (Foam is just trapped air.) 

* Adding butter to jam in order to dissolve foam is controversial. While some pectin manufacturers recommend it, the Extension Offices note that it can create off flavors if the jam is stored for any length of time. 

* Always follow the directions in your modern, tested safe recipe. The order ingredients are added will vary according to the type of pectin used - and it's important to follow that order. 

Cooking jam.

Troubleshooting 

Crystals form in the jam: This is usually caused by using too much sugar or by not fully dissolving the sugar when cooking the jam. Cooling the jam too slowly can also result in the formation of crystals, so always remove the jam from the hot burner as soon as it has come to the gel stage. When making grape jelly, prevent crystals by refrigerating the juice overnight, then straining it before proceeding. 

Jam is too soft: Insufficient acid, incorrect proportion of sugar and fruit, overcooked fruit or fruit juice, or overcooking the jam in general may cause the end product to be soft. 

Jam is too hard: Overcooking the jam, adding too much pectin or too little sugar, or having the wrong amount of acid in the recipe can cause jam to be hard or tough. 

Jam has bubbles: If bubbles are on the surface of the jam, scrape or stir off the "foam" created during cooking. Bubbles throughout the jam may indicate spoilage. 

Jam is weeping: Using too much acid or storing the jam in an area that is too warm or has a fluctuating temperature can cause weeping. 

Jam is cloudy: Using under-ripe fruit, letting the jam sit before ladling it into jars, or, for jelly, imperfect straining (usually squeezing the jelly bag), can cause cloudiness. 

Jam has separated: It's normal for fruit to float in jars of jam and this is not a safety issue; it happens because there is air left in the fruit. This issue is easily overcome by simply stirring the jar when you open the jam. However, if you wish to try to prevent separation, chop the fruit into smaller pieces before cooking it or mash it with a potato masher while cooking. 

How to Save Runny Jam  

If you follow the advice in this post, runny jam should be a thing of the past (unless you're experimenting with your own recipes for freezer jam). But if you happen to make a runny batch, you don't have to use it as syrup. You can reprocess it. (Remember that jam can take up to two weeks to set.) 

1. Measure out no more than 8 cups of jam that needs reprocessing. (If you have more than that, work in batches.) 

2. For every 4 cups of jam that you're reprocessing, whisk together 1/4 cup sugar and 1 tablespoon of powdered pectin. 

3. Pour the jam into a pan (remembering that a low, wide pan is best) and add the sugar/pectin mixture. Stir until the sugar is completely dissolved. 

4. Prepare clean canning jars, your water bath canner, and new lids. 

5. Bring the jam to a boil and boil vigorously for 5 to 10 minutes, stirring constantly. Test for gel. When jam is done, remove the pot from the hot burner. 

6. Pour the jam into the prepared jars. Bubble, wipe the rims, and place new lids on the jars. Process in a water bath canner for the required amount of time, according to the recipe. 

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A version of this post first appeared in Self-Reliance magazine, issue #30.