How to Make Jam (Jam 101)

many jars of jam

I am often asked how to make jam, and is making jam hard? People tend to assume it takes a lot of time; that every batch is unmanageably huge; that it’s scary and uses weird equipment. All this is so, so wrong. You can make jam in a skillet or saucepan in less than an hour. If you can boil water, you can make – and can – jam.

Let me explain here in detail. It’s not really hard, and it’s only a 3-step process:

  1. prepare the fruit, the jars and the lids
  2. cook the fruit into jam
  3. fill and seal the jars

Once you know how to do these things, you’ll be ready to make any kind of jam. If you want a big batch with a big result, you’ll want big pots. If you’ll be happy with a few jars, start with just a bit of fruit, and use smaller pots. I’ll explain the whole process, and provide notes for small batches as we go along, so if you have a small kitchen or only a quart of berries, stay with me!

This is not a recipe. This is a post about the process of making (and canning) jam. Check my “Jams and Jelly” category index to find a specific recipe you’d like to make.

A note on quantity

Make jam in small to medium batches. I never make a batch with more than 4 quarts of prepared fruit, because the quicker jam cooks, the fresher it tastes, and a large batch takes much, much longer. I’ve made jam with only 2 cups of fruit: though that, admittedly, made just one small jar for the next day’s special brunch.

STEP ONE part 1: prep the fruit

Handle the fruit as gently as possible. Fill a sink or basin with cool water, add in the fruit, a quart or so at a time. Swish it around a bit, to dislodge any sand or grit. Pull from the water and put on towel-lined cookie sheets in a single layer.

Remove any green stems and leaves. Cut or slice the fruit (I like to slice strawberries horizontally) into a large 4-cup measuring cup. Pack the fruit down a little bit.

How much sugar?

All jams need sugar, that’s what makes them jam. The trick is to figure out how much sugar to use. There isn’t a set ratio (you want between 40% and 70% sugar, by weight, compared to the weight of the fruit) because not all fruits are equally sweet. If I have a low-acid (and low pectin) fruit like strawberries, I’ll use close to the 70% level. For every 4 cups of fruit, my general rule of thumb is to use 3 cups of sugar. NOTE: 2 quarts of strawberries will yield about 6 cups of packed berries, so using that 4:3 ratio, use 4 and one-half cups of sugar. Or slice more strawberries until you have 8 cups of packed berries. 

On the other hand, many fruits are much less sweet. For blueberries, which are high in pectin and acidity, I’ll start with about 40% sugar. Apricots or plums, about 45%; dark (sweet) cherries and peaches, about 60%. Any of my recipes will disclose just how much sugar I actually use.

What about acid?

Most fruit contains some acid, but I always add lemon juice or another acid to a jam mixture. I want to be sure the acidity is high enough, and because I like the flavor a bit of acid brings. There’s no rule of thumb for how much acid to add to a jam, but you can get it right by adding it bit by bit and tasting along the way.

I generally add one ounce of lemon juice for every two pounds of fruit when working with higher-acid fruit (like tart plums), and about two ounces for lower-acid fruit (like strawberries).

What kind of pot?

You will need a larger pot than you might think you would – when making jam, the volume of fruit and sugar will expand at least double, and as much as triple! Plan ahead, use a big pot. Wider is better than taller, because you want to encourage evaporation. For this example using 2 quarts of fruit, a 4-quart pot is big enough. I have a favorite pot that I love. For bigger batches, I use a large 10-quart Maslin pan.  

What does macerating mean?

Maceration is really simple: layer the fruit and sugar in a pot or kettle. Fill the pot slightly less than halfway, to allow for the increase in volume when it boils. When all is in place, stir until thoroughly mixed, and then let stand, covered, in a cool place (or in the refrigerator) a minimum of 2 hours and up to 12 hours, so that the sugar will draw juice out from the fruit. NOTE: I like to crush strawberries or blitz with an immersion blender when I make jam; other folks like to see intact slices or even tiny whole berries. The bigger the pieces you like in your jam, the more gently you need to stir. 

STEP ONE part 2: prep jars and lids

empty jelly jarsYou will want the jars and lids to be ready when you begin to cook the jam. You will need sparkling clean jars and lids. If you have a dishwasher, you could put the jars through a dishwasher cycle, to have them hot and ready to use. Why do you want hot jars? Because you’ll be putting hot liquid jam mixture into the jars, and you don’t want them to crack from thermal shock.

If you’re making a small batch that will yield 5 jars or fewer,  and you’ll be sealing jars in a waterbath process, it’s easiest just to boil the jars. Put clean jars in a big pot of water that will cover them completely, bring the water to a boil, and boil 10 minutes. Turn off the heat, and hold the jars in the hot water until use.

Wash the flat lids in warm soapy water, and set them aside on a clean towel. NOTE: yes, just wash them. Lids have changed! Have some clean flatweave (lint-free) dishtowels ready. Have clean screw bands ready, but it’s not necessary to heat them. Just make sure they’re not rusty or bent.

STEP TWO: cook the fruit

Make sure that there is plenty of liquid in the pan before you begin to cook. Add lemon juice (or your other acid) and a bit of butter. I add the butter to the fruit to reduce foam-up, which increases the yield of jam (thanks to my mum for teaching me this trick!) You can omit it if you hate the idea. Start with medium heat, and stir often at the beginning, so that no sugar will stick and burn on the bottom. Adjust the heat to bring the mixture to a violent all-over boil, and keep it there. When the color and/or texture changes, begin to check if the jam is ready.

But what about adding pectin?

Yes, some people do it, and a lot of recipes call for pectin. I avoid it when possible, because while you get a much higher yield from the batch, that comes because you use double the sugar. I find that the flavor of a jam is much more intense when I don’t add commercial pectin.

How to tell when jam is done

As the jam cooks, the texture of the liquid will change. Spoon some of the liquid (not the pulpy fruit) and hold the spoon up above the steam. Let it drop back into the kettle from the side of the spoon. At first (see left) it is light and thin. As it thickens, one drip will thicken into two, and if you cook it more, it will sheet off the spoon in a glob (see below). For my jam, I prefer the texture somewhere between the middle and the right picture.

Courtesy of National Center for Home Food Preservation, the photo depicts the Sheet/Spoon Test in determining whether jam or jelly made without added pectin is done.

The Wrinkle Test is more tactile. When you start to cook the jam, put a saucer or small plate in the freezer to chill. When you think the jam may be ready, put a little dab of the hot stuff on the chilled saucer, and put it back in the freezer for 1 to 2 minutes. Take your jam pot off the heat while you do this so it doesn’t cook down further. When the minutes are up, check the jam: when you push at it with your fingertip, do little wrinkles show on the surface? If you drag your finger through the blob, does the line stay and not fill back in? Line stays, it’s ready. If not, it needs to cook a bit more.

STEP THREE part 1: fill the jars

Line up your hot sterile jars on the counter near your kettle. Put a funnel in the closest one, and ladle hot jam into the jar just past the bottom of the funnel. Generally you’ll leave one-half inch of headspace.

Be careful! That jam is boiling hot, and so sticky that it will act like napalm – don’t let it get on your skin. Carefully move the funnel to the next jar, and repeat, until all your jars are full. NOTE: I always prepare 1 more jar and lid than I think I’ll need, just in case. Better to have one clean and ready, than to run out of space. If you have an odd bit left, you can put it in a bowl or custard cup, and just refrigerate it, planning to use it during the next week or so. In my house it would last about 2 days.

When all your jars are filled, wipe their rims with a clean damp cloth. Particles of food on the rim can mean that the jar won’t seal right. Cover each jar with a flat lid (rubber gasket down). Attach screw bands to each jar only until a point of resistance is met – that’s finger tight. Don’t screw them down as far as you can get them to go! 

STEP THREE part 2: seal the jars

As you start cooking your batch of jam, have your water ready, too. Now you have choices: will you process your jars in a traditional waterbath, ie that honking big kettle of boiling water? Or will you use one of the newer steam canners? Let’s look at the traditional waterbath method.

A big batch of jam, 9-14 jars, will need a big 20-quart kettle. For a medium batch of 5-7 jars a smaller 12 quart pot will do well. For a tiny batch, just use a deep saucepan. Fill the pot with about six inches of water, which will level out at 2 inches over the tops of the filled jars, once they are all in there. Start to heat this water while the jam cooks.

When the jars are filled and the lids and bands on, put them in this hot water one by one. A jar lifter is the perfect tool – don’t try to use tongs, and never handle a hot jar only by its lid or band; this can break the seal. Place the jars one by one in the water in the kettle, spaced evenly. The water should cover the jars by 2 inches – if it doesn’t, add more hot water until it does. Cover the canning kettle, and bring it to a rolling boil. Set a timer, the jars need to be processed in boiling water for 10 minutes. If the water stops boiling, bring it up to a boil again and re-start the timer.

After 10 minutes of boiling, remove the jars one by one from the kettle of water. Put them upright on clean dry dishtowels on your counter with 1 to 2 inches of space between each jar. Leave the bands alone! Don’t touch them, because it can interfere with the seal. Let the jars cool naturally. You will most likely hear a series of cheerful POPs as the lids snap sealed.

After the jars have cooled for 12 hours or so, test the seals. The simplest way is to press on the center of each lid. If the center of the lid does not flex up and down, the seal is complete.

What about that steam canner?

You need much less boiling water with a steam canner – only about 2 1/2 quarts. Place the jars on the rack inside the canner and cover with the lid. Bring to a boil, and when the temperature gauge shows that the works is up to temperature and steam is present, process the jars for 10 minutes (for 8-oz jars). After that 10 minutes has ended, let the jars sit in the steam canner undisturbed, and then remove the lid, use a lifter to move the jars to clean dry dishtowels, and let them cool naturally. You’ll still hear a series of cheerful POPs as the lids snap sealed.

Canning tools

Most hardware stores, some grocery stores, and just about all Meijer, Target and Wal-Mart stores carry canning supplies, including jars, lids, and some great tools. Invest in a set of canning tools once, and you’ll use them for years and years. One common utensil kit from the Ball corporation includes a funnel for filling the jars, a headspace gauge and air-bubble popper, and a jar-lifter, all for about $13: highly recommended! I also love my special canning ladle, which has a large capacity and can pour in any of 3 directions. The same company makes a 3-piece canning essentials kit that includes a funnel that slips over the jars, making for less cleaning of the rims. I use a silicone blossom trivet on the bottom of my pot so that water can circulate underneath the jars, though my mom used to use a clean waffle weave dishcloth for the same purpose.

Note: I do not have an Amazon affiliate link; I do not make any money from anything you might click on or even purchase. These are just tools that I use in my own kitchen. 

2 Comments

  1. Kelly Kolysko

    Thanks Maurita!! I will be reading your blog from now on!

    • I’m so glad! This may be the longest post on my blog … most of them are shorter.

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Welcome

I’m Maurita Plouff, and I write about cooking and preserving the local harvest in Southeast Michigan. Any recipe you find here is something I have cooked myself, and enjoyed, and think you might like too. I invite you to try the recipes, and leave comments.

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