Making Strawberry Preserves

By Joshua Bardwell, originally posted in May 2011 at Jack-Booted Liberal.

Today, I’m making strawberry preserves!

A caveat: Preserving/canning is easy and basically anybody can do it. That being said, if you do it wrong, you can make whomever eats your food seriously ill. If you want to start canning, find a complete set of instructions and follow them closely. This post is not intended to be a complete set of instructions, although it will contain some helpful tips. You can find instructions for canning all over the Internet. A good source of information is the University of Missouri Extension service. The boxes of pectin that you buy also often contain canning instructions. Follow them closely!

Step 1: Start your water boiling with your jars in it. Depending on how many jars you’re going to can, you may need a lot of water, so it’s good to start this going before anything else, so that the water has time to come to a boil.

The number of jars you need will depend on how much fruit you have to preserve. The recipe will tell you how much fruit you need per pint or per half-pint. My recipe, which I got from the back of my jar of pectin, says I need 1 2/3 cups of crushed strawberries per pint of preserves. I determine that I have a total of 9 cups of crushed fruit, so I divide 1.666 into 9 and determine that I am making 5.4 pints of finished preserves. I will need 5 or 6 pint jars.

Some instructions will tell you that you need to boil the jars in order to sterilize them. The Ball Book of Home Preserving disagrees with this. If you think about it, you’re going to process the closed jars after you fill them. That’s when sterilization occurs. Pre-sterilizing is unnecessary. The real reason, I believe, for pre-boiling your jars, is that it avoids temperature shock. If you take a room temperature jar and put it into a boiling water bath, the jar can crack. Any method of pre-heating the jars will work. Some people put them in the dishwasher. Some people even put them in the oven, although that takes longer, because air is a worse transmitter of heat than water. Since I’ve got to get the water boiling anyway, that’s how I prefer to pre-heat my jars.

There needs to be enough water in the pot to cover the jars by at least 1″ when they are full of preserves. Since the jars are empty when they go into the pre-boil, they displace less water than they will when they’re full, so I usually fill the pot just enough to cover the jars during the pre-boil, and then when I fill the jars, they displace enough water to raise the level to 1″ or more over the jars.

The pot you use for canning can be anything that’s big enough to hold the mason jars and have at least 1″ of water over the top of the jars. I have a huge pressure canner that I like to use, because it lets me can many jars at a time. Be aware, however, that with most forms of fruit preserves, you do not need a pressure canner, because they have sufficiently high acid levels to kill botulism spores. Any pot that will hold boiling water will work for high-acid canning, which is what we’re doing here.

You’ll also notice that I’m using a propane camp stove, even though I have a perfectly functional range top. The reason for this is that I have a glass-top electric range, and the weight of the canner and all that water might break the glass. Also, the propane stove puts out more BTUs than the electric stove, so it boils the water faster. A final benefit is that the propane stove can be put outside during the heat of the summer, which is when most canning goes on.

On a side note, I do a lot of camping, so owning a camp stove is a no-brainer, but it’s wonderful from a preparedness perspective as well. We recently had some bad tornadoes in the southeast, and some of my friends were without electricity (and, hence, their electric range) for a week. A propane camp stove would have gone a long way towards increasing their comfort. If you decide to go this route, I highly recommend buying an adapter that allows you to run your appliance off of a 20 lb propane tank. Most small appliances come with a fitting that attaches to a 1 lb tank. 20 lb tanks have a larger fitting that is usually used for gas grills and larger appliances. 20 lb tanks are better in that they are cheaper per pound and they are refillable, so you don’t have the waste of the empty 1 lb tanks. You can find the adapter in the camping section of some Wal-Mart stores, or online (of course). Here’s an example of such an item:

Coleman High-Pressure Propane Hose and Adapter

That item has an attached extension hose, so it’s an adapter and an extension. If you just want the adapter (to attach to the hose that came with your appliance), you can buy that as well, and it’s about 1/3 the cost. Just be careful that you’re buying the right adapter, as there are several different kinds (for example, you don’t want the one that will let you run your big gas grill off a small 1 lb adapter. You’re trying to go the other way, and run a small appliance off a big tank.

Step 2: The next step is to prepare the fruit that’s being preserved. In this case, that involves hulling strawberries and then rinsing them. I’ve got compost on the left for the tops and a colander on the right for the rinsing. I like using a grapefruit spoon to hull strawberries, but Issa prefers a knife.

Step 3: Next, I mash the strawberries with a potato masher. I like to have a lot of solid fruit in the preserves, so I don’t mash them very much. After mashing, I pour them out into a measuring cup, to keep track of how much I’ve got, so I know how many jars I need and how much pectin and sugar to put in.

Step 4: Pour the mashed fruit into the pot and add the appropriate amount of pectin. The recipe will say, “for each pint of preserves, you need X amount of fruit, Y amount of pectin, Z amount of sugar,” and so forth. I’ve got the strawberries in a very tall pot because sometimes when you add the sugar, they froth up a lot, and I’ve had it overflow some of my smaller pots.

A word on pectin. Pectin is a chemical that occurs naturally in plants. It is added to preserves, jams, and jellies as a gelling agent. It’s what causes the preserve to “set up” and be thicker than a sauce. You can make no-added-pectin jams, in which case you boil down the fruit until it naturally thickens. Adding pectin means that you don’t have to cook the fruit as long, which makes for a fresher taste and faster cooking. Adding pectin also increases the odds of successful set. That being said, it’s not absolutely essential that a preserve sets. I’ve eaten many a piece of toast with runny jam on it, and it was just as delicious, if a little bit harder to manage.

There are at least two types of pectin: full-sugar and low/no-sugar. Full-sugar pectin requires a lot of sugar in the recipe to set the preserves—perhaps 1 to 1.25 cups of sugar per cup of fruit. Low-sugar pectin is capable of setting the preserves with less sugar in the recipe—1/2 cup of sugar per cup or less. I prefer low-sugar jams for several reasons. First, sugar is the most expensive part of the preserves for me, since I grow my own fruit. Using less sugar means cheaper preserves. Second, when I eat preserves, I want to be eating fruit first and sugar second, both for health and flavor reasons. That being said, I have made strawberry preserves with very little sugar, and I didn’t like the taste at all. Much too tart! I find about 1/2 cup sugar per cup of fruit to be about right.

Step 5: Bring the mixture to a boil over high heat. As you do this, the strawberries will release a lot more juice. Keep stirring to keep the mixture from scorching on the bottom and in the corners of the pot. It is necessary to boil the mixture vigorously to thoroughly cook the pectin. Once the mixture reaches a full boil that cannot be stirred down, pour in the sugar. Continue stirring until it comes back to a full boil that cannot be stirred down and boil for one minute. Remove from heat.

During this step, be careful not to let the boiling mixture splash up onto your hand or arm. Boiling hot sugary sticky mess makes unpleasant burns.

Step 6: Remove the empty jars from the boiling water and fill them with the hot fruit mixture. A canning funnel (pictured above) is very useful for this. A canning jar lifter is also very useful for handling the hot jars. One note: when you lift the empty jars out of the water bath, they will be full of boiling water, which you will need to pour out. Be very careful not to accidentally pour it onto your hand or arm. Sounds obvious, but it’s a common mistake.

When filling the jars, it’s important to leave enough headspace (empty space at the top of the jar). The recipe will specify the amount of headspace required.

Step 7: Put on the lids and screw down the rings tightly. The cans are now ready for processing

Step 8: Using the can lifter, return the filled cans to the boiling water bath. Cover it (optional, but it makes things go faster) and return it to a full boil. Once the water returns to a full boil, start the timer, and process (continue to boil) the cans for as long as the recipe says to.

Keep in mind that various things affect processing times. Most notable are altitude (higher altitudes have to process longer) and the size of your jars. If your recipe says to process for 15 minutes in pint jars, you will need to process longer if you elect to use quart jars. It’s best to follow the recipe closely. Remember, we’re talking about food poisoning here!

After processing, remove the jars from the water bath and set them on the counter to cool. As they cool, the lids will “pop”. What’s happening is that the air remaining in the jar (the headspace, remember) is cooling and, as it does, it is contracting, creating a vacuum inside the jars. The lids “pop” down as this happens.

After 24 hours, remove the bands and check the lids. The centers should all be popped down and the lids should be tightly stuck to the jars. If any of the jars did not seal properly, you can simply place them in the refrigerator and consume them within the next few weeks. You do not need the bands anymore; the lids should be quite securely stuck to the jars. If you store the jars with the bands on, they can rust and stick to the lid and the jar, making it very difficult to open the jar and also leaving rust on the threads that is a pain to clean off. Also, one of the signs that a jar has gone bad is that a lid comes un-stuck. What happens is that, if the sterilization process went wrong somehow, micro-organisms inside the jar will start to multiply and feed, and they will produce gases as they do. This will spoil the vacuum in the jar and cause the lid to pop off. If you come across a jar on the shelf with a loose or popped lid, don’t eat it! Throw it out! But if you keep the bands on your jars, you might not notice this.

The process described herein is basically the same for all fruit preserves. The only difference is the ratio of fruit, pectin, and sugar. If this kind of thing interests you, I also heartily recommend looking into canning pickles, which is another high-acid food that’s incredibly easy to do. Maybe I’ll write a post about that in the future.