Canning fruit is actually quite easy and doesn't take a lot of time. But making sure you do so safely can seem intimidating.
Once you know what is required to safely can fruit, you'll have the confidence to do it yourself. I'm here to explain, in depth, what is required to safely can jams, jellies, and fruit preserves.
Side note: I'll refer to canning fruit jams, jellies, and preserves simply as 'jams' or 'jams, etc' (so as not to repeat those three types of canned fruit over and over and over...).
This article covers:
- Equipment & alternatives
- How to can safely
- Does sugar act as a preservative?
- Acid is required
- Creating a vacuum seal
- How long can you store jam?
- Cookbooks & other resources
- A note on Covid pricing
What equipment is needed?
You don't need a lot of equipment and probably have most at home already.
- Canning jars (mason jars, etc), lids, and bands
- A large pot to boil water
- A rack* of any kind
- A funnel*
- Can lifter* (or tongs)
If you don't have a rack, funnel, or can lifter, you can make your own.
Water bath canning vs pressure canning
Water-bath canning refers to boiling jars in a pot of water. This works on acidic foods, like jams, jellies, and fruit preserves (and tomatoes). That's because high acid levels act as a preservative against mold and bacteria.
Low acid foods, like green beans and most vegetables, need extra help to eliminate harmful mold and bacteria. Higher levels of heat provide that needed help. Since the temperate of boiling water caps out, we turn to pressure cookers to reach the necessary higher temperatures.
Are jars reusable?
Mason jars (and other canning jar brands) are reusable. Throw them in the dishwasher or give them a good thorough hand-washing. The water-bath process will re-sterilize the jars.
The bands are also reusable, but make sure they haven't rusted.
Are lids reusable?
Lids are not reusable. They need to be discarded and new ones need to be purchased every time. There's a material on the lids that helps seal them to the jars. It's only good for one-use.
You can sort of think of it like glue. Once you use it and it dries, you can't peel it off and stick it to something else.
What are the best sizes for jars?
There are several good options, it depends on your use.
- For gifting: I use 4 oz jars almost exclusively for gifting. They are adorable, the jam goes further, and I can gift 'sets' of different flavors. (As of mid-October, you can still get these jars affordably on Amazon for $1 per jar).
- For cheese boards: I also love 4 oz jars for cheese boards because you don't need much more than that. When the same knife inevitable cuts some cheese then is dipped into the jar, I also don't have to worry about contamination - the jar will be empty by the end of the night.
- For personal use: 4, 8, or 12 ounces all work and it depends on how quickly you go through jam. The typical store-bought jam jar is usually 8 ounces, for reference. (shop for 8 and 12 ounce jars on Amazon).
Most jam-type recipes suggest not to go over a pint jar (16 oz) as the boiling times change and the recipes haven't been tested for safety above that size.
How to safely can jams
The main two ways you prevent mold and bacteria growth (spoilage) when canning fruit jams (etc) is with acid and heat.
Acid acts as a preservative
An acidic environment prevents mold and bacteria from growing. Most fruit is naturally high in acid. Even with natural acidity, jam (etc) recipes also add extra lemon juice (highly acidic) to ensure the acid levels are high enough to be safe.
Boil to sterilize & seal
Jam-filled jars need to be submerged in boiling water for a specific amount of time (see processing times chart) to safely kill mold, yeast, and bacteria.
Some recipes might specify that you sterilize the jars by first boiling them (empty) in the water-bath. This won't hurt. But the USDA says this is unnecessary as long as you process jars for at least 10 minutes in the boiling water.
However, jars do need to be warmed so they don't break when filled with the hot jam. This can be achieved by running them under hot tap water or placing in the boiling water-bath briefly before filling.
Who am I to tell you this is all that's needed to safely can jam? I'm not a food scientist afterall, and you can't believe everything you read on the internet.
What I've done is thoroughly researched the topic and consulted trusted sources (like government branches and university research offices). I also cite and share sources in case you also want to read them.
The USDA (United States Department of Agriculture) is one of these trusted resources. Their "Principles of home canning" publication lists proper canning practices. For jams and jellies, that includes (my comments in italics):
- Carefully selecting and washing fresh food (don't can moldy food)
- Hot packing (boiling the jam and then pouring it into jars)
- Adding acids (like lemon juice)
- Using acceptable jars and self-sealing lids
- Processing jars in a boiling-water bath for the correct period of time
- Store jars below 95 degrees F
One thing that the USDA does not list as a requirement for safe canning is sugar. But many resources say things like "sugar acts as a preservative," making this quite confusing.
Since I want you to be very confident in what you can, let's look at this more in depth.
Does sugar act as a preservative?
This can actually be a confusing topic because so many (trustworthy) sources use phrases like 'sugar acts as a preservative.' Sugar does help preserve the color and texture of the fruit, but is not necessary to prevent food spoilage for canning jams and jellies.
There are times when sugar can be a preserving agent to prevent food spoilage. However, the levels used in jellies, jams, and preserves isn't high enough to prevent them from spoiling during the canning process.
Ball's Book of Canning and Preserving clarifies this even further, saying, "Sugar has preserving properties as it replaces some of the water in fruit, but the amount used in canning is just enough to help delay spoiling once jars are opened." (my emphasis)
Their website reiterates this point, and goes on to say that sugar substitutes can even be used.
To give you even more confidence on this topic, Michigan State University has an excellent article, "Home canning without sugar" that repeatedly states, "Sugar is not needed to prevent spoilage."
They continue, saying, "With that in mind, you may want to do some experimenting to find what you really like when it comes to canning with no sugar. Only experiment with the amount of sugar added, or not added – nothing else."
Ball also reiterates that "Low-sugar / no-sugar fruit jams and jellies preserve just as safely but need to be consumed quickly once opened." Because of this (and the fact that I don't go through jam quickly), I make them in small 4oz jars like these.
Are there any downsides to low / no-sugar jams?
To be clear: Acid and heat do all of the work to prevent your canned jams from spoiling.
While safe to use less sugar, there are some minor downsides to canning reduced sugar jams and jellies. The main thing to know is that pectin (the gelling agent) needs enough sugar to properly gel.
There are a few other things to consider before reducing the sugar:
- Regular pectin might not properly gel (see note)
- Bright color might fade or turn to a slightly off color (see note)
- Might not be as 'clear' (could look slightly cloudy)
- Can have a softer texture
- Might not have as firm of a set
- Once opened, it can have a shorter shelf life in the fridge (weeks instead of months) (source: Ball Book of Canning & Preserving)
Products like Ball's low / no-sugar pectin is created specifically to work with less sugar. The pectin will still gel properly and the added Calcium Ascorbate retains the fruit's color.
Acid is required for safe canning
This is the part of the jam recipe you need to take seriously. If the jam doesn't have enough acid, bacteria and mold can grow inside the canned jar.
There are two parts to never alter in a recipe: the type of fruit and the amount of added acid.
Fruit's natural acid
Some fruits are high in acid, like apples or strawberries. Other fruit are lower in acid, like figs. Recipes take this into account and add enough acid to make sure the fruit is safe to can.
You should not swap one fruit for another type in a recipe (unless specific instructions are given).
Jam recipes also call for added acid, usually in the form of lemon juice.
Always use bottled lemon juice because the amount of acid is very consistent. Acid from freshly squeezed lemons varies enough that the juice might not be acidic enough for safe canning.
One piece of fruit might be more acidic than another because acid levels drop as fruit ripens. The specific amount of added acid is calculated to make sure it's safe to can, even with the varying levels of acidity within a specific type of fruit.
Always use the amount of added lemon juice (or other acid) specified. Never less.
Creating a vacuum seal
The last thing you need for safe canning is a vacuum sealed jar. This process happens naturally when boiling the jam-filled jars.
Three things work together to create the vacuum seal: leaving headspace, finger-tightening bands, and the cooling process.
Headspace is the empty space (a gap) left at the top of the jar. Most jam recipes call for leaving ¼" of empty space at the top.
Headspace allows for the contents of the jar to expand when boiled in the pot of water. This pushes out air, and when cooled, creates a vacuum seal.
Lids & metal bands
The rim of the jar needs to be wiped clean with a damp cloth before placing the lid on it. If there is jam on the rim, it can compromise the seal.
The metal bands should be finger-tightened. They shouldn't be loose, but they also shouldn't be super tight. As the jars are boiled, air escapes from within.
The air needs to get out from under the lid, which is why it needs a little wiggle room from the band not being fully tightened. It needs to be loose enough to let air out, but tight enough that water doesn't get in.
This is hard to describe, but here's my best shot: I tighten the band until it stops turning. I imagine a 2 year old could take that band off with minimal effort.
Boiling for specified amount of time
As long as the jars are 1 pint or smaller, you can process (boil) them for the time listed in the chart below (source: USDA guide 01 and The All New Ball Book of Canning and Preserving). Higher elevations require longer processing times.
|0 - 1,000 ft||10 minutes|
|1,001 - 3,000 ft||15 minutes|
|3,001 - 6,000 ft||20 minutes|
|6,001 - 8,000 ft||25 minutes|
|8,001 - 10,000 ft||30 minutes|
Cooling the jars & getting the vacuum seal
Recall that contents expanded when boiled and pushed out some of the air at the top of the jar. Once jars are removed from the hot-water bath to cool, the contents contract.
But since air can't get back in at this point, it creates a vacuum seal. As this happens, you'll hear the typical 'pop' from the lid as it gets pulled down and seals.
It's important to not fuss with the jars while they cool, so you don't accidentally interfere with the vacuum sealing process by letting air back in.
How long can I safely store my jam?
Canned jams, jellies, and preserves can be stored in your pantry for a year. The USDA (Principles of Home Canning) specifies that the jars need to be stored below 95 degrees F.
This means you shouldn't store your jars near a furnace, pipes, an un-insulated attic, other appliances, or in direct sunlight.
Don't store in damp conditions either, as that can corrode the metal lids and break the seals.
Once opened, full-sugar jams (etc) last about a month in the fridge. Low sugar jams won't last as long once opened.
Canning books & resources
- Ball Book of Canning & Preserving: I own this book and every recipe I've made has turned out great. It starts by explaining canning basics, then moves on to various types of canning, from jams to pickles. Each section includes specific recipes, as well as chart to help you customize recipes. They also include low-sugar options for many fruit-based canning recipes. (Read the full review)
- Foolproof Preserving (by America's Test Kitchen): I also own this book and like the scientific approach and explanations. I've tried several recipes and they are excellent. I also like that they offer some recipes that don't use added pectin and instead rely on the fruit's natural pectin.
- Canning sets are really handy, especially the funnel that fits perfectly into the jars (double check that it works for regular vs widemouth jars). The jar lifters help as well. Neither of these have to be high quality, fyi.
- Ball's canning website (FreshPreserving.com) has a great resource to customize your own jam recipe. Their pectin calculator is meant to help you figure out how much pectin you need for any of their pectin products (like Classic, liquid, or low / no-sugar). But they also have recipes for each fruit (which downloads as PDFs, but they are hidden gems of information).
A note about canning jar prices during COVID
Mason and Ball canning jars, and lids, are extremely hard to find right now. I suspect people are stuck at home and trying new things, like canning, and I'm really excited for all of those people getting into it.
If you want to spend extra money, you can still find some supplies on Amazon, though vastly overpriced. Jar and lid sets normally cost less than $1 per jar.
I've compiled a price list for what canning supplies should cost, along with a few resources that are still selling them at fair-ish prices.