How to Sterilize and Process Jars for Preserves

For those who are coming late to this series on homemade preserves, you might want to read the two previous posts. 1. Essential Tools for Making Preserves  and 2. Key Ingredients for Great Homemade Jams and Jellies. For those, like me, who just want to jump right in, the only point you really need to know that any preserve recipe you use should be fron 1989 or later. Why? Read the second post in the series to find out. Not only will you be making safe jams, you could win a round of Trivial Pursuit one day.

How to Sterilize and Process Jars for Preserves

Sterilizing Jars

Because you will be processing the preserves in a water bath, you don’t need to sterilize the jars. This will happen during the processing — and since you’ll be using a post-1989 recipe, that is a given. Right?  Technically, you need to sterilize the jars if they will be processed for less than 10 minutes, but I have never seen a modern recipe that doesn’t allot at least this amount of time, so let’s move on.

Regardless, all jars should be clean and warm to prevent them from cracking when the hot jam is added. Many people wash them in hot, soapy water and then heat them in the water they’ll use for processing. Cookbook author and preserving expert Jennifer Mackenzie has a great trick. She puts her jars through the dishwasher on the sterilization cycle and leaves them there with the door closed until she’s ready to fill them.

At the risk of repeating myself, all jars should be proper preserve jars (often called mason jars) that are free of chips or cracks. And while we’re at it, wash a couple of extra jars, just in case the recipe provides more than expected.

Outdated Sealing Methods

You likely know someone who doesn’t bother to process their preserves in boiling water and has never had an issue. I’m not about to argue with them. However, I’m not about to suggest you do anything less than what’s safe. The following methods may be popular, but they are not recommended.

• Paraffin seals: Although I survived the wax-sealed jams of my childhood, is probably the worst way to seal jam outside of leaving it out on the counter for the fruit flies to fight over. The paraffin seal can actually trap air between the wax and the jam, which makes a lovely breeding ground for mould, yeast, and bacteria. Don’t use wax seals. Ever. Even if it looks pretty and has a fetching vintage feel. Don’t. Just don’t. I’ll feel better if you promise not to. Cross your heart.
• Turning hot jars upside down: Airborne microorganisms can sneak in when you’re filling the jars. I used to think this was what I called CYA Paranoia — until I found a cat hair in my jelly. Thanks to the boiling water bath, that cat hair is shiny and germ-free.
• Letting the heat of the jam seal the jar: Like the previous point, this isn’t quite up to food safety standards. Besides, if you’re putting all that money and time into preserves, you might as well do it right.

How to Process Preserves in a Boiling Water Bath

While you can use a pressure canner, that is over-kill for jams and jellies. This method works and can be done with a stockpot or Dutch oven.

1. Wash your jars, lids and rings.
2. Place a canning rack (or alternative) in the bottom of a stock pot, Dutch oven or canner. Place the jars on the rack and fill the jars and canner with hot water to about 1 inch above the jar top. Cover and bring the water to a simmer.
3. Make your jam or jelly. The recipe should be post-1989, have these key elements and call for a boiling water bath for processing.
4. About 5 minutes before you’re ready to fill the jars, place the lids in the hot water to soften the rubber.
5. Fill jars with hot jam, using a funnel if you have it, according to the recipe directions.
6. Run the Bubble Tool around the inside edge to release any trapped air and use the stepped edge to measure the headspace. The recipe should tell you how much room to leave, but if it doesn’t the standard rule is 1/4 inch for jams and jellies, 1/2 inch for pickles.
7. Wipe any spills with a clean damp cloth. Spills on the side of the jar are merely sticky, but jam on the rim can prevent the lid for forming a proper seal.
8. Use the Magnetic Wand to remove the lid from the hot water and centre it on the jar.
9. Screw the ring on until it is finger-tight. It needs to be a bit loose to allow air to escape.
10. Use the canning tongs to set the lidded jars in the canning pot of hot water. Place the jars upright in a single layer on the canning rack. Do not stack them. Make sure the jars don’t tip or touch each other. You might have to remove some of the water, but make sure the  jars are covered with a good inch of water.
11. Cover and bring the water to a boil. Start the timing once the water reaches the boiling point.  The timing of the water bath depends on the size of jar and the density of the food being preserved. Elevation also plays a role in the timing. See this chart on Canning at High Altitudes if you live more than 1,000 feet above sea level.
12. Turn off the heat and let the jars sit in the hot water for 5 minutes or so. Trying to pull hot jars out of boiling water is just asking for trouble. Once the water dies down, use canning tongs to remove the jars. Place them on a heat-resistant surface where they won’t need to be moved for 12 to 24 hours.  While they cool, listen for a pop as the lids seal. If you can’t hang around to listen or lose count, you can tell if the jars are sealed by pushing the centre of the lid. It should be sucked down. If it gives, the jar didn’t seal.

What to do if a jar doesn’t seal

Don’t panic. This happens from time to time and is a welcomed excuse to taste the jam. Store improperly sealed jars in the refrigerator and eat them right away. Alternatively, you can freeze them for later. Just remember to eat these jars first and not give them as gifts.

While you’re at it, ditch the ring and replace it with a plastic lid as a sign the jar has been opened or compromised. You can use the ring again, but throw out the lid. Replacement lids are readily available anywhere you buy mason jars. (Note: I have never had a jar fail to seal during a water bath. I’m just putting this information here in case it happened. If it happens, please email me. I’d be really curious to know the circumstances.)

Do you have any tricks with the boiling water bath?

Up Next: How to Tell if Jam or Jelly is Set