Boiling Water Bath Canning – basic principles

This article should serve as a handy reference point for anyone who is unsure how to can by using the Boiling Water Bath, or Hot Water Bath, method. You might want to have a read of my article on setup costs as well.

The technique I am describing here is only for products that can be dealt with in a hot water bath process, or “high acid foods”. A few examples of high acid foods are jams, jellies, pickles, relishes, and chutneys. Foods such as vegetables, meat, fish, stocks and broths are “low acid foods” and need to be dealt with by pressure canning, which I will deal with in a separate article.

First, you need a boiling water bath canner:

canner with jars

Canner and jars

Next you need some jars. Exactly what size you use will vary depending on recipe. Jelly jars hold 1 cup(8 US fl oz)/250ml (centre of rack in picture above). Pint jars hold 2 cups/500ml (centre left and right of rack in picture above). Quart jars hold 4 cups/1 litre (back of the rack in picture above). I know that these are not exact conversions of US fl oz to ml, but the volume difference between the metric and American style jars doesn’t make any difference for our purposes – the recipes and the processing times are the same.

Third, you need lids and bands. New jars come with lids and bands, but you should pick up extra lids when you can get them at a good price. The bands are reusable for many canning sessions – they only need to be discarded if they show signs of rust or corrosion.

And finally, you need something to put in the jars – the “jar contents”.

PREPARATION STEPS

JARS
To start a boiling water bath session, first clean the jars you are going to use. Running them through the dishwasher works well; if you don’t have a dishwasher you can wash them in the sink. Once they have been cleaned, put them in the rack, place the rack in the canner, then fill the canner with hot water (from the tap is fine) until the jars are covered to about a finger width above the rims. Once the jars are covered with hot tap water, put the lid on the canner, put the canner on the hob, and set it to a medium-low temperature.

This is all before you do anything to the “jar contents”. You are aiming to have the jars at a good hot temperature before filling them with the “jar contents” – too much of a temperature difference between the jar and the contents leads to thermal shock, also known as “glass shrapnel and incendiary contents spread across the kitchen”. Thermal shock is generally considered A Bad Thing(TM) and is definitely to be avoided.

Once the “jar contents” are starting to cook, increase the heat under the canner with the aim of getting it to a full boil once the “jar contents” are ready. It’ll take you a little practice to know exactly when to turn the heat up, but don’t sweat it too much – you can keep the “jar contents” nicely hot for a few extra minutes if needed, and it doesn’t really matter if the empty jars are boiling for longer than needed.

LIDS
Give the lids a good clean with plenty of soap and hot tap water and then rinse thoroughly. I have seen many people saying to boil the lids and then keep them in the hot water straight after boiling, but according to the Ball Complete Book of Home Preserving (which I cannot recommend strongly enough – it is absolutely essential for a home canner), all that is needed is to keep them to a simmer – 180F/82C.

Once your lids and jars are ready, you can ladle in your jar contents (the pickles, jam, relish, etc.) and then seal the jars.

SEALING THE JARS
Once each jar is filled to the appropriate level (usually within 1/4 to 1/2 inch of the top of the jar depending on the recipe) you should wipe off the rim of the jar to make sure that there is nothing on the rim to interfere with a proper seal. Use a paper towel sprayed with a 50/50 mix of white vinegar and water to wipe off the rim. Lift lids out one by one and place on the rim. Screw down the bands to “finger tight”: use your fingertips to screw the lid down until you can’t tighten it any more, but do not tighten the lid as tight as you possibly can. The purpose of this step is to secure the lid on, not to seal it completely – there needs to be a little looseness in the band to allow air to escape, but equally you don’t want water to get into the jar. The jar seal comes from the vacuum you will create in the water bath stage.

HOT WATER BATH
Once your jars, lids, and “jar contents” are ready, it’s time to put them on the wire rack and lower them into the hot water, which should be at a boil at this stage. You want to see a stream of bubbles come up from the jars.

Place the lid on the canner, and process for the amount of time specified in the recipe. Once the processing time is up, take the pot off the heat, take the lid off the canner (carefully! you don’t want to get caught by the steam!) and leave for 5 minutes before lifting the rack out of the hot water and hooking it over the edge of the canner. Use your jar lifter or tongs to take the jars out of the hot water to cool.

COOLING THE JARS
The best way I have found to cool jars without having any danger of thermal shock (hot jars and cool countertops do not mix) is to use a cookie rack. This allows free air circulation around the jars without putting them onto any surface which could turn them into jam bombs.

Leave the jars overnight; the next day you can take the screw bands off and test the seal.

TESTING THE SEAL
Testing the seal is easy. If you can lift the jar up by the lid, the seal is good. If you can’t, the seal is bad! If a jar didn’t seal properly, treat it as an eating jar and just finish the contents within a few days, or as normal (pickles last longer than jams when opened).

You were waiting for me to say what the jar contents are? Well… that’s up to you. Go for it!

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6 Responses to “Boiling Water Bath Canning – basic principles”

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    Our raspberries are just starting to ripen. Doesn’t raspberry jam sound good with the jars sealed in a hot water bath. Thanks for a great article.

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    Raspberry jam, or even pie filling, sound divine! (Check around the site for pie filling and jam recipes and just substitute the appropriate fruit).

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