Water bath preserving
A complete beginner's guide to preserving food safely at home
If you've ever stood in front of a bench covered in tomatoes wondering what on earth you're going to do with all of them, this is for you.
Water bathing is one of the simplest ways to preserve food at home. It's how I put up passata, jams, pickles, chutneys, and fruit every year. Jars that sit on the shelf for months without a fridge. No special equipment. No complicated science. Just heat, glass, and a bit of patience.
I've been doing this for over 20 years and I still get a quiet thrill pulling a jar of passata off the shelf in the middle of winter, knowing it came from our garden in February. That's the whole point, really. You grow it, you cook it, you put it away. And months later, it's still there.
This guide covers everything you need to know before you start. If you've never water bathed anything before, read the whole thing through once. It'll make the first time feel a lot less daunting.
What is water bath preserving?
Water bath canning is a way of preserving high-acid foods by sealing them in glass jars and submerging them in boiling water for a set time. The heat drives air out of the jar, creates a vacuum seal, and kills the microorganisms that would otherwise cause spoilage.
Done properly, water bathed jars are shelf stable for 12 months or more. No fridge needed.
It works for things like tomatoes and passata, jams and marmalades, fruit in syrup, pickles, chutneys, relishes, and lemon curd.
Why acid is everything
This is the most important thing to understand, so I'm putting it right up front.
Water bathing is only safe for high-acid foods. That means a pH of 4.6 or below. Acid is what prevents the growth of Clostridium botulinum, the bacteria responsible for botulism. Low-acid foods like plain vegetables, meat, or beans cannot be safely water bathed. They need pressure canning, which is a different process entirely.
If you remember one thing from this guide, make it this.
A note on tomatoes
Modern tomato varieties have been bred sweeter over the years, which pushes their pH closer to the borderline. So you always add citric acid powder when preserving them. A quarter teaspoon per litre jar, added directly into the jar before the food goes in. It's flavour-neutral. You won't taste it. But it's non-negotiable for safe passata.
You can get citric acid powder from most supermarkets or bulk food stores. It's cheap and it lasts forever.
What you need
You don't need fancy gear. Most of this you probably already have in the kitchen.
- A large stockpot or Fowlers Vacola unit. Deep enough to cover your jars by at least 3 to 5 cm of water. If you're just starting out, a big stockpot works fine.
- A jar rack or a folded tea towel. This goes in the bottom of the pot to keep jars off the direct heat. A tea towel folded up does the job perfectly.
- Glass preserving jars with lids. Mason jars, Ball jars, Fowlers Vacola, or similar. Lids need to be new or in perfect condition. If there's any rust or damage on the seal, don't use it.
- Jar lifter or tongs. These jars are extremely hot. Don't try to handle them with bare hands or a tea towel. A proper jar lifter makes your life much easier.
- A ladle and wide-mouth funnel. For filling jars cleanly without getting food all over the rim.
- Clean cloths. For wiping jar rims before you seal them.
- Citric acid powder. For tomatoes and passata. A quarter teaspoon per litre jar.
- A timer. Processing time is precise. Don't guess it.
The process, step by step
1. Sterilise your jars
Wash jars, lids, and bands in hot soapy water and rinse well. Place jars upright in your pot or oven at 120 degrees for 15 minutes. Keep them hot until you're ready to fill. Cold jars can crack when hot food goes in, and I've learned that the hard way.
2. Prepare your food
Cook or prepare your recipe as directed. Work cleanly. Food should be hot when it goes into the jars. This is called hot packing, and it's the standard for most preserves.
3. Add acid (passata and tomatoes only)
Add a quarter teaspoon of citric acid powder per litre jar directly into the jar before adding your food. For half-litre jars, use an eighth of a teaspoon.
4. Fill the jars
Ladle hot food into hot jars, leaving the correct headspace. That's usually about 1 to 1.5 cm for most preserves. Headspace is the gap between the food and the lid. Too little or too much will affect your seal.
5. Remove air bubbles
Run a clean knife or chopstick around the inside edge of the jar to release any trapped air bubbles. Top up to the correct headspace if needed.
6. Wipe the rim
Use a clean damp cloth to wipe the rim and threads of each jar. Any residue, even a tiny bit, can prevent a proper seal. This step matters more than you'd think.
7. Seal the jars
Place lids on jars and screw bands on fingertip-tight. That means firm but not forced. Over-tightening prevents air from venting during processing.
8. Process in the water bath
Lower jars onto the rack in your pot. Make sure they're covered by at least 3 to 5 cm of water. Bring to a full rolling boil, then start your timer. Process for the time specified in your recipe. This varies by food type and jar size, so follow what your recipe says.
9. Remove and rest
When the timer goes off, turn off the heat and remove the lid. Wait 5 minutes, then lift the jars out with your jar lifter and place them on a folded towel. Leave 3 to 5 cm between each jar. Do not tilt them, press the lids, or move them around for 12 to 24 hours. Just leave them alone. I know it's tempting.
10. Check the seals
After 12 to 24 hours, press the centre of each lid. A properly sealed lid will be concave, curved slightly inward, and won't flex or pop when you press it. If a jar hasn't sealed, put it in the fridge and use it within a week, or reprocess it within 24 hours.
Storage and labelling
Store sealed jars in a cool, dark place away from direct sunlight. Label every jar with what's in it and the date you processed it. I use a permanent marker straight on the lid because I gave up on pretty labels years ago.
Most water bathed preserves are best used within 12 months. Not because they necessarily go off, but because quality starts to decline over time. Colour fades, texture softens. They're still safe, just not at their best.
Once you open a jar, treat it like fresh food. Into the fridge, use it up.
When to throw it out
Throw out any jar that shows a bulging or unsealed lid, spurting liquid when you open it, an unusual smell, mould, or cloudiness in something that should be clear.
When in doubt, throw it out. Do not taste-test to check. This is not the place to be brave.
Always use tested, published recipes from trusted sources. The USDA Complete Guide to Home Canning, Ball Blue Book, or Fowlers Vacola are all reliable. Processing times are specific to the type of food, the acidity, the jar size, and your altitude. Never shorten them.
Water bathing isn't complicated
It's just methodical. Once you've done it a few times, it becomes second nature. The first batch always feels a bit nerve-wracking, and then you hear that first lid pop and seal while you're cleaning up, and you understand why people have been doing this for generations.
Start with something simple. Passata is a great first project if you've got tomatoes coming out of your ears in summer. Jam is forgiving. Pickles are quick.
You don't need to preserve everything. You just need to start somewhere.
If you found this useful and it's your kind of thing, drop your email below.
I'll be sharing preserving recipes, seasonal cooking ideas, why natural fibres mean so much to me, and everything i've picked up from 26 years of growing and cooking my own food in tasmania. not filler — just real, useful stuff from someone trying to live with a little more purpose.