Pressure Canning in New Zealand: Is It Safe to Bottle Vegetables?
Updated October 2026
Beans, corn, pumpkin, kūmara and meat can never go through the overflow method or a water bath. They need a pressure canner, and in most New Zealand kitchens the freezer is the safer place for them.
Vegetables and meat cannot be bottled safely with the overflow method or a pot of boiling water. New Zealand Food Safety names low-acid foods such as asparagus, green beans, beetroot, corn and potatoes as the most common source of home-canning botulism. The only home method with tested times for them is a pressure canner used to a USDA process. If you do not have one, freeze the glut, or pickle it in vinegar from a tested recipe.
The risk in a sealed jar
Botulism comes from a toxin made by Clostridium botulinum, a soil bacterium that survives boiling as a spore. A sealed jar of low-acid food with no air is where the spore can grow. New Zealand Food Safety says adult symptoms appear within 12 to 36 hours: double or blurred vision, muscle weakness that spreads down from the head, nausea, vomiting and trouble speaking or swallowing. The illness can last weeks or months.
The dividing line is acid. Jars at pH 4.6 or below (fruit, tomatoes with added acid, vinegar pickles) are safe in a boiling water bath. Anything less acidic has to reach about 116°C right through the jar, which takes steam under pressure.
Low-acid foods that need a pressure canner
Green beans, runner beans, broad beans, peas, sweet corn, carrots, beetroot (unless pickled), potatoes, kūmara, pumpkin, mushrooms, asparagus, and every meat, poultry, fish and stock. Mixtures count too: a pasta sauce with mince or a soup with vegetables is low acid, even if it contains tomato.
Why the overflow method is not on our list
Many New Zealand recipe books still teach overflow bottling: boiling fruit and syrup poured into hot Agee jars, filled to overflowing and sealed. No food safety agency has published tested times for it. The USDA, the only body that has tested home methods, lists open-kettle canning (filling hot jars and sealing without processing them afterwards) as not recommended because it does not prevent all spoilage. For fruit, a boiling water bath with tested times is the safer method. For vegetables and meat, neither is safe.
Our take
A pressure canner in New Zealand usually means importing a Presto or All American from Australia or the United States, and paying for the shipping. Blanched beans, corn and pumpkin keep for months in a chest freezer. Unless you plan to bottle meat or stock regularly, the freezer is the better buy.
Using a pressure canner: the tested steps
From the USDA Complete Guide to Home Canning (2015). These are the steps the times were tested with, so none of them is optional.
- The canner: it must hold at least four US quart jars. Do not can in an electric multicooker; the National Center for Home Food Preservation says no tested process exists for one.
- The jars: USDA tested Mason-type jars with two-piece self-sealing lids (Ball and Kerr are the usual makes). If you use preserving jars made for overflow bottling, check the maker rates them for pressure canning.
- The water: 5 to 8 cm of hot water in the canner (2 to 3 inches) unless the recipe says more. The jars are not covered.
- Venting: lock the lid with the vent open and heat until steam streams out steadily. Let it run 10 minutes, then close the vent. Air left inside makes the canner cooler than the gauge says.
- Timing: start the clock when the target pressure is reached. If it drops below the target at any point, get it back up and time the full process again from the start.
- Cooling: turn the heat off and let the pressure fall by itself. Once it reads zero, lift off the weight, wait 10 minutes and open the lid away from you.
- Resting: leave the jars undisturbed for 12 to 24 hours, then check the seals.
- Dial gauges: check yours every year and replace it if it is more than 2 pounds (about 14 kPa) out. Weighted gauges do not drift, which makes them easier to live with here.
Altitude: who in New Zealand needs more pressure
Most New Zealand towns sit low enough for the sea-level pressure. If you live inland on the Central Plateau (Taupō, Tūrangi, Ohakune, National Park) or in the Mackenzie Basin (Tekapo, Twizel), check your height above sea level first. Canner weights and dials read in pounds per square inch (psi); the metre bands below are rounded down from USDA's feet so you fall into the safer band.
| Height above sea level | Dial gauge | Weighted gauge |
|---|---|---|
| Up to 300 m | 11 psi (76 kPa) | 10 psi (69 kPa) |
| 301 to 600 m | 11 psi (76 kPa) | 15 psi (103 kPa) |
| 601 to 1,200 m | 12 psi (83 kPa) | 15 psi (103 kPa) |
That is the USDA setting for most vegetables, green beans included. Some foods use other pressures, so read the table for the food you are bottling. In a water bath, altitude adds time; in a pressure canner it adds pressure and the time stays the same.
Times for two common crops
USDA times are set for US pints (473 ml) and quarts (946 ml). A 500 ml jar is bigger than a pint, so it takes the quart time. Nothing has been tested in jars over a quart, so leave 1 litre jars for fruit.
- Green or runner beans, 2.5 cm headspace: 20 minutes for pints, 25 minutes for quarts.
- Pumpkin cubes (2.5 cm, boiled 2 minutes first): 55 minutes for pints, 90 minutes for quarts. Do not mash or puree pumpkin or kūmara for bottling; no tested time exists.
Checking and storing the jars
New Zealand Food Safety says throw away any preserved food that is badly damaged, bulging or looks spoiled. USDA adds: if the seal has failed, liquid spurts out, it smells off or there is mould, do not taste it. Put a sealed suspect jar in a strong rubbish bag and into the bin. Store good jars somewhere dark between 10 and 21°C, never above 35°C, and use them within a year.
If someone feels unwell after eating home-bottled food, call Healthline on 0800 611 116, or 111 if they have trouble breathing or swallowing.
See also: The four ways to preserve, Passata and bottling for the water bath method, and Pickling for the vinegar route.
Sources we checked (October 2026): New Zealand Food Safety (MPI), Clostridium botulinum or botulism: symptoms, causes and prevention; USDA Complete Guide to Home Canning (2015) through the National Center for Home Food Preservation: Using Pressure Canners, Equipment and Methods Not Recommended, Snap Beans, Pumpkins and Winter Squash, Storing Home Canned Foods; NCHFP, Can I Can in a Multi-Cooker?.
Common questions
Can I bottle beans with the overflow method?
No. The overflow method never heats the sealed jar, so botulism spores in beans survive and can grow. Beans need a pressure canner, the freezer, or a tested vinegar pickle.
Is overflow bottling safe for fruit?
It is traditional in New Zealand, but no agency has tested it, and USDA lists this open-kettle style of sealing as not recommended. A boiling water bath with a tested time is the safer way to bottle fruit.
Can I bottle kūmara or pumpkin?
Only as cubes in a pressure canner, following the USDA process. Mashed or pureed pumpkin and kūmara have no tested process and should be frozen instead.
Can I use my electric pressure cooker for bottling?
No. The National Center for Home Food Preservation says no tested process exists for canning in electric multicookers, even ones with a canning setting.
Who do I call about suspected botulism?
Call 111 if someone is struggling to breathe or swallow. Otherwise call Healthline on 0800 611 116 or see a doctor straight away.