The Two Methods for Vacuum Sealing Canning Jars
You can vacuum seal canning jars using either a vacuum sealer machine with a special jar attachment, or the water displacement method (also called the boiling water method). The machine method is faster and more reliable if you own a food vacuum sealer already. The water displacement method requires only a pot of boiling water and works with any jar, but takes longer and leaves more air in the jar than a machine does.
Both methods work best with wide-mouth canning jars because the opening is larger and easier to work with. Standard-mouth jars can be sealed either way, but you will need a narrower attachment or more careful technique. The seal you create is not the same as pressure canning — it is a storage seal that keeps air out and extends shelf life, but does not preserve foods that require heat processing for safety.
Key Takeaways
- A vacuum sealer with a jar attachment pulls air directly from the jar and seals it in seconds, and works best with wide-mouth jars.
- The water displacement method uses boiling water to push air out of the jar as you lower it into the pot, and requires no special equipment.
- Vacuum-sealed jars keep dry goods, nuts, and pre-cooked foods fresher longer, but are not a substitute for pressure canning when safety is required.
- After sealing, store jars in a cool, dark place away from direct sunlight to prevent the seal from weakening.
Using a Vacuum Sealer Machine with a Jar Attachment
If you own a food vacuum sealer, check whether it came with a jar attachment or whether one is sold separately for your model. The attachment is a small tube or hose that connects to the sealer's vacuum port and fits into the mouth of the jar. Place the jar on a flat surface, insert the attachment into the jar opening, and press the vacuum button. The machine will pull air from the jar for a few seconds, then seal the opening with a strip of plastic or a rubber gasket, depending on your sealer model.
The entire process takes 10 to 20 seconds per jar. You do not need to heat the jar or the food inside. This method works well for dry goods like flour, sugar, coffee, nuts, and crackers, as well as for pre-cooked meals you want to store in the refrigerator or freezer. The seal is tight enough to keep moisture and air out, which slows spoilage and extends freshness.
Check your sealer's manual to confirm the jar size it accepts — most attachments work with quart and pint jars, but not all work with half-pint or gallon sizes. If your sealer did not come with an attachment, you can often buy one from the manufacturer or from retailers that sell vacuum sealer accessories, though the cost varies by brand and model.
The Water Displacement Method for Sealing Jars
The water displacement method requires a large pot, boiling water, and a jar lifter or tongs. Fill the pot with water and bring it to a rolling boil. Place your filled jar on the counter and position a clean, dry canning lid on top of the jar opening — do not screw the band down yet. Slowly lower the jar into the boiling water, keeping it upright, until the water level reaches the shoulder of the jar (the point where the sides start to narrow toward the neck).
Hold the jar in the boiling water for 10 to 15 seconds. The heat and steam will push air out of the jar and create a partial vacuum as the jar cools. Carefully lift the jar out of the water using a jar lifter, and place it on a towel to cool. Once the jar has cooled completely — usually 12 to 24 hours — you can screw the band down tightly. The lid will have sealed to the jar rim, and you will hear a faint pop or feel a slight give when you press the center of the lid.
This method works with any canning jar and requires no equipment beyond what most kitchens already have. It is slower than using a machine and leaves slightly more air in the jar, but it is reliable and costs nothing. It works best for dry goods and foods that do not require heat processing for safety.
What You Can and Cannot Seal This Way
Vacuum sealing jars works well for dry goods like flour, sugar, rice, pasta, cereal, nuts, and spices. It also works for pre-cooked foods you plan to refrigerate or freeze, such as leftover soups, stews, or cooked grains. The seal keeps air and moisture out, which slows the growth of mold and bacteria in the refrigerator and prevents freezer burn in the freezer.
Vacuum sealing does not replace pressure canning for foods that need heat processing to be safe. Low-acid foods like vegetables, meats, and fish require pressure canning at a specific temperature and time to kill harmful bacteria. Boiling water canning (used for jams and pickles) is different from vacuum sealing. If you are preserving foods for shelf-stable storage without refrigeration, follow USDA canning guidelines rather than relying on vacuum sealing alone.
How to Check the Seal and Store Sealed Jars
After the jar has cooled, press the center of the lid with your finger. A good seal will feel solid and slightly concave (pushed inward). If the lid flexes up and down or pops when you press it, the seal did not hold. Jars with failed seals should be opened, the food transferred to a new jar with a fresh lid, and the sealing process repeated.
Store sealed jars in a cool, dark place such as a pantry, basement, or cabinet. Keep them away from direct sunlight, heat sources, and temperature swings. Jars stored in a stable environment will hold their seal longer than those exposed to light or heat. Check the seal occasionally by pressing the lid — if it starts to flex again, the seal is weakening and the food should be used soon or transferred to a new sealed jar.
Comparing Machine Sealing and Water Displacement
The choice between methods depends on what equipment you already own and how many jars you plan to seal. If you use a vacuum sealer regularly for bags and pouches, adding a jar attachment is a quick way to seal containers without extra steps. If you do not own a sealer, the water displacement method costs nothing and produces a reliable seal with tools you likely have in your kitchen.
Machine sealing is faster when you have many jars to process, since each jar takes only 10 to 20 seconds. Water displacement requires cooling time between batches, so sealing 20 jars can take several hours from start to finish. For occasional use or small batches, the water displacement method is practical and straightforward. For regular, high-volume sealing, a machine with a jar attachment saves time.
| Method | Time per Jar | Equipment Needed | Best For | Cost |
|---|---|---|---|---|
| Vacuum sealer with jar attachment | 10–20 seconds | Vacuum sealer, jar attachment | Dry goods, pre-cooked foods | Attachment cost varies by brand |
| Water displacement method | 10–15 seconds in water, plus cooling time | Pot, boiling water, jar lifter or tongs | Dry goods, pre-cooked foods | No additional cost |
Frequently Asked Questions
Can I vacuum seal a jar that already has food in it?
Yes. Fill the jar with the food you want to store, leaving about half an inch of space at the top. Wipe the rim clean and dry before sealing. If you are using the water displacement method, make sure the food is not so full that water will enter the jar when you lower it into the pot.
How long do vacuum-sealed jars stay fresh?
Shelf life depends on what is inside and how it is stored. Dry goods like flour and sugar can last one to two years in a vacuum-sealed jar kept in a cool, dark place. Pre-cooked foods in the refrigerator usually last three to five days. Frozen pre-cooked foods can last several months. Check the food for signs of spoilage before eating.
Do I need special lids for vacuum sealing?
For the water displacement method, use standard two-piece canning lids (the flat lid and the screw band). For a vacuum sealer machine, check your sealer's manual — some use the same standard lids, while others use reusable rubber gasket lids designed for that specific sealer model.
Can I reuse the lids after opening a vacuum-sealed jar?
Standard canning lids are designed for one-time use and should not be reused for sealing. If your vacuum sealer uses reusable rubber gasket lids, you can reuse them multiple times as long as they are not damaged. Wash them by hand and inspect them for cracks or warping before each use.
What if the jar cracks when I put it in boiling water?
Thermal shock — the sudden temperature change — can crack glass. To prevent this, let the jar come to room temperature before placing it in boiling water, or use a jar that has been warmed gradually. If a jar cracks, discard it and use a new one. Never use a cracked jar for food storage.