The basic method: using a FoodSaver or similar sealer

You can vacuum seal a mason jar using a countertop vacuum sealer and a special jar attachment, or by using the water displacement method with no equipment at all. The easiest route is a jar sealing attachment — a small plastic tube that fits over the vacuum sealer's nozzle and screws onto the mouth of a mason jar. You place the attachment on the jar, press the vacuum button, and the sealer removes air through the tube while you hold it steady. When the jar reaches the right pressure, the sealer stops automatically and you unscrew the attachment.

Most FoodSaver models and similar brands sell jar attachments separately for $15 to $25. They work with standard mason jar mouth sizes — typically regular (1.75 inches) or wide (2.25 inches) — so check which size your jars are before buying. The attachment is reusable and lasts for years if you keep it clean and dry between uses.

If you do not own a vacuum sealer, the water displacement method costs nothing and works just as well for dry goods. You fill the jar, leave about an inch of headspace, seal it loosely with the lid, then slowly lower the sealed jar into a pot of boiling water until water reaches the jar's shoulders. The heat and water pressure force air out of the jar. When you lift the jar out and let it cool, the lid seals itself as the air inside contracts. This method takes longer but produces the same airtight seal.

Key Takeaways

  • A jar attachment for your vacuum sealer costs $15 to $25 and screws onto the jar mouth while the sealer removes air through a tube.
  • The water displacement method requires no equipment — you lower a loosely sealed jar into boiling water until the lid seals itself as it cools.
  • Vacuum-sealed mason jars keep dry goods like flour, sugar, and coffee fresh for months longer than unsealed storage.
  • Check your jar mouth size (regular or wide) before buying an attachment, since they are not interchangeable.
  • Both methods work best with dry goods; liquids and wet foods can clog the sealer or prevent a proper seal.

What works best in vacuum-sealed jars

Dry goods seal most reliably and stay fresh longest in vacuum-sealed mason jars. Flour, sugar, rice, pasta, cereal, nuts, coffee beans, and dried herbs all benefit from the airtight environment. These items typically last two to three times longer in a sealed jar than in their original packaging or a regular container, because oxygen and moisture cannot reach them.

Avoid sealing anything wet or oily — soups, sauces, peanut butter, honey, or oil-packed items. Liquids can be drawn into the vacuum sealer and damage it, and oils can prevent the lid from sealing properly. Soft breads and baked goods can also crush under the vacuum pressure, so reserve those for regular storage.

Step-by-step with a jar attachment

Start with a clean, dry jar and lid. Fill the jar with your dry goods, leaving about an inch of headspace at the top — this space is where the air gets pulled out, and without it the seal will not form correctly. Screw the lid on by hand until it is snug but not tight; you want it loose enough that air can escape during the vacuum process.

Attach the correct size tube to your vacuum sealer's nozzle. Screw the tube onto the jar's mouth firmly so it does not slip during sealing. Press the vacuum button on your sealer and hold the tube steady. You will hear the air being pulled out and feel the jar getting slightly softer as pressure drops inside. Most sealers stop automatically when they reach the right vacuum level — usually after 10 to 20 seconds.

Once the sealer stops, unscrew the tube from the jar. The lid should now be pulled down tight against the jar, and you should hear a slight pop or feel resistance when you try to open it. If the lid is still loose, the seal did not take — this usually means the jar was not clean, the lid was damaged, or the headspace was too small. Wipe the jar rim with a dry cloth and try again with a fresh lid.

The water displacement method without equipment

Fill your mason jar with dry goods and leave an inch of headspace. Place the lid on the jar and screw the band on loosely — tight enough to stay in place but loose enough that steam and air can escape. Bring a pot of water to a rolling boil and carefully lower the jar into the water until the water level reaches the jar's shoulders. The heat will force air out of the jar and create steam inside.

Leave the jar in the boiling water for 10 to 15 minutes, depending on the jar size. Larger jars need more time. Carefully remove the jar with tongs and set it on a clean towel to cool. As the jar cools, the air inside contracts and the lid gets pulled down tight. You will hear a distinct popping sound when the seal forms — this is the lid snapping down. Once the jar is completely cool, check the seal by pressing the center of the lid. It should not flex or move.

If the lid did not seal, the jar was probably too warm when you removed it or the seal surface was wet. Let the jar cool completely, dry the rim, and try the process again with a fresh lid.

Storage and shelf life after sealing

Store vacuum-sealed mason jars in a cool, dark, dry place — a pantry or cupboard works well. Keep them away from direct sunlight and heat sources like stoves or radiators, because light and warmth can degrade the contents even in a sealed jar. A basement or closet is ideal if you have one.

Properly sealed jars will keep dry goods fresh for six months to a year or longer, depending on what you are storing. Flour and sugar last the longest. Coffee beans stay fresh for several months. Nuts and seeds, which contain oils, last three to six months. Once you open a sealed jar, treat it like any other container — the contents will start to lose freshness within a few weeks.

Check your sealed jars occasionally for signs of damage. If you notice the lid has popped back up, the seal has failed and the contents are no longer protected. Discard the food or transfer it to a new sealed jar.

Choosing between a sealer attachment and water displacement

Use a jar attachment if you seal jars regularly and already own a vacuum sealer. The process is fast, consistent, and requires almost no skill once you get the hang of it. The attachment is a one-time purchase that pays for itself after a few uses.

Use the water displacement method if you seal jars only occasionally, do not own a sealer, or want to avoid buying extra equipment. It works just as well and costs nothing. The trade-off is time — the process takes 20 to 30 minutes from start to finish, including cooling time. It also requires careful handling of boiling water, so it is not ideal if you have young children in the house.

Some people use both methods depending on what they are sealing. A sealer attachment is faster for large batches, while water displacement is better for single jars or when you want to avoid any risk of liquid damage to your equipment.

Common mistakes and how to avoid them

The most common reason a seal fails is too much headspace or not enough. Leave exactly one inch at the top — no more, no less. Too much space means the sealer cannot pull enough air out to form a tight seal. Too little space means the lid cannot be pulled down far enough to create the seal line.

Another frequent problem is a dirty or wet jar rim. Even a tiny speck of food or a drop of water will break the seal. Wipe the rim thoroughly with a clean, dry cloth before sealing, and make sure the lid and band are also dry.

If you are using a sealer attachment, do not hold the tube at an angle or let it slip during the vacuum process. Keep it straight and steady, and do not remove it until the sealer has finished and stopped on its own. Pulling it away too early will let air back into the jar.

With the water displacement method, do not let the water level go above the jar's shoulders — this can force water into the jar and ruin the contents. Also, do not skip the cooling step. The jar must cool completely before you check the seal, or you will get a false reading.

Frequently Asked Questions

Can I reuse mason jar lids after vacuum sealing?

No. Once a lid has been vacuum sealed, the seal surface is damaged and cannot seal again. You must use a fresh lid each time you seal a jar. Bands and jars themselves are reusable indefinitely, but lids are single-use.

Will vacuum sealing mason jars prevent mold or insects?

Yes. An airtight seal keeps out insects, dust, and moisture — all of which can cause mold or spoilage. Vacuum-sealed jars are much more resistant to contamination than open storage, which is why they are popular for long-term dry goods storage.

What size jar attachment do I need?

Mason jars come in two standard mouth sizes: regular (1.75 inches) and wide (2.25 inches). Check your jar by looking at the lid or measuring the opening. Buy the attachment that matches your jar size. Some sealer brands sell universal attachments that fit both sizes, but they are less common and more expensive.

Can I vacuum seal jars with a handheld vacuum sealer?

Handheld sealers are designed for bags, not jars, and do not work with jar attachments. You need a countertop model with a flat sealing surface and a nozzle port. If you only have a handheld sealer, the water displacement method is your best option.

How do I know if the seal worked?

Press the center of the lid with your finger. It should not flex or move — it should feel hard and fixed in place. You may also hear a slight pop when you first press it, which is the seal breaking slightly and then re-forming. If the lid moves easily or pops back up, the seal failed and you should try again with a fresh lid.