The simplest way to vacuum seal a mason jar
You can vacuum seal a mason jar using a standard countertop vacuum sealer and a jar attachment, or you can use the water displacement method with nothing but a pot of hot water. The attachment method is faster and works with any jar size; the water method costs nothing and works just as well for storage, though it takes longer and works best with smaller jars.
Both methods remove air and create a seal that keeps food fresh longer than an open jar. The seal is not as tight as commercial canning, but it stops oxidation and slows mold growth, which matters most for dry goods, nuts, coffee, and flour.
Key Takeaways
- A jar attachment for your vacuum sealer costs $15 to $30 and works with most standard countertop sealers and any mason jar size.
- The water displacement method requires only a pot of hot water and works without any equipment, though it takes 5 to 10 minutes per jar.
- The seal holds best on dry goods and foods with low moisture; wet foods can break the seal as they release liquid.
- Sealed jars stored in a cool, dark place keep dry goods fresh for months longer than unsealed jars.
Using a jar attachment with your vacuum sealer
A jar attachment is a small plastic or silicone accessory that fits over the sealing strip of your vacuum sealer. It has a tube that connects to the vacuum port on your sealer. When you set up the sealer, the tube draws air out of the jar instead of out of a bag.
To use one: place the attachment over the jar opening, press the vacuum button on your sealer, and hold it until the machine stops. The whole process takes 10 to 20 seconds. Most attachments work with quart and pint jars; some fit wide-mouth and regular-mouth lids. Check your sealer's manual to see if an attachment is sold separately or if one came with your machine.
The attachment method is reliable because the sealer does the work. The jar lid will dome slightly inward when the seal is complete. You can store the jar at room temperature, and the seal will hold as long as the lid stays clean and the jar is not bumped hard enough to crack it.
The water displacement method for sealing without equipment
Fill a pot with water and heat it until small bubbles form on the bottom (around 180°F, though exact temperature does not matter much). Place your mason jar on a stable surface with the lid sitting loose on top—not screwed down. Slowly lower the jar into the hot water until the water level reaches just below the lid rim. Hold it there for 30 seconds to 1 minute.
The heat forces air out of the jar and up through the gap between the jar and lid. As the jar cools, the air inside contracts, and the lid seals down. You will hear a pop or feel a click when the seal forms, usually within a few minutes of removing the jar from the water. Once it cools completely, screw the lid down tight.
This method works best with pint and quart jars filled with dry goods. Larger jars cool more slowly, and the seal may not form evenly. Jars filled with wet or oily foods are more likely to fail because moisture and oil can prevent a tight seal.
What foods and goods seal best in mason jars
Dry goods seal most reliably: flour, sugar, rice, pasta, beans, nuts, coffee, tea, and spices. These foods have no moisture to release, so the seal stays tight. Crackers, cereal, and dried fruit also work well.
Foods with moisture or oil—soups, sauces, jams, peanut butter, and honey—can break the seal as they release liquid or gas over time. If you seal these foods, check the jar every few days for the first week. If the lid pops back up, the seal failed and you should refrigerate the jar or use the food soon.
Do not seal raw meat, fish, or dairy products in mason jars without pressure canning. Vacuum sealing removes oxygen, which can allow dangerous bacteria to grow in low-oxygen environments. Sealed jars of these foods belong in the freezer, and you should use them within a few months.
How long sealed mason jars keep food fresh
A properly sealed jar of dry goods stored in a cool, dark cupboard will keep the food fresh for 6 to 12 months longer than an open jar. Flour and sugar last longest; nuts and coffee stay good for 6 to 9 months. Without a seal, these same foods begin to go stale or absorb moisture within weeks.
The seal works by stopping oxygen from reaching the food. Oxygen causes rancidity in nuts and oils, staleness in flour and crackers, and flavor loss in coffee. A sealed jar also keeps out insects and moisture, which is why sealed jars work well in humid kitchens or pantries.
Sealed jars in the freezer extend these timelines further. Frozen nuts, for example, stay fresh for a year or more. Check the seal every few months by pressing the lid center; it should not flex or pop. If it does, the seal has failed and you should use the food soon.
Troubleshooting a failed seal
If the lid does not dome inward or pops back up when you press it, the seal failed. Common causes are a dirty jar rim, a cracked or warped lid, or food particles stuck between the jar and lid. Wipe the rim clean with a dry cloth before sealing, and inspect the lid for cracks or dents.
With the water method, the jar may not cool enough to form a seal if the water was not hot enough or if you did not hold the jar in the water long enough. Try again with hotter water and a longer soak—up to 2 minutes for larger jars.
If you are using a jar attachment and the seal fails, check that the attachment is sitting flat on the jar opening and that the vacuum port is not clogged. Some sealers have a weak vacuum setting; switch to the strongest setting if your machine has one.
Comparing jar attachments and water displacement
| Method | Cost | Time per jar | Best for | Drawback |
|---|---|---|---|---|
| Jar attachment | $15–$30 one-time | 10–20 seconds | Any jar size, frequent sealing | Requires a vacuum sealer |
| Water displacement | $0 | 5–10 minutes | Pint and quart jars, occasional sealing | Slower, less reliable on large jars |
Frequently Asked Questions
Can I reuse mason jar lids after I vacuum seal them?
No. Once a lid is sealed, the rubber gasket is compressed and will not seal again. You must use a new lid each time. Jars and bands are reusable, but lids are single-use. This is true whether you use a jar attachment or the water method.
Will a vacuum-sealed jar work in the freezer?
Yes. Sealed jars freeze well and actually stay fresher longer in the freezer because cold slows all spoilage. Leave a little headspace (about half an inch) because food expands as it freezes and can crack the jar if it is completely full. Thaw sealed jars in the refrigerator, not on the counter.
What is the difference between vacuum sealing and pressure canning?
Vacuum sealing removes air and creates a tight seal, but it does not kill bacteria. Pressure canning heats food to a high temperature under pressure, which kills dangerous bacteria and makes the food shelf-stable for years. Vacuum sealing is for dry goods and foods you will use within months; pressure canning is for low-acid foods like vegetables and meat that you want to store at room temperature long-term.
Can I vacuum seal a jar that is already full of food?
Yes, if you use a jar attachment. The attachment draws air out of a full jar just as well as an empty one. With the water method, a full jar works too, but it cools more slowly and the seal may not form as reliably. Leave a little headspace (about an inch) to make sure the seal forms evenly.
Do I need to refrigerate a vacuum-sealed jar after I open it?
Once you open the jar, the seal is broken and air enters. Treat it like any open jar: dry goods can sit at room temperature, but foods with moisture or oil should go in the refrigerator if you do not use them right away.