A smell proof jar has two jobs. Keep air out. Keep smell in. Both jobs belong to the seal, not to the lid, the glass or the price.
Most jars only do the first. A clip lid with a thin rubber ring stops air rushing in, and it still lets the smell of ground coffee drift across a cupboard. A smell proof jar needs a seal that stays tight under pressure, every time you close it.
Here is what separates the two, a test you can run tonight, and how to choose between glass, steel and size.
Airtight is not the same as smell proof
Airtight means air does not get in. Your biscuits stay crisp.
Smell proof means smell does not get out either. Open the cupboard and you smell the cupboard, not the coffee in it.
A jar can pass the first and fail the second. Smell is made of molecules small enough to find the gap a rubber ring leaves after months of opening and closing. The tighter and thicker the seal, the less there is to find.
What actually seals: four kinds of lid
| Lid | How it closes | Airtight | Smell proof | Weak point |
|---|---|---|---|---|
| Screw lid, no seal | Thread on thread | Partly | No | The thread is not a seal |
| Clip lid, thin rubber ring | Lever presses ring | Yes, when new | Partly | The ring flattens and hardens |
| Thick silicone O-ring | Ring compressed in a groove | Yes | Yes, when seated | A ring that is dirty or out of its groove |
| Vacuum lid with O-ring | Air pumped out, ring pulled tight | Yes | Yes | Needs charging |
The pattern: the more the seal is pressed, the better it holds. A vacuum does the pressing for you. Pull the air out of the jar and the outside air pushes the lid down onto the ring.
The smell proof jar test you can run tonight
You do not need to trust a label. Use ground coffee. It is strong, cheap, and everyone knows the smell.
- Put two tablespoons of freshly ground coffee in the jar and close it the way you normally would.
- Wipe the outside of the jar with a damp cloth, then dry it. Coffee dust on the glass will fool you.
- Put the jar in a small cupboard or a drawer that has nothing else smelly in it. Close it.
- Leave it overnight.
- In the morning, open the cupboard and smell before you touch the jar.
If you smell coffee, the jar leaks smell. Check the seal first: most leaks start with a ring that is dirty, twisted or worn flat.
Run the same test after a month of daily use. A jar that passes new and fails at four weeks has a seal that is giving up.
Glass or stainless steel
Glass shows you what is inside and how much is left. It does not take on smells from what you stored last, and it goes in the dishwasher. It breaks if you drop it.
Stainless steel lets in no light at all and survives a bag. Light fades colour and aroma just as air does, so a jar on an open shelf in the sun loses more than one in a dark cupboard.
Pick glass for the kitchen counter and the cupboard. Pick steel for a sunny shelf, for travel, or for anything sensitive to light.
How Terp Seals jars seal
Terp Seals is the maker we stock, because its jars do the pressing for you.
- A vacuum pump in the lid. Close the jar, switch the vacuum on, and the lid pulls the air out. Terp Seals says the system constantly monitors the inside and automatically blocks air and pressure leaks. If pressure creeps back in, the lid pumps again.
- A thick silicone O-ring. Terp Seals calls it a "3X" O-ring, three layers thick.
- A display on the lid. Humidity, temperature and how many days the jar has been closed. Useful for coffee and tea, where the age of the batch matters.
- USB-C charging. The lid runs the pump and the display, so it needs charging.
- Vacuum on or off. Switch it off and you have a plain airtight jar with a very good seal.
Which Terp Seals jar
| Jar | Body | Capacity | Pick it for |
|---|---|---|---|
| Terp Seals glass jar | Glass | Everyday size | Seeing what is inside |
| Terp Seals Inox | Stainless steel | 500 ml | No light, travel |
| Terp Seals XL | Square, large | Largest in the range | Buying in bulk |
Want two things in one jar? The Smart Seals divider drops in, locks with a turn and splits one jar into labelled sections under one vacuum lid. Despite the name, it is a divider, not a seal. The rubber seal is a separate spare part.
See the full range, cover included, on the storage shelf.
What to keep in a smell proof jar
Anything that loses its smell to air, or gives its smell to the cupboard.
- Coffee beans and ground coffee. The smell is the flavour. Air takes both.
- Loose tea. Especially smoky or floral teas that perfume everything near them.
- Spices. Whole cumin, cardamom, cloves, smoked paprika.
- Dried herbs. Rosemary, thyme, oregano for herb oils and butters.
How to keep the seal working
A seal is the part that wears. Look after it and the jar lasts.
Keep the ring clean. Coffee dust or spice powder on the O-ring makes a gap. Wipe the ring and the rim each time you refill.
Seat it properly. After washing, press the ring evenly back into its groove all the way round. A twisted ring leaks.
Dry everything fully. Water trapped under the ring stays there once the lid is closed.
Never put the lid under water. The Terp Seals lid holds the pump, the display and the battery. Wash the glass or steel body; wipe the lid.
Replace a worn ring. A ring that has gone flat or cracked is the usual reason a good jar starts to leak. Terp Seals sells the seal as a spare part.
Spare parts and the cover
Jars last. Parts wear. Buying the part is cheaper than buying the jar again.
- The seal. Terp Seals sells it as a spare. Replace it when it has gone flat or cracked.
- The XL valve. Sold as a spare for the XL jar.
- The jar cover. A sleeve that takes the scuffs and knocks in a bag, so the jar does not. It does not touch the seal; the lid and the O-ring still do the sealing.
If your jar travels, the cover is worth adding. If it lives in one cupboard, a spare seal in the drawer is the better buy.
FAQ
Is an airtight jar the same as a smell proof jar?
Not always. Airtight means air cannot get in. Smell proof also means smell cannot get out. That takes a seal tight enough to hold under pressure. A vacuum seal does both.
How can I test if a jar is smell proof?
Close two tablespoons of ground coffee in it, wipe the outside, and leave it in a closed cupboard overnight. If the cupboard smells of coffee in the morning, the jar leaks.
Glass or stainless steel?
Glass to see inside. Stainless steel to keep light out and to carry it.
Does a Terp Seals jar need charging?
The lid does, over USB-C. It runs the vacuum and the display.
Why has my jar started to smell?
Check the seal. A dirty, twisted or flattened O-ring is the usual cause. Clean it, seat it, and replace it if it has gone flat.
