4. Rigid Materials

4.2. Lids

Glass bottles and jars need to be sealed with a lid. Depending on the product and the bottle or jar type, different alternatives are available:

1. Twist-off and continous thread (CT) lids

Twist-off and CT lids are ideal for closing jars. Both are suitable for hot-filling. However, for products that need sterilization by water bathing or otherwise a high-heat lid, a continuous thread lid is the better option.


2. Special lids for oily foods (e.g. blue seal, thermoplastic elastomere)

The sealing material on the inside of conventional twist-off lids is not oil-proof, as it can dissolve when in contact with oil. For oil or oil containing foods, loke dressings, marination, chutney, etc. it is necessary to use special, oil-proof lids as described below:

used for:

type E

Cold filling, without further treatment

type T

Cold or hot filling, pasteurization at max: 95◦C for 1hour, without pressure, minimum 5-7% headspace

type K

Hot filling, sterilization at max: 121◦C for 1hour, 2,5 bar pressure, min. vaccum -0,35 bar, max. pressure difference: 1 bar, minimum 7-9% headspace

 

3. Aluminium screw caps:

Aluminium screw caps come in many versions, some are for manual bottle sealing, while the roll-on cap is for machine-sealing of bottles. Some come with sleeves (for wine), twist-off rings for product safety, or even pourers for flow-control (e.g. used in oil bottles).


Automated capping with screwcaps                                   Manual screwcap sealer

Image source: https://www.lodhapharma.com/cap-sealing-machine.php                Image source: https://www.tenco.it/en/manual-cap-sealing-tool-bottles        

For hotfilling of fruit or vegetable juices, these caps can come with a ventilation system (see gif of VACU VENT below), which releases gas or hot air under pressure and produces a vaccum seal when cooling down.


VACU VENT source: http://www.mw-wipperfuerth.de

4. Bottle caps (crown cork)

The bottle cap is a single-use lid, usually used for beer or sodas, which are sold in bottles smaller than 1 liter. A bottle opener is needed to remove the cap. They can be used industrially but also in small, ma´nual production.

 


5. Clip-on or swingtops and rubber seals

Jars used for preserving fruits and vegetables through pasteurization or sterilization are usually covered with a fitting glass lid and a rubber seal. To keep both in place during the pasteurization or sterilization process they are clipped on with either single clips or swingtop clips. Swingtop lids are also sometimes used for beer bottles. To ensure a tight sealing between jar and lid it is crucial to ensure both the seal and the rim are compelete clean when closing the jar. 

 

jar, lid, seal and clips                                   closed jar                         jar with swinglid         bottle with swinglid