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How to properly fill in, close and store Twist-off glass jars?

How to properly fill in, close and store Twist-off glass jars?
  • Quick reminder: pasteurization vs. sterilization / Filling and the notion of “headspace” / Manual closing: a few tips / Some storage recommendations


Quick reminder: pasteurization vs. sterilization

Both of these are processes for preserving food:

=> Pasteurization:

Objective: to destroy a portion of the germs present in the foodstuff and prevent the remaining germs developing

Procedure: the food is heated to a set temperature (between 62°C and 88 °C) over a predetermined time, followed by rapid cooling.

=> Sterilization:

Objective: to destroy all the germs in the foodstuff, microbial spores included

Procedure: the food is raised to a high temperature, which is always greater than 100°C (usually 120°C)

Focus on lids

Our lids come in 2 versions: one for pasteurisation and one for sterilisation

The difference between the two lies in the PVC gasket:

  • Pasteurisation lid: more supple
  • Sterilisation lid: firmer, softening up when heated

Safety button

N.B. The safety button does not tell you whether the lid is designed for pasteurisation or sterilisation: it is a SAFETY feature which indicates that a VACUUM seal has been formed before the pasteurisation or sterilisation process begins.

Containers are made airtight by the combination of two actions:

  • Screwing down
  • Vacuum sealing

The technical data sheet for the container as well as the lid should always be consulted in order to verify the processes and the maximum temperatures.

Filling and the notion of “headspace”

To avoid contamination of the lid by the contents, the container must not be overfilled.

Consider the example of a jar with a nominal capacity of 580ml (full-to-brim capacity)

=> For pasteurization, a headspace of roughly 5% is required; so the filling must not exceed 551ml, which is 5% below the nominal capacity

=> For sterilization, a headspace of roughly 9% is required; so the filling must not exceed 527ml, which is 9% below the nominal capacity

Manual closing of twist-off jars: a few tips

Glass packaging consists of two distinct items, a glass container and a metal lid. These 2 components are essential for an airtight package.

Although twist-off jars are nearly always closed by machine, closing by hand can also be effective.


=>  Heat the lid to soften the sealing ring very slightly, decreasing pressure on the lugs and creating a better seal.

But take care not to overheat! (maximum 60°C). This step is particularly advisable when cold filling.

=>  Fit the lid over the jar then give it a quarter turn clockwise: DO NOT OVERTIGHTEN or you could jump the threads and/or damage the seal!

How to check the lid is properly positioned?
We have placed marks the jar to illustrate the method as clearly as possible
This method is a good guide but should not be considered infallible

1- Use a lug on the lid and the two ends of a jar thread as your datum points

2- With the lid tightened and the jar on its side, look at the lug with respect to the thread - it must lie roughly 1/3 of the way along the thread going from right to left

If the lug is more than halfway along the thread, the lid is too tight! In this case the lug may have bent slightly, allowing the lid to move and risking a vacuum release. An overtightened lid must therefore be replaced with a new one.

If the lug does not reach a third of the way along the thread, the lid is too slack! This time the risk is that the lid will come off if the package receives a shock.

Some storage recommendations

  • When storing your jars, make sure the package (body and lid) is dry. If any moisture remains where the jar meets the lid, the lid can rust
  • Make sure the jars have cooled down before stacking and storing them.
  • To avoid condensation, store them in a dry, well-aired place not exposed to abrupt temperature changes.
  • Keep the jars away from corrosive substances