Your WECK Jar Guide — Getting the Most from Every Jar

WECK jars have been made in Germany to the same principle since the early 1900s. The three-part seal; glass lid, natural rubber ring, stainless steel clips, is entirely reusable, contains no plastic, and gives a reliable, visible indication of whether the seal is intact. Here is everything you need to know.

The WECK Seal — How It Works

The rubber ring sits between the jar rim and the glass lid. When the clips are in place and the contents are sealed (either by heat processing or by refrigeration of fresh contents), a vacuum forms inside the jar and holds the lid down tightly. You can test whether the seal is intact at a glance:

  • Seal intact: the rubber tab points downward, pulled by the vacuum.

  • Seal lost: the tab springs upward or the lid moves freely. Refrigerate immediately and use soon.

How to Open a WECK Jar

Pull the rubber tab outward and upward. You will hear a hiss or a small pop as air enters the jar and releases the vacuum. Once you hear this, the lid lifts off easily. If you don't hear a hiss and the lid moves without resistance, the jar was not properly sealed. Check the contents before consuming.

 

Using WECK Jars for a Sourdough Starter

WECK jars are particularly well suited to sourdough starters. The wide-mouth opening makes adding flour and water and stirring straightforward. The glass lid with rubber ring allows gases to escape during active fermentation without letting contaminants in.  Place the lid on top without clips during peak activity. Once the starter is fed and resting in the fridge, fit the clips to seal fully. The rubber tab gives you an immediate visual check on fermentation activity. A rising tab can indicate pressure building inside.

Freezing

Most WECK jar shapes can be frozen, but not all. Cylindrical jars, cylinder glasses, gourmet glasses, and quad glasses are all suitable for freezing. Their straight sides allow ice to expand upward without cracking the glass. Avoid freezing jars with a bulbous or inward-tapering shape, as expanding ice can crack the glass from the inside. Leave a gap at the top of the jar. Do not fill to the brim before freezing.

You can freeze with the glass lid, rubber ring, and clips in place.


Baking in WECK Jars

Turning-out jars (mould-shape jars with a wider base than rim) are best suited for baking — the shape allows you to turn the baked item out cleanly. Square jars also work well for baked goods. For bread and cakes to release cleanly after baking, grease and flour the inside of the jar beforehand. Sponge cakes baked in WECK jars should not be greased — sponge batter needs the sides of the jar to climb during baking. Without greasing you can bake a light, airy sponge, but release will require more care.


What WECK Jars Are Made Of

WECK jars are made from soda-lime glass — approximately 70% quartz sand, 10% soda, 13% calcium carbonate (which improves temperature resistance), and 4% sodium sulphate (which prevents blistering during production). Modern production uses recycled glass as the main component. The rubber rings are made from natural rubber that remains stable down to -40°C.


Caring for Your WECK Jars

  • Jars and lids are dishwasher safe.

  • Rubber rings should be replaced periodically — inspect before each use for signs of cracking or deformation. Replacement rings, lids and clips are stocked at EcoBaker.

  • Stainless steel clips do not rust.

  • Store jars without clips attached to extend the life of both clips and rubber rings.