User FAQ
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User FAQ

In the following, you will find often asked user questions and the accordingly answers about advices and tips. The content is based on the category „preserving service“ of the „WECK Landjournal“ magazine.


If you have any questions or helpful tips, don´t hesitate and write us. Please use our contact form to do so.

Preserve desserts


„The Crème Brûlée from the September/October-issue 2014 tastes great. I'd like to serve it next time at a party, but want to prepare it in advance and therefor preserve it. Is this possible?“

Sylvia F., via E-Mail


We are sad to tell you, that it's not possible to preserve the Crème Brûlée. The preserving-jar was just used for portioning, but it makes it also comfortable to store in fridge. You can prepare it 2 - 3 days in advance and store it in the fridge, closed using rubber rings, glass-lids and clamps.

Generally it's not that easy to preserve desserts, but you can preserve semi-finished products, like e.g. a cake, which you can cut off a day before the party an decorate it with cream and fruits in the jars.

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White film in jar


„I have preserved plums and I probably filled the jars too full, so that a bit of liquids had entered outwards, but the other jars are fine. Now, I can see at the inside of the glass lid (oft he too full filled ones) a slight white film. I´m not sure, if this is mouldiness or something else, but I don´t want to throw away the whole charge. How can I be sure, whether the plums are still alright? My first thought war, to leave the jars standing and to wait, if the jars open, because of the fermentation gas. Is this a safe method?

Johannes A., via E-Mail


Mouldiness on surfaces have a lot of reasons. Mostly, it depends on the temperature, so maybe your content was not heated enough. With fruits, 30 minutes preserving of 90 degrees of hot water is a minimum to kill fungal spores. There are more than thousands of kinds of mouldiness spores, plus in different colours. There is often watched a slightly white film. Contrary on the assumption, mouldiness doesn´t form fermentation gas unlike a lot of other bacteria.

In your case, the vacuum of the jars is stable and the jars are still closed. Stone fruits have a waxy surface. The wax is melting during heating, so it´s clinging in a white-greyish sort of film to the glass surface. Without being able to look at your jars right now, we can´t judge the problem. Which means, we can´t tell you, if the white film is mouldiness or a segregation from the fruits. We advise you at first, to keep an eye on the jars. The waxy segregations are not changing anymore, but the mouldy places can spread. If this is the case, we urgently recommend you to throw away the content of the infested jars, to wash them out very thoroughly and to replace the rubber rings.

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Jars are swimming or are instable


„It often happens that my jars are swimming or are standing very insecure inside my cooking pot. Is there any chance to stabilize the jars“?

Peter A., via E-Mail

This phenomenon often occurs, especially when you are preserving cakes. Absolutely avoid the rising of the jars inside your cooking pot. Because of the rubbing against each other, the jars get tiny scratches, which can lead to glass breaking. Try to weight down the jars, so they can stand safely. The easiest way to do so: Fill empty jars with water and place them on top of the other jars. This weight should be enough to stop the rising.

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Microwaving preserved?


„I'd like to microwave preserved food or half-baked cake in a jar. Is that possible?“

Yukiko S., via E-Mail

Preserving-jars are ideal for microwaving, if you are heating from room temperature. That means: Jars out of the fridge or the freezer should not be heated directly - that would cause a thermal shock - they must be heated slowly until they got room temperature. This also applies before putting them into the preheated oven or by taking them out of the pot and placing it on a cold underground.

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Insect protection


„After a pest infestation in our kitchen we are searching for a storage possibility for grain, rice, flour etc. We got the idea of using Weck-jars, because they are contaminant-free, but it seems to be impractically to always use the clamps. Is it possible to only use the Weck plastic-lid, or is it not tight enough, so that moths or other insects can get in?“

Miriam N., via E-Mai


Our preserving-jars are tight even by using the plastic-lid, but you shouldn't use one lid for different contains, because it may adopt the smell, e.g. by spicery. The plastic lid is safe as long as it doesn't deform by heat or wrong storage. The preserving-jar is harmless to the health, and the weight of the glass-lid is effectual for closing and don't necessarily needs clamps, and the air exchange is guaranteed. By using the rubber ring and the clamps, an air exchange is impossible.

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Heating-up time of the preserving pot


„It nearly takes 30 minutes until the warning light lapses if the preserving pot is half filled. Is that ok? I don't want to preserve the food to long.“

Christa S., via E-Mail


A long heating-up time is unavoidable, because with a small real power a large volume must be heated up. The cause for this defined small real power is that the temperature of the jars content needs more time for heating-up than the surrounding water. If the water heats up to fast, the warning light would signalise, that the preserving process already began, even if the required temperature in the jars is not yet achieved. The consequences are that the jars won't close and the content perish. In addition the food may stick under the lid and the creation of vacuum in the jar is at risk. Please hold on to the proofed times and temperatures for preserving. The sum of heating-up time and cooking time makes the success.

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Rubber pull demolished


„It often happens to me, that while opening a perfect preserved jar, the rubber pull demolished. I quit trying to open it with screwdrivers or other instruments, because rather the jar brakes than I get the content. Did you have a tip?“

Peter B., via E-Mail

You did right to pass on using screwdrivers and knifes, precisely because there is a high risk of injury. If a jar wont open, the first try would be to put the clamps on the lid, put the jar upside down in a pot of water and heating it up. The content will enlarge, presses on the lid from the inside and the vacuum passes off. If you now take the jar out of the pot and remove the clamps, the jar will be open. Another method: retailers offers special jar openers: a wire snare has to be put between jar and lid and tightened with a clamping lever, the vacuum passes off. 

The demolishen of rubber pulls are often linked to preserving in the oven: the dry heat makes the rubber rings rubish and fragile.


The opening should happen in the same angle as the pull points; at older jars upwards, at round rim jars downwards. If you pull the rubber horizontal, it passes a sharp glass edge with the danger of tearing.

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Apples rising in jar


„I preserved apples, therefore I used round rim jars fully filled with a sugar mixture. After preserving, one part was ok, but at the others nearly one third of the liquid went out of the jar and the apples are now swimming at the top of the jar and are no longer covered by the sugar mixture. The jars are completely closed. What did I do wrong? And do the apples remains intact anyway?

Ruth B., via E-Mail


Apples, like much other fruits, generate at a specific degree of ripeness an upswing while heating up and my push besides air also liquid out of the jar. During the cooling-off period the content pucker up with the result you describe. There is no derogation of the storage life. To work against this problem, you should slowly heaten-up the water while preserving. Another reason may be, that there is too much food in the jar. Plenum chambers may arise, which can't be filled by sugar- or vinegar-mixtures. In this case, stack your food more loose.

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Half filled jars


„I ran out of small jars, but want to preserve only a small quantity. Is it possible to use large jars and just fill them half of the top?“

Marga R., via E-Mail


Even if the jars are only filled moderate, there will cause a vacuum while heating-up. But because of the oxygen left in the jar, oxidation will began, which may change the colour of the food within the jar and nutrients may get lost. Some may remember this process of former times, as at the "old" solid rim jars oxygen was left under the lid. The upper layer of e.g. pears, apples or applesauce changed their colour to brown. Advised by nutritionists, the new round rim jars are configured for optimal - up to the rim - filling, so that all air passes off and a vacuum occurred. So the upper layer within the jar no longer changes its colour. 

Pasty food like applesauce, greasy sausages and meat dishes need some space for expansion; spare 2 - 3 cm below the rim. In exceptional cases it is possible to half fill large jars, but for best results we recommend to adapt the size of the jar to the quantity you want to preserve.

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Jars burst


„Yesterday I used my Weck jars for baking again. I made a cherry-crumble which had to be baken at 200° C in the oven. After I took the jars out of the oven and covered the cherry-crumble with vanilla-sauce, I could watch the jars bursting. How does that happend?

Nadine G., via E-Mail


Preserving jars are not "fire-proofed", although they can be heated-up to more than 100° C. Their melting-point is about 830° C! But what they don't like are thermal shocks, then they burst. Preserving jars have a thermal-shock-tolerance from about 50 to 60° C. That means, that you have to put the jars after you took them out of the oven on proper underlay (e.g. a folded towel) for cooling, before you serve it with a coolish or cold vanilla-sauce.

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Baking in closed jar


„I read that it's possible to bake cakes in closed jars. Is that really possible?  I don't dare to try it.“

Dorothea D., via E-Mail

We advise to bake in open jars to get the best result. But baking in closed jars is possible, although there are some negative points:

  • While the jar is closed, you can't proof the temperature and must depend on the cooking time which is written in the recipe. We strongly advice to make the proof, if the cake is well baked, otherwise the storage life is not guaranteed.
  • If you bake in closed jars, you have to take exactly the right portion of dough, while by baking in open jars the amount can be readjust by cutting the dough down to the top of the jar before preserving.
  • The rubber ring may get harmed due to the high temperatures in the oven, what means that it can get prudish or gluey. If you choose to bake in closed jars, we therefore recommend you to use a new rubber ring each time.


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Here you can read more worth knowing, e.g. how glass is produced.

Glass production