Why Do Jar Lids Bulge After Autoclaving and How to Prevent It?

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Why Do Lids Bulge?

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Why Do Jar Lids Bulge After Autoclaving?

Preparing homemade preserves in jars using an autoclave is a reliable method of preserving food, ensuring long-term storage. However, even when following all instructions, we can end up with the unpleasant sight of bulging lids on jars. This situation raises doubts about the quality and safety of the preserved products. In this article, we will discuss the main reasons why lids bulge during autoclaving and share practical and effective tips on how to avoid this.

Types of Bulging Lids

Bulging lids immediately after autoclaving
Bulging lids during storage

It is important to distinguish between these two cases, as the reasons for the problem differ, and thus the solutions are also different.

Type One: Bulging Lids Immediately After Autoclaving

Most often, this is not critical, and this situation is merely a visual problem with the lid. Place such jars in the refrigerator or another cool place – there is a high likelihood that the lids will retract. The product in such jars is usually safe to consume.

Type One. Cause 1 - Temperature of Water and Products.

One of the most common causes of bulging lids is a temperature difference. It is important that the water you pour into the autoclave is at room temperature. If it is too cold, it can cause a sharp cooling, leading to bulging lids. The same applies to the products placed in the jars – they should also be at room temperature. If the products are too cold, you will get bulging lids after autoclaving.

Type One. Cause 2 - Non-Hermetic Autoclave.

If your device has lost its hermeticity and started to leak air, the pressure inside will be unstable, which may cause bulging lids. Ensure that after complete cooling, the autoclave maintains exactly 1 atm; if this is not the case, and you cannot resolve the reason for the dehermetization yourself, contact us for autoclave diagnostics.

Type One. Cause 3 - Overfilled Jars.

During sterilization and preparation, the product expands, and there must be enough free space in the jar for air circulation. Improper filling of the jars causes bulging lids; to avoid this, jars should not be filled to the very top, leave a 2 cm air gap to the edge of the jar.

Type One. Cause 4 - Improper Air Release.

Rapid or premature air release from the autoclave can also result in damaged lids, so air should only be released after the temperature inside the autoclave has dropped to 30°C when autoclaving with SКО lids, and to 60°C - 70°C when preserving with twist-off lids or retort pouches, and it should be done gradually.

Type One. Cause 5 - Low-Quality Lids.

Autoclaves and poor-quality lids for preservation do not go together! Lids made from thin steel are not designed for pressure fluctuations and are unsuitable for sterilization at high temperatures in an autoclave. We recommend using specialized lids that have a reinforced wall and are designed for autoclaving. The quality of the lids plays a crucial role in the autoclaving process. For preservation with SКО lids, use special clamps on the jars, which are available for order on the site.

Type Two: Bulging Lids During Storage

This is a sign that the product is spoiled. Such preserves must be disposed of immediately, as consuming such products is dangerous and may cause health issues.

Type Two: Cause 1 - Poor Quality Products.

If the product was spoiled before autoclaving, sterilization will not save the situation. Over time, such products continue to spoil, leading to bulging lids during storage.

Second Type: Reason 2 - Inadequate Autoclaving.

If the recommended autoclaving regimes are violated or not followed, the product remains unsterile. Pathogenic microorganisms begin to develop inside the jar, which leads to bulging lids some time after canning.

Avoid Autoclaving Problems by Following Our Tips!

Carefully follow the autoclaving instructions, including temperature regimes, sterilization times, and storage rules for finished preserves. Additionally, do not skimp on lids; to prevent bulging and ensure long-term storage, use lids that are specifically designed for autoclaving.

22.08.2024

Author: UTEHO Editorial Team
Reviewed by: UTEHO Technical Department Specialists

UTEHO Expert Editorial Team

The UTEHO team develops autoclaves and accessories for home food preservation. All informational articles, guides, and recommendations are tested in real UTEHO autoclaves before publication.

Our content is based on practical experience, technical expertise, recommendations from UTEHO engineers and technologists, as well as feedback from our customers.

Practically tested in UTEHO autoclaves

Reviewed before publication

Content is regularly updated