Is the ‘Pinch Test’ an Accurate Test for Testing the Quality of Silicone Kitchenware ?

It is in a way, but not how and why everyone thinks it is. Many people believe that when you twist or pinch silicone kitchenware, if it displays ‘white’ then the silicone contains fillers and is therefore not safe or a good quality silicone. This part is not quite accurate and I have confirmed this with suppliers of silicone raw material and manufacturers of silicone kitchenware (including my own).

Let me explain…

Silicone is made from quartz sand and oxygen atoms combined with carbon, hydrogen and sometimes other elements. However pure silicone in this form is hard for moulding into products and therefore fillers need to be added. So yes, silicone kitchenware will have fillers (curatives) added however this does not mean the silicone material is unsafe. This is where the passing of testing standards to ensure the silicone material is food safe comes in.

The two main tests are FDA & LFGB testing (I have written another blog post explaining the difference between the two).

So where does the white come from?

First of all, I need to explain that depending on the shape and productivity of the silicone product to be produced, a different manufacturing process may be used. One of the predominant processes used is called ‘HTV’ or High Temperature Vulcanisation.

Vulcanization is the chemical process of converting rubber into extremely durable materials by the use of heat. It also involves heating the rubber with sulfur or other curatives (fillers) to modify the polymer to form cross-links. Silicone kitchenware cured using this process may succumb to whitening when being pinched because of one or more of the following reasons:

Improper adjustment of raw materials for mixing silica gel and vulcanizing agent;
The vulcanization temperature of silicone products is too high, which causes polymer degradation and frost;
The vulcanization temperature of silicone products is too low, and local areas are not completely vulcanized, which causes whitening and frost;
The temperature is too high when mixing silicone rubber;
Added impurities such as powder glue.

What about odour?

The odour of silicone mainly comes from the vulcanizer added. Normally the vulcanzier should be volatilized during mold production, but sometimes there may be residue which makes the silicone smelly. By using better vulcanizer such as Platinum or taking better post cure, the residue will be eliminated and the products will be odorless.

Back to LFGB quality silicone

Silicone kitchenware that is made from LFGB approved silicone is composed of a different raw silicone material than FDA silicone but it has also gone through the vulcanization process twice thereby greatly reducing the reasons mentioned above that might cause the ‘whitening’ to occur when pinched. It also results in less odour.

To this end, as we at Just Smart Kitchenware care deeply about the health of our customers, we ensure our compact and collapsible silicone products are produced to the highest quality using LFGB certified silicone. You can feel confident in choosing JSK for your collapsible containers not only because of the quality but also for their other differing qualities as outlined in our Best Collapsible Containers & Why That Is article.