The invention concerns a container for food products or other sensitive products, said container being made of a material that intends to provide the container with gas-tight properties and that comprises a layer that exhibits no or only a low translucence to light. The invention is characterized in that at least one opening is provided in the layer with no or low light translucence such as to allow light for non-destructive detection of gas inside the container to enter and exit through said at least one opening. The invention also concerns a method for detecting gas inside a sealed container of the above type and a method for manufacturing of a container of the above type from blanks of a cardboard based material. The invention also concerns a production system comprising an apparatus for filling containers of the above type with a product and an apparatus for sealing the filled containers, wherein the system further comprises an apparatus for carrying out the method for detecting gas inside the sealed container.