Knowledgebase : Technical Information

When a young industrial engineer named Paul Van Achter perfected the technique of bonding stainless steel to copper in 1983 he was unaware that it was about to revolutionise the way copper cookware had been manufactured for more than 200 years.

Up until then, copper cookware was typically lined with a thin layer of tin, which while providing the necessary separation between the food being cooked and thermally conductive copper was by no means an ideal solution.&nbsp: Tin has a melting point of only 232 degrees Celsius making it unsuitable for cooking at high temperatures, and requires periodic, and expensive, relining.

Stainless steel on the other hand is practically indestructible, and is totally hygienic, but does not possess the same conductive properties of copper. &nbsp:The interior lining therefore had to be very thin (0.2mm) so as not to diminish the superior heat distribution and control, which had made copper cookware so highly regarded by chefs around the world.

Copper is a soft, or ductile, metal, which makes it is easy to shape with hand tools when heated. &nbsp:Stainless steel is much less ductile requiring specialist machinery to press and shape.

The major challenge faced by Paul when attempting to laminate a thin layer of stainless steel and a thick layer of copper plate was creating a permanent bond between the two very different metals, that would not separate when these were pressed to form the vessels of pots and pans.

The bond between the metals is created by pressing these together under very high pressure (850 tonnes/cm²) resulting in a metallic “intercristalline” connection.

Three years of trial and error finally resulted in the discovery of heat resistors, which when added to the lamination process, allowed the bimetal to be heated to a temperature high enough to obtain the required ductility for pressing.

The final result soon became the “gold standard” of cookware and was quickly adopted by the other manufacturers of high quality copper cookware who now use this same bimetal for their premium product lines.

Salt can react with any brand of stainless steel cookware, including the lining of Falk Culinair pots and pans, particularly when this is added to water at the start of the cooking process rather than when the water is boiling.

This is a form of corrosion and occurs due to the interaction of the chloride in salt, oxygen in water, and chromium in stainless steel.

It typically occurs when larger salt crystals, such as coarse sea salt, sink to the bottom of the pan before the water is heated and are allowed to react with the stainless steel lining while the water is heating.

The easiest way to prevent this from occurring is to wait until the liquid is simmering, or better still, boiling, to add your salt and then ensure it dissolves into the solution as quickly as possible by stirring.  At this temperature, there isn’t enough oxygen in the water for the reaction that causes pitting to take place.

The short answer to this question is ‘Yes, but not directly’.

To explain the solution, we first need to explain the difference between conventional and induction hobs.

Conventional gas and electric hobs use conduction to transfer heat into the body of the pots and pans, which then conducts this into your food.   As you might expect, the better the thermal conductivity of the cookware, the more efficient this process, which is precisely why copper cookware has been preferred by chefs and cooking enthusiasts alike for hundreds of years.

The induction process however is very different from conduction. Instead, electrical energy is transferred from large copper coil beneath the glass hob surface that incites alternating magnetic fields, which in turn induce secondary electrical currents, called ‘eddy currents’ in the pot.

As steel cookware is a poor conductor of heat, these eddy currents encounter resistance, and generate heat in the metal of the cookware itself, which is then transferred to the food it contains by conduction. This explains why an induction hob stays cool during use.

This is also the reason you have to use metal that is a poor conductor of heat on an induction hob.  Cookware suitable for induction hobs is made from ferromagnetic metal, such as cast iron, carbon steel or ferritic stainless steel.  Copper, although possessing excellent superior thermal conductive properties to these, is not ferromagnetic, and therefore unsuitable for direct use on induction hobs.

Now to the solution…  If a disc of ferrous metal, such as cast iron is placed between the induction hob and the copper cookware, this will generate heat by induction and then transfer that heat to the pan by conduction.

We therefore stock cast iron discs, for customers who want to use their copper cookware on an induction hob, which are available under the Accessories section in the product catalogue of our website.

The stainless steel layer in the Falk Culinair bimetal is only 0.2mm (200 microns) thick enough to prevent the contents of the pan reacting with the copper body without materially effecting the superior conductivity and distribution of heat in copper.  It is virtually indestructible, and unlike tin, requires no maintenance.

The stainless steel is “18/8” grade.  The number relates to the chromium and nickel contents of the steel, which are 18% chromium and 8% nickel respectively.

“18/8” is the most commonly used stainless steel.   This steel is known as 1.4301 in the European BS EN 10088 standard, or '304' (in the American AISI grade designation system).

It is an 'austenitic' type of stainless steel which is a high quality, sanitary, food grade stainless steel used in numerous food, dairy, brewing, hospital and sanitation applications all over the world.

The exact composition is:

IronChromiumNickelCarbonManganeseSiliconePhosphorusSulphurNitrogen
71.0% 18.0% 8.0% 0.08% 2.0% 0.75% 0.045% 0.03% 0.1%

Please note, there is no significant difference in the mechanical properties, or strength, between 18/8 and 18/10 stainless steels.  The 18/10 may be very slightly more ductile (i.e., slightly more able to bend without fracturing) than 18/8, but the difference is so minimal as to be completely inconsequential for our application.