BASE

The base is primarily responsible for the heat exchange between the heat source and food. To cook at a stable temperature, it is best if this is able to store large amounts of heat, while the opposite is true if it is necessary to cool food rapidly (e.g. in the cooking of sugar).

As we have seen above, the materials used for the manufacture of cookware have very different reactions to heat. Copper and aluminium offer great thermal conductivity properties, providing a fast and even distribution of heat throughout the receptacle, but with the disadvantage of maintaining that heat for a short time. We have already mentioned that stainless steel has low thermal conductivity. Therefore, the containers made with this material have a base known as a “thermal diffuser”, colloquially known as the “sandwich” base, which is intended to compensate for the low conductivity of steel.

IT IS A SUPPLEMENTARY BASE FORMED BY A THICK ALUMINIUM LAMINATE. WE SHOULD ENSURE THAT THIS BASE IS OF THE CORRECT THICKNESS IN ORDER TO OFFER LASTING RESULTS (BETWEEN 2.5 AND 5 MM FOR DOMESTIC COOKWARE, AND BETWEEN 5 AND 10 MM FOR PROFESSIONAL USE RECEPTACLES). THIS BASE IS ALSO PROTECTED BY A THIN STAINLESS-STEEL SHEET, CREATING, TOGETHER WITH THE MATERIAL OF THE BASE OF THE RECEPTACLE, A “SANDWICH” OF MATERIALS (STAINLESS STEEL + ALUMINIUM + STAINLESS STEEL), HENCE ITS NAME.

This marriage between aluminium and stainless steel is no easy task, as we are joining two materials that react differently to heat. This implies that, on occasions, the thermal diffusing base can come apart. This is why the welding process of the different materials is very important in order to prevent them separating.

The most reliable process for making this bond is what is called friction or impact welding. This technique involves preheating the components that form the thermal diffusing base (stainless steel + aluminium + stainless steel) and subjecting them to high pressure. The aluminium part expands and is welded to the other materials, making them practically impossible to separate.

Returning to the composition of the “sandwich” base, usually the stainless-steel sheet that protects the aluminium layer is of a different alloy than that used in the manufacture of the cookware body (18/10 stainless steel). It is a stainless steel with a higher iron content and with a low percentage of nickel or none at all, which gives it magnetic properties that make it suitable for induction cookers. This alloy is known as ferritic stainless steel, 18/0 or AISI 430.

The protective sheet on the base, known as encapsulation, can cover the entire surface of aluminium including the sides or it can protect only the base of the aluminium disc, in this case we will talk about a “technical” base.

We talk about an encapsulated diffusing base when the ferritic stainless-steel sheet covers the entire aluminium section, including the sides. It is a cap or capsule that protects the entire diffuser bottom.

With an encapsulated base, we cannot see the aluminium inner part, which means that we cannot see if it covers the entire cavity.

Where the aluminium inner part does not cover the entire inside of the capsule or simply does not exist inside, it creates an effect contrary to the idea of the sandwich base, as with the absence of all or part of the aluminium, an air space is created inside which acts as an insulator and which makes it even more difficult to transmit heat throughout the vessel.

This malpractice is not usual, but in some cases it is done in order to lower manufacturing costs which, as we mentioned above, can lead to problems of efficiency.