Entstehung und Aufbau farbiger schichten auf rostfreiem stahl: I. Verfärbungen beim Kochen von Nahrungsmitteln

Formation and structure of coloured layers on stainless steel: I. Discolorations by cooking of food Upon cooking of vegetables and other food coloured layers can be formed on stainless steel. By cooking tests, AES-studies of the formed layers and by electrochemical experiments the formation of these layers was simulated and their structure was elucidated. By the process of oxygen corrosion OH^? ions are formed near the surface of the steel, precipitation of Mg(OH)² is caused which is bound to the surface together with silicates and phosphates. The layer is 100 to 200 Å thick and appears coloured by built-in ions of the alloy metals. The ions needed for formation of the layers, Mg²⁺, SiO₃^2? and PO₄^3?, all are present in tap water, thus the formation of such layers can occur always upon cooking and is only intensified by substances from the food (phosphates). The use of steels which are more corrosion-resistant or the precipitation or complex formation of the above mentioned ions or the exclusion of oxygen during cooking would prohibit the layer formation. However, such measures are hardly feasible and they are even unnecessary since the described process is harmless concerning hygienic aspects.