Cleaners are great for removing hard organic soils from the surface of stainless steel brewing tanks, but require an additional acid cycle to remove inorganic materials that may be hidden in the pores of your stainless steel that standard cleaners are too large to penetrate. In addition, most cleaners are very viscous and even after a good hot water rinse, there may still be residue inside. An acid cycle will remove inorganic solids, beer stones, hard water, minerals and residue left behind from the initial cleaning cycle.
When using an approved inorganic mixture, the addition of the acid cycle will also add a protective passivation layer to the stainless steel surface of the fermenter. This additional step can add extra life to your brewery tanks. How often? Ideally every time, but if cost is an issue, then every three cleaning cycles.
(Passivation – The removal of free iron particles or iron compounds from the stainless steel surface of the brewery tank by chemical dissolution, most typically by treatment with an acid solution.)