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Cleaning and Sanitation
Material and Corrosion Resistance
Stainless Steel
The corrosion inhibitor in stainless steel is the passive oxide layer that protects the surface. Beerstone (calcium oxalate) can cause corrosion if not removed, because the metal beneath the deposit becomes oxygen-depleted. Many types of stainless steel exist. The type of stainless steel used in brewing and fermentation equipment is the nonmagnetic 300 series, which includes several types. Those more common to brewing are 304 and 316 stainless steel. Kegs are usually made from these materials. Types 304 and 316 have very good corrosion-resistant properties and are easily welded (24). Other 300 series metals are to be avoided for brewery use, especially 303.
Copper
Copper generally is more acid-resistant than alkaline-resistant. Copper is usually resistant to nonoxidizing acids such as acetic, hydrochloric, and phosphoric, but is not resistant to oxidizing acids such as nitric and sulfuric nor to nonoxidizing acid solutions that have oxygen dissolved in them (27). Alkaline detergents will blacken copper due to the formation of oxides. Commercial detergents usually contain buffering agents and inhibitors that prevent corrosion of copper.
Aluminum
Caustic cleaners react with aluminum, actually dissolving the metal and pitting the surface. The reaction with aluminum can produce a potentially dangerous situation, in that flammable hydrogen gas is produced. Proper ventilation is necessary under these conditions. The unsightly pitting that can occur can be a good harboring point for bacteria.
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