Material and Corrosion Resistance

Stainless Steel

Many types of stainless steel are used in brewing beer. 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 316L stainless steel. Types 304 and 316L have very good corrosion-resistant properties and are easily welded. Most brewery equipment is constructed from Type 304 stainless steel. Type 316L, which has better corrosion resistance properties, is often used but the material cost is much higher. Other 300 series metals are to be avoided for brewery use, especially 303.

• Chemical Agents

Acid Detergents - Some acids can be used for a variety of stainless steel cleaning and removing beerstone.

Alkaline Detergents - Sodium hydroxide, commonly used in the CIP systems of commercial breweries, is quite effective for removing organic deposits from stainless surfaces.

Alkaline Disinfectants - Alkaline disinfectants, e.g., sodium hypochlorite, do not corrode stainless steel Type 316.

• Passivation

As mentioned, stainless steel's resistance to corrosion and discoloration is in part due to a passive oxide layer that protects the metal. The oxide forms naturally on clean surfaces exposed to the atmosphere, but this formation can take up to two weeks, which is too long for breweries. A technique known as passivation, using acid mixtures containing oxidizing agents, can be used to enhance the formation of the passive oxide layer.

Copper

Copper generally is more acid-resistant than alkaline-resistant. Copper is usually resistant to non-oxidizing acids such as acetic, hydrochloric, and phosphoric, but is not resistant to oxidizing acids such as nitric and sulfuric or to non-oxidizing acid solutions that have oxygen dissolved in them.

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.