Brewery Cleaning And Sanitation
Material Corrosion Resistance
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.
Acid Detergents. Some acids can be used for a variety of stainless-steel cleaning and removing beerstone. Phosphoric and nitric acids are the preferred choice because they do not attack stainless steel, though nitric acid is considered best.
Alkaline Detergents. Sodium hydroxide, commonly used in the CIP systems of commercial breweries, is quite effective for removing organic deposits from stainless surfaces.
Peroxyacetic acid (peracetic, PAA) has been known for its germicidal properties for a long time. Peroxyacetic acid is gaining popularity as a sanitizing agent in the beer industry for its broad microbicidal capacity, and rapid, on-contact efficacy under a range of conditions. It can be used to sanitize a range of surfaces and equipment, including tanks, pumps, lines, and filters, and is non-corrosive to stainless steel at the dilute usage concentrations. It is suitable for use in a final CIP rinse; no further rinsing is required.
Alkaline Disinfectants. Alkaline disinfectants, e.g., sodium hypochlorite, do not corrode stainless steel Type 316 if used at the correct concentrations and temperatures. However, when these disinfectants are exposed to Type 304 stainless steel, which are less resistant, temperatures should be restricted to 60 degrees C (140°F) and concentrations to 250 mg/L (Hough et al., 1982).
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 chromium oxide layer.
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.
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.
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