What Does Beerstone Scale Mean?
Beerstone scale is a grayish-brown scale composed of calcium oxalate (CaC2O4) and organic substances forming on the inside surfaces of a brewing apparatus.
Beerstone scale forms in aging tanks, serving tanks and kegs. It can be incredibly difficult to remove, especially after the buildup becomes visible to the naked eye.
Removing beerstone scale is a time-consuming and costly process. If it is not completely removed in the cleaning process, beerstone can cause an unsanitary surface that can harbor microorganisms.
Corrosionpedia Explains Beerstone Scale
In the brewing industry, calcium oxalate is a precipitate. This precipitate is largely due to a reaction between alkaline cleaners (caustic), hard water minerals (calcium and magnesium) and protein (amino acids). If left unchecked, beerstone can have disastrous consequences for the beer.
Beerstone scale causes corrosion. The metal underneath the deposit can become oxygen depleted via biological or chemical action and lose passivity, becoming pitted. This is one reason why the removal of beerstone is important. A two-step procedure is most effective for removing beerstone. Beerstone is a combination of protein buildup and mineral deposit, so removal works best if the protein is broken up with a caustic, like sodium hydroxide, and then the remaining lime can be dissolved by an acidic cleaner. Once free of beerstone, metal surfaces typically require less aggressive chemicals to keep the problem from reoccurring.
However, one of the procedures used can lead to further trouble. Hydrochloric acid, for example, is an excellent acid for removing calcium-based scale. It is imperative to thoroughly rinse the vessel if this acid is used to remove scale. Otherwise, it can cause corrosion to stainless steel and lead to pitting. Phosphoric acid is a much better choice as it does not attack the steel.