The first article I am going to take a look at is “The Chemistry of Camembert.” Camembert is a type of surface-ripened cheese. Unlike many other cheeses that ripen from the inside out, camembert ripens from the outside in, forming a layer of mold on the outside. This surface-ripened process is specific to soft cheeses like brie, cambozola, and man goat cheeses. In order to give camembert its unique taste and texture, it is sprayed with the mold, Penicillium camemberti and Geotrichum candidum, and left to sit for about 3 weeks. These bacteria break down the lactic acid from the cow’s milk into water and CO2. This reduces the acidity of the cheese and draws more lactic acid to the surface, where it is again consumed by the bacteria. The pH levels rise from about 4.7 to about 7.0 during this process. The rise in pH also causes calcium phosphate to precipitate out of the cheese at the surface. This causes the cheese to become very soft.
The second article I will cover is “The Chemistry of Limescale.” To start off, water hardness is the presence of large amounts of calcium and magnesium ions in water either in the form of bicarbonates or sulfates. If bicarbonates are present, the problem can be fixed by boiling the water. If sulfates are present =, there needs to be a more complicated solution. Much like the calcium phosphate precipitating due to a lower solubility in high pH, heating the water causes the bicarbonates to become more soluble and therefore decomposing the limescale. However, this does not work with sulfates, because they do not dissolve as well when heated. There are several methods to treat this type of hard water. The first is using ion exchange resin. This replaces the calcium and magnesium ions with harmless sodium ions. This is used in appliances like dishwashers. The second method is the use of acids, sometimes strong acids, to break up the limescale. For example, HCl is used in toilets to break up limescale. You may also use citric acid in kitchen appliances.
Both of these articles relate to the solutions, but more specifically the changing of what is in a solution via chemical reaction. You can change the contents of a solution by adding substances that react with the ions present. This results in a precipitation or pH change. The lactic acid in camembert cheese is consumed by the bacteria causing the pH levels to rise, which in turn causes the precipitation of the calcium phosphate. This gives the cheese its soft texture. Limescale is removed by adding acids, which lower the pH levels and break up the hard compound.