The Science of Cream Lines
We all recognize the ripening pattern of cheeses such as brie, Champlain Valley Triple Cream
, Humboldt Fog
, and Greensward
: as the cheese matures, a gooey layer forms just under the rind, with the center remaining solid. This gooey layer is referred to as the cream line. Most bloomy cheeses are at peak when the cream line is distinct from the firmer center. However, in cheeses such as Greensward
, the goal is to allow the entire cheese to turn into a cream line, so that the final texture is fudgy and spoonable.
A piece of Humblot Fog with robust cream lines
How exactly does the cream line develop?
The cheese surface microbes are major workhorses in the ripening process of cheeses that develop cream lines. When the cheese is initially made, its pH is relatively quite low (i.e., acidic) due to the presence of lactic acid that had been produced by starter cultures. In the case of bloomy rinded cheeses, molds such as Penicillium candidum (white furry mold) or the mold-like yeast Geotrichum candidum (wrinkly brainy appearance) busily work on the surface to break down the lactic acid and protein.
Vermont Creamery Coupole, a cheese with a Geotrichum candidum rind
Sometimes we help jump start mold growth, by coating the exterior of a young cheese with a layer of vegetable ash which helps to decrease acid levels. This is why Loire Valley varieties such as Selles Sur Cher
, and St. Maure
are grey—the Geotrichum isn’t completely opaque, and grows through the ash layer. Conversely, Penicillium candidum is an opaque mold, so the outer ash layer on Humboldt Fog
or Haystack Peak
is visible when a cross section of a mature rind is cut.
Murray’s St. Maure, with its visible ash line below the rind
In rennet-set cheeses, calcium phosphate functions as glue that holds the casein structure together in the matrix. As the lactic acid is metabolized, pH increases, and calcium phosphate loses solubility. Calcium phosphate maintains equilibrium in the matrix, and gradually migrates to the surface as the pH increases. Fun fact: the calcium phosphate that migrates out of the matrix precipitates on the cheese rind. So the rind is extra nutritious!
Casein is hydrolyzed during early stages of protein breakdown, and the end products possess different water-binding (water activity) abilities. The changing water activity of the matrix, coupled with decreased levels of “glue,” results in softening. Over time, the softened portion (cream line) expands, from the outer portion beneath the rind towards the cheese center. Catabolism of both protein and lipid by surface microbes releases end products into the matrix, such as ammonia, amino acids, and fatty acids. Further breakdown of amino or fatty acids result in flavor or aroma compounds, such as methional (boiled potatoes, derived from the amino acid methionine). Cream line development continues after a cheese is wrapped and placed in refrigeration, which is why Greensward
ideally will sit in cold storage for a few weeks prior to release to ensure complete breakdown of the matrix.
With acid-set cheeses, the mineral content is very low. Much of the calcium in the casein micelles was solubilized as the acid level increased in the milk during the cheesemaking process. As a result, there is very little “glue” in the matrix—which is why the texture of these cheeses is short and crumbly, such as with chevre and the Loire Valley varieties. For these cheeses (e.g., Valencay
), the surface mold increases the pH, which in turn increases interactions between casein and water. The “hydrated” casein is the cream line.