THE RIPENING OF A CAMEMBERT
The ripening process of cheese is very complex and involves microbiological and biochemical changes to the curd resulting in the ﬂavor and texture characteristic of the particular variety.
Dairy fermentations involve microbial interactions at several levels. These interactions lead to different microbiota playing their role in a succession important to the progress of the fermentation and the quality of the final product. They take place in the form of complex interactions between the starter culture, yeast and microflora in mold-ripened cheeses
The Flora of Camembert Cheese
Although a considerable variety of molds and fungi has been observed on Camembert cheeses, a list of possibly twenty species would include those which were often found. Among these are perhaps six species of Penicillium, two or three of Aspergillus, Geotrichum candidum (previously known as Oidium lactis), Cladosporium herbarum, one or two of Mucor, one or more of Fusarium, Monilia candida, and two species perhaps related to it, with the incidental occurrence of Acrostalagmus cinnabarinus, a Cephalosporium, various species of Alternaria, and Stysanus. Besides these, yeasts such as Kluyveromyces lactis were found in large numbers and considerable variety in many cases.
We are just going to focus mainly on P. camemberti and G. candidum whose mycelium development is responsible for the bloomy aspect of Camembert-type cheese.
It has been noted that G. candidum is abundant upon every brand of Camembert. The wide genotypic and phenotypic diversity of Geotrichum candidum strains…[and] G. candidum possesses many different metabolic pathways that are of particular interest to the dairy industry. G. candidum is of importance in the maturation of cheese, and much is known about its direct contribution to cheese ripening and flavour formation. Its diverse metabolic potential means that G. candidum can play an important role in the ripening of many soft and semi-hard cheeses and make a positive contribution to the development of taste and aroma. It may also influence the growth of other microorganisms, both valuable and detrimental. The significance of the presence of G. candidum in cheese depends on the particular type of production and on the presence of biotypes featuring specific types of metabolism. However, in situ metabolic pathways involved in cheese ripening and their regulations are mainly unknown (Boutrou, Guéguen)
The comparison of the results by a 1906 study done by Charles Thom, mycologist in Cheese Investigations in the Dairy Division of the Bureau of Animal Industry, showed that a single species of Penicillium was present upon every Camembert cheese that was examined and in partially ripened cheeses this mold often covered the majority of the cheese surface. This mold is known as “Penicillium Camemberti” or the “Camembert mold.” This species develops a large and characteristic growth of aerial mycelium in addition to a densely felted mass of white threads which penetrate the surface of the cheese for 1 or 2 mm. and largely constitute the rind.
During aging, Geotrichum candidum and yeasts grow initially, but they are soon followed by a dense growth of Penicillium camemberti:
Salts migrating to the rind
Salts are ionic compounds that result from the neutralization reaction of an acid and a base. Both lactate, from lactic acid, and Calcium (Ca) and Phosphate (PO4) are defined in chemistry as salts. P. camemberti and G. candidum oxidatively metabolise lactate to CO2 and water, deacidifying the cheese surface and resulting in a higher pH at the rind of the cheese. This deacidiﬁcation causes a pH gradient to develop from the center of the cheese to its surface and this established pH gradient of decreasing values towards the center of the cheese causes lactate to migrate towards the surface where it is used as a carbon source by P. camemberti. As the cheese continues to age and the microbes continue to metabolize, pH increases to about 7.0 in the outer part of the cheese and about 5.5 in the centre. The change of pH is most pronounced on the surface of the cheese, which is covered by the white mycelium of the P. camemberti after a week of maturation. When lactate becomes depleted, casein, a milk protein, is then metabolised.
Calcium phosphate, found in high quantities in or on the casein micelles, is also soluble in acid environments, and as the pH of the surface of the cheese decreases, calcium phosphate migrates towards the surface of the cheese, where it then precipitates as a layer of Ca3 (PO4)2. This migration results in a calcium phosphate gradient from centre to surface and the depletion of calcium phosphate in the center of the cheese assists in the development of the desired soft texture of the cheese. Reduction in the concentration of calcium phosphate, together with increased pH and proteolysis (the breakdown of proteins – casein proteins in this case) results in softening of the interior, which is characteristic of mature Camembert-type cheese.
Further metabolisation of casein results in the formation of ammonia from amino acids. In very mature cheese, ammonia is produced at the surface from proteins and diffuses into the curd. A cheese that smells very strongly of ammonia is extremely old and probably should not be eaten.
Enzymes migrating into the paste
The proteinases (enzyme that conducts proteolysis) from P. camemberti migrate very slowly into the cheese, and only reach a depth of about 6mm from the surface. This means that their direct participation in the enzymatic reactions deep in the interior of the cheese is limited. The important enzymatic activities in the interior of the cheese are caused by the enzymes from the rennet, the plasmin from the milk and enzymes from the lactic acid starter cultures.
The French have been producing Camembert cheese for hundreds of years. The creamy consistency and delicious, earthy flavors (flavor chemistry is a post I hope to tackle soon) all result from ambient fungi. While it is true that some cheesemakers spray the necessary fungi on their cheeses in the aging caves, there are still many that allow the fungi to settle naturally to ripen the cheese. It is interesting to me – and I hope I have enlightened you as well – about what you’re eating and the relationship between you and the fungi on the cheeses you love. The research on cheese microflora continues today – there are many studies and unanswered questions.
Marie-Hélène Lessard, Gaétan Bélanger, Daniel St-Gelais, and Steve Labrie. The Composition of Camembert Cheese-Ripening Cultures Modulates both Mycelial Growth and Appearance. Appl Environ Microbiol. 2012 March; 78(6): 1813–1819. doi: 10.1128/AEM.06645-11 http://www.ncbi.nlm.nih.gov/pubmed/22247164 last accessed: 11/16/2012
Paul L. H. McSweeney, Biochemistry of Cheese Ripening, Vol 57, No 2/3 May/August 2004 International Journal of Dairy Technology. Dept. of Food and Nutritional Sciences, University College, Cork, Ireland. http://comenius.susqu.edu/biol/312/biochemistryofcheeseripening.pdf last accessed: 11/16/2012
Herbert William Conn. The Camembert Type of Soft Cheese in the United States. U.S. Department of Agriculture, Bureau of Animal Industry, Bulletin No. 75. 1905
Karl Esser, ed. The Mycota: A Comprehensive Treatise on Fungi as Experimental Systems for Basic and Applied Research: Industrial Applications X, 2nd ed. Dec 1, 2010
Boutrou R, Guéguen M. Interests in Geotrichum candidum for Cheese Technology Int J Food Microbiol. 2005 Jun 25;102(1):1-20.