Wednesday, April 04, 2007

School's In Session!

Hey Cheese Lovers,

Zoe Brickley, Murray's superstar affineur, is sitting you down for a serious lesson in cheese chemistry. Cheese is so much tastier when you understand what's going on deep down in those lactic molecules. Pencils out? Let's begin:

Chemistry of Ripening: The Cascade of Flavor

Three Main Processes

Glycolysis of Lactose- or the breaking down of milk sugars to lactic acid. Action is done
during primary fermentation by the starter culture. This is mainly a pre-aging process, though under the right conditions, starter cultures continue to affect acidity levels for several weeks.

Lipolysis- or the anaerobic fermentation or breakdown of butterfat to free fatty-acids
(FFA). These fatty acids directly contribute to flavor and texture. They also react with alcohols from primary fermentation to yield esters (flavor compounds). In some cases, like blue mold, the FFAs oxidize when the cheese is pierced and aerobically create fuel growth and create specific flavors.

FFAs are most abundant, or accumulate more in extra aged varieties of parmesan and some younger smear-ripened cheeses like Limburger. If lipolysis occurs too quickly or disproportionately to proteolysis, it can be a main reason for ‘off’ flavors and rancidity.

Lypolysis generally sets the stage for later reactions by creating new acids and alcohols. Unique flavors result from esters, alcohols, fatty and amino acids. The steps of cheesemaking and ageing must be carefully regulated to ensure that the correct ratio of reactions occur and yield consistent balances of flavor compounds, and thus the unique flavor and texture characteristics of each cheese type.

Proteolysis- or the anaerobic fermentation of milk proteins (caseins) to free amino acids
(FAA). This is the most important biochemical pathway for flavor and texture development. By products of proteolysis beside FAAs include other acids, alcohols, ammonia and sulfur compounds, and eventually esthers.

FAAs are not direct product of casein. First, casein is reduced to polypeptides, and then peptides, then finally to amino acids. Individual peptides are thought to contribute to the background flavor of many cheese families and may explain certain brothy, bitter, nutty and sweet tastes.

Original casein structure fixes water, making it unavailable for other reactions, and results in a drier appearance of the paste. Proteolysis releases the water from the casein structure explaining the ‘wetter’ appearance of well-ripened cheese, especially just below the surface of bloomy and smear-ripened cheese.

Sources for proteolytic and lipolytic enzymes:

Residual Coagulant: chymosin (animal rennet), pepsin, plant or fungal acids. The more coagulant that resides, correlated to more fixed moisture that will be gradually released as they go to work on the caseins over time. These coagulants are de-activated by high cooking temperatures, so residual coagulants are more important to raw and uncooked cheese types.

Starter Cultures
: These act on the peptides released from the caseins as well as on lactose. Normal salt content kills off starter cultures over time in aged cheeses, if left unchecked, they can cause over-acidification and undesirable flavor compounds. If too much salt is used, starter cultures never have a chance to kick-off the flavor cascade, resulting is a bland and dry cheese (salt is hydroscopic)

Secondary Innoculants
: B.Linens, P. Camemberit, Penicilium Candidium, Propionic Shermanii, Geo. Candidium. These are added to the milk at the time of coagulation, or applied to the surface of aging cheese. They are varieties of molds, yeasts and bacteria. Sensitive to environmental variables, they are intentionally added by the cheesemaker in order to precipitate specific flavor, texture, and aesthetic components in a finished cheese. Environmental requirements are considered in the Biochemical Pathway Matrix.

: an enzyme naturally occurring in milk, plays a secondary role in character formation to proteolysis. This variable, though, is difficult to control or duplicate industrially. Plasmin content and action is possibly, a reflection of milk quality, which is affected by animal health and terrior.

Non-Starter, Ambient, or Contaminant Microflora
: Undesireable growths are responsible for aesthetic flaws and some ‘off’-flavors. Some molds, yeasts and bacteria are naturally occurring in the ageing environment and positively contribute to cheese character and development. The environmental variables affecting ambient and contaminant growth is also considered in the Matrix.

Selective Agents for Microbial Activity (Environmental Variables):

pH: The pH levels during cheesemaking, and evolving levels during aging affect microbial, enyzymatic action, and thus cheese character. It should be noted that pH is closely related to calcium phosphate levels. Calcium is released from casein molecules after coagulation and later act as hydrogen (acid) sponges. Calcium and pH are usually positively correlated.

Moisture: Both the internal moisture of the cheese and external humidity are important for texture, flavor and rind development in a finished cheese. Often, cheeses with high internal moisture also have high acidity due to residual lactose from the whey, which ends up as lactic acid.

Salt: Salt content is important for the internal solution of the cheese as well as external applications and rind development. It can be applied in liquid form with brining, or as a dry rub. Salt can directly and indirectly affect all other selective agents. Keeping the right balance is extremely important for the cheesemaker and affineur.

Temperature: Temperatures during cooking and in the ageing environment are primary to microbial action. Excessive temperatures may foster contaminant and pathogenic growth, or simply overly-aggressive desirable growths. Lower temperatures can retard microbial action all-together.

Time: Lapses of time during cheesemaking, before and during curd separation, along with pressing affect most of the other environmental conditions. The length of affinage is integral to proper cheese development. An affineur must recognize when a more fragile, young cheese is ‘a-point.’ They must also know the optimal range for medium and extra aged cheese. These may become overly ammoniated, bitter or dry. Younger cheese rind growths may die, become too thick and unpalatable, or the cheese may lose textural integrity all-together.