Cheddar cheese is the most popular cheese consumed in the United States, with per capita consumption in 2001 of nearly 6 kg (12.7 pounds) per person per year (including other Cheddar types). Approximately 1.2 billion Kg (2.7 billion pounds) are produced each year in the United States. Several cheeses, including Colby, Monterey Jack, and other washed or stirred curd cheeses, are closely related to Cheddar cheese and are collectively considered as American type cheeses. However, this designation can be confusing since American cheese is often considered synonymous with processed American cheese, a totally different product.
Cheddar cheese was first made in the village of Cheddar, England. It is different from most cheeses due to a specific curd handling technique called Cheddaring. During Cheddaring, the curds are separated from the whey and allowed to mat, after which the matted curd slabs are flipped and stacked. The Cheddaring practice, like many great discoveries, probably occurred as a result of an accident. Perhaps the cheese maker had drained the whey, and instead of stirring the curds prior to filling forms or hoops, he or she was delayed or distracted. The curds then matted, staying warmer than usual, and then began to stretch and become plastic. The cheese that was then produced had a unique texture and body that led to the adoption of the Cheddaring process.The manufacture of Cheddar cheese has evolved from a traditional, strictly batch operation to a more modern process that is more automated and mechanized.
The early steps in Cheddar cheese manufacture are rather straightforward. Whole milk, either pasteurized or raw, is brought to a temperature of 30°C to 32°C, and is inoculated with a mesophilic lactic culture containing strains of L. lactis subsp. lactis and L. lactis subsp. cre-moris. The culture, or rather the specific strains present in that culture, is selected based on the desired properties expected in the finished cheese. Sometimes S. thermophilus strains are added to promote rapid acidification. If the cheese is intended for the process market, then speed is the main criteria, and fast-growing strains of L. lactis subsp. lactis are often used. If, however, the cheese is to be aged, then appropriate flavor development will likely drive selection of the culture (usually containing L. lactis subsp. cremoris).Two properties, however, are required: the strains must ferment lactose and they must be able to hy-drolyze and use proteins as a nitrogen source. Of course, other properties, as well as the form of the culture (whether bulk set or direct-to-vat set, frozen or lyophilized, mixed or defined) are also important, and are discussed later in this chapter.After culture addition, chymosin is added, coagulation occurs, and the curd is cut using medium sized knives (giving curds about 0.6 to 0.8 cm in diameter). Following a short five- to ten-minute "healing"period to allow the curds to form, the curds are gently stirred. Heat is then applied gradually, about 0.3 degrees per minute, to a final curd-whey temperature of about 38°C or 39°C. As the curds are cooked, the stirring speed is increased to promote heat transfer, and stirring is maintained for an additional forty-five minutes. Although the starter culture bacteria are contained within the curd, as a general rule, little fermentation should occur during the cooking or stir-out steps. A decrease of only 0.1 to 0.2 pH units is normal.Although L. lactis subsp. lactis has a slightly higher temperature range for growth compared to L. lactis subsp. cremoris, both grow slowly, if at all, at the upper end of common cooking temperatures. If however, lower cooking temperatures are used, growth of the culture can occur, resulting in fermentation and lactic acid formation. Although fermentation during this step may be desirable for some cheeses, for Cheddar it generally is not. This is because acidification is accompanied by demineralization of casein as the calcium becomes solubilized. When the whey is drained, the remaining curds contain less calcium, resulting in cheese that holds fat poorly and is less elastic, with a short, brittle texture. The importance of calcium during later stages of the Cheddar process is discussed below.
Once most of the whey is drained, the curds are assembled on both sides of the vat, where they quickly mat or stick together. By the time the last of the whey is removed, the curds have turned into a cohesive mass. A knife is then used to cut the matted curds into approximately 20 cm x 80 cm slabs. Depending on the cheese maker's preferences, the slabs are then either rotated or flipped or flipped and stacked, a process known as Cheddaring. Because the temperature of the Cheddar slabs is maintained at 28°C to 32°C, the culture can begin to grow in earnest, increasing from about 106/g to 108/g of curd within the Cheddaring period. As the lactic culture grows, it performs two critical functions. First, it ferments lactose in the curd, in homolactic fashion, to lactic acid. Second, it hydrolyzes casein via a cell wall-anchored pro teinase, forming a variety of variously sized pep-tides.The consequences of both of these activities will be discussed below.
During the Cheddar process, several biological, chemical, and physical changes occur that give this cheese it's characteristic properties. However, without an active starter culture, none of these changes will occur. As the culture produces lactic acid and as pH becomes more acidic, calcium that was initially associated with the negatively-charged amino acid residues of casein (e.g., serine phosphate) is displaced by protons. In this state, the casein is more soluble, smooth, and elastic, as is evident as the Cheddar slabs stretch and become plastic-like. Eventually, however, if the pH of the cheese becomes too acidic (less than 4.95), the cheese will become short and crumbly. Fermentation during Ched-daring, what Cheddar masters refer to as dry acid, is much preferred over acid formation during the cooking step, or wet acid development. In addition to the changes in casein structure that occur as a result of acid formation, gravitational forces from stacking the Cheddar slabs on top of one another also affect cheese structure. This facilitates linearization and stretching of the casein and allows the curds to knit when pressed (see below).
The longer the cheese is Cheddared, the more the culture will grow and with it, the greater will be the acidity. The extent of Ched-daring, and with it the extent of acid formation, depends, therefore, on the desired properties of the finished cheese. Lactic acid levels of 0.4% to 0.6% are normally achieved by the end of Cheddaring (about one and a half to two hours after whey separation), resulting in a finished cheese pH of 5.0 to 5.2. In addition, longer Cheddaring times also result in more cell mass produced. Since the lactic acid bacteria in the culture produce enzymes that degrade milk proteins, higher concentrations in the curd at this stage likely results in greater proteolysis at later stages, i.e., during ripening.
Although the traditional Cheddar process is still practiced in the United States in small cheese factories, most mid-sized and large operations use different procedures and produce a somewhat different type of product. This is because large cheese factories require much greater throughput than can be obtained by traditional procedures. Thus, setting, coagulation, and cutting steps are performed in enclosed vats, and the cut curds are then pumped to another location for further processing.This allows the manufacturer to clean, sanitize, and re-fill the original vat.
In addition, modern operations have eliminated the labor-intensive flipping and stacking Cheddaring steps by employing alternative methods. Cheese makers learned that a similar texture could be obtained if the dry curds, after draining,were simply stirred in the vat.An additional variation of this process involves adding cold water to the curds. As noted above, this step results in less lactose in the curd, and it also increases the moisture. The resulting cheese, known as Colby, is a less acidic, high moisture cheese, compared to traditional Cheddar. In some modern cheese factories, curds are continuously conveyed to the top of Cheddar-ing towers. By the time the curds have descended from these vertical towers and emerge out at the bottom, they have achieved a similar level of Cheddaring as traditional curd.
After Cheddaring, or when the pH is about 5.2 to 5.4, the plastic, elongated Cheddar slabs are chopped up in a special milling device (called, appropriately, a Cheddar mill) to reduce the slabs to uniform, thumb-sized pieces.These Cheddar curds are bland, with a squeaky, rubbery texture. Next, salt is applied, in an amount ranging from 2% to 3%, and in a manner that permits even salt distribution (i.e., while the curds are continuously being stirred).
Salting is a critical step, since it has a profound effect on the quality of the finished cheese. This is because, in addition to providing flavor, salt has a major influence on controlling microbial and enzymatic activities in the ripening cheese.Although 2% salt might not be expected to have much of an effect on microorganisms or enzymes in food, one must consider that cheese consists of two phases, a fat phase and a water phase. It is in the water phase that the salt is dissolved, and likewise, that is where the microorganisms live. Since Cheddar cheese contains no more than 39% water, the relevant salt concentration, i.e., that with which the microorganisms must contend, will be more than 5% (2/39 X 100 = 5.1%).At this concentration, the growth of the starter culture bacteria and many other microorganisms and the activities of microbial and milk-derived enzymes are effectively controlled. This is not to imply that microbial and enzymatic activities are actually halted, because salt-tolerant organisms and enzymes remain active in the presence of high salt concentrations. Rather, the salt provides a means to check or contain those activities and to create a selective environment that aids in establishing a desired microflora.
The active salt concentration is often referred to by cheese manufacturers as the salt-in-moisture or S/M ratio. For example, a cheese with 2.4% salt at a moisture of 38% will have a S/M of 6.3.The S/M value is arguably the main determinant affecting cheese ripening. The higher the S/M level, the more inhibitory will that environment be to microorganisms and enzymes. In contrast, for cheeses having low S/M values (i.e.,below 4.5),the microflora will not be effectively constrained or controlled and production of off-flavors and other spoilage defects may occur. However, cheese ripening rates, which are also a function of mi-crobial and enzymatic activities, will also be inhibited if the S/M is too high. Thus, cheese manufacturers must carefully adjust salt concentrations and moisture levels (as well as pH) to achieve the desired ripened cheese properties (Figure 5-6). In general, an S/M between 4.5 and 5.0 is desirable.
The next step involves filling forms, hoops, or barrels with the salted curds. The size of these forms range from 9 Kg to as high as 290 Kg (20 pounds to 640 pounds). Obviously, the form also gives shape to the cheese, varying from rectangular blocks to barrels. Many of the cheese forms have collapsible ends, such that pressure can be applied to enhance the transformation of the curds into a solid mass and to squeeze out whey (through perforations in the
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