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1MesophiIic cultures = Lactococcus lactis subsp. lactis and Lactococcus lactis subsp. cremoris

2Thermophilic cultures = Streptococcus thermophilus, Lactobacillus delbrueckii subsp. bulgaricus, and/or Lactobacillus helveticus 3Citate-fermenting Leuconostoc or Lactococcus sp. may be added 4Streptococcus thermophilus may be added

5For Limburger and other surface-ripened cheeses, species of Arthrobacter, Micrococcus, and yeasts may also be present. Data from Guinee and Fox, 2004;Marcos et al., 1981; and other sources

1MesophiIic cultures = Lactococcus lactis subsp. lactis and Lactococcus lactis subsp. cremoris

2Thermophilic cultures = Streptococcus thermophilus, Lactobacillus delbrueckii subsp. bulgaricus, and/or Lactobacillus helveticus 3Citate-fermenting Leuconostoc or Lactococcus sp. may be added 4Streptococcus thermophilus may be added

5For Limburger and other surface-ripened cheeses, species of Arthrobacter, Micrococcus, and yeasts may also be present. Data from Guinee and Fox, 2004;Marcos et al., 1981; and other sources

In contrast, if a 1% inoculum is added and the incubation temperature is set at 20°C to 22°C, well below the optimum for growth (essentially, room temperature), coagulation may take twelve to sixteen hours. Thus, a busy cheese maker could, under the first scenario, produce multiple batches of cheese each day out of the same vat. However, it is also possible, in the alternative procedure, to inoculate or set the milk at 5:00 p.m., go home, sleep, and return to work early the next morning and have the cheese ready for the next step. Of course, inoculum and temperature regimens in between the long-set and short-set make times are also possible. Finally, although not required for coagulation, a small amount of chymosin (1 to 2 ml per 1,000 Kg) is sometimes added to promote a more firm coagulum (usually for large curd cottage cheese).

Once a pH of about 4.7 is obtained, a soft curded gel mass is formed.The gel is then cut using a pair of cheese knives that resemble square or horizontal-shaped harps. One knife contains vertical wires, and the other horizontal wires.The distance between the wires determines the curd size, which in turn depends on the product being made (e.g., large, medium, or small curd Cottage cheese products are available). Following the appropriate passes through the gel, die-shaped cubes are formed.

Almost immediately, whey becomes apparent and the curds begin to separate. The curds after cutting are very soft and fragile, and must be handled carefully to avoid shattering or fracture. Not only do fractured curds result in product defects, but, importantly, the small, broken curds or "fines" are lost when the whey is drained, resulting in loss of yield. Thus, the cut curds are initially left undisturbed for about fifteen minutes, and then are stirred gently.

Stirring continues as the curds are heated by raising the temperature in the jacketed vats. The temperature must be raised slowly at first (whether from 20°C or from 32°C) to prevent the curd exterior from cooking too fast and drying out.If this phenomenon, known as case-hardening, occurs, water molecules in the interior of the curd cannot escape and are held within the cheese. Ultimately, the curd-whey mixture is heated to about 52°C to 56°C, usually within one and a half hours (but according to some procedures, as long as three hours), with constant stirring.

Heating not only accelerates the rate of syneresis, the driving out of water from the curd, but temperatures above 45°C also arrest the fermentation. In fact, inactivating the culture at this step is the only way to keep the pH from decreasing too low. If the coagulated cheese is not cut until the pH has already reached 4.6 or below, then by the time the cook temperature is sufficiently high enough to inactivate the culture, the curds may already be too acidic. Cooking also inactivates coliforms and other heat-sensitive microorganisms (especially psychrotrophs, such as Pseudomonas).

After cooking has been completed, the whey is drained and cold (4°C) water is applied to the curds to quickly reduce the tem perature. The curd usually is washed two or three times. The water used for this washing step must be slightly acidic so that the precipitated casein is not re-solubilized.Also,the wash water is often chlorinated to ensure that spoilage microorganisms are not inadvertently added back to the curds.The water is drained, leaving behind what is called dry curd Cottage cheese. This product has a bland, acidic flavor (pH about 4.6 to 4.8), and contains mostly protein (20%) and water (nearly 80%). It is used mostly as an ingredient in lasagna, blintzes, and other prepared products. It is far more common to add a cream-based dressing to the dry curds, producing the familiar creamed Cottage cheese products of varying fat levels (generally ranging from 0% to 4%). The cream dressings typically contain gums and thickening agents, salt, emulsifiers, anti-mycotic preservatives (e.g., natamycin, sorbates, and other organic acids), and flavoring agents. Of the latter, di-acetyl distillates are frequently added to impart buttery-like flavor notes. Because the dressing contains lactose (which can be fermented), it is important that the starter culture bacteria be inactivated during the cooking step.

The packaged dry or creamed Cottage cheese is a perishable product and has a shelf-life of only two to three weeks under refrigeration conditions. However, the addition of new generation preservatives, such as Microgard, and the application of modified atmosphere (using CO2) and aseptic packaging, may increase shelf-life to as long as forty-five days. Cottage cheese is susceptible to spoilage for several reasons. The cheese vats are typically open (although most newer vats are enclosed), and exposure to air and environmental microorganisms can be significant. Because the final pH of creamed products can be as high as 5.4, and the water activity is also high (0.98 to 0.99), Pseudomonas and other psychrotrophic Gram negative bacteria can grow and produce fruity, rancid, and bitter off-flavors. Yeast and molds are the other main spoilage organisms, causing appearance as well as flavor and aroma defects. Flavor defects, such as high acidity and bitterness, are the result of excess growth by the starter culture. Other quality defects, including shattered, gummy, or soft curd, are usually caused by manufacturing flaws.

Manufacture of cream cheese (and its lower fat version, Neufchatel) is similar in principle to Cottage cheese, but the starting material, the manufacturing steps, and the finished product are quite different. First, cream cheese is made from pasteurized and homogenized milk containing as much as 12% fat. Most other cheeses are made using non-homogenized milk because homogenization results in a soft curd, which, in the case of cream cheese, is desirable. A mesophilic culture is added, followed by either a long or short set incubation.The acid-induced coagulum that forms at pH 4.7 is stirred (not cut) while the temperature is raised to as high as 73°C.The curds are then separated from the whey by special centrifuge-type devices or ultrafiltration systems. Although the resulting cheese material can be packaged as is, most cream cheese is mixed with other ingredients, including cream and gums, and then homogenized or mixed.The temperature is maintained above 72°C throughout the process. Packaging is done under aseptic conditions (i.e., in rooms under positive pressure with high efficiency air filtration systems in place), giving this product a long shelf-life (> 45 days).

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