Lynn+Dao

=**Introduction**= A food that is produced into a myriad of varieties throughout the world, both historically and geographically, is cheese. Generally, cheese is used in hundreds of different cultures’ cuisines, as condiments, appetizers, snacks, entrees, and even deserts. The production of this dairy marvel, the earliest record of which dates back to 5,500 B.C. [1], involves a series of chemical processes. Depending on the type of desired cheese produced, some processes and ingredients are added, removed, or modified. Figure 1 shows the general process flow of how most cheeses are produced [2].

//Figure 1: General Process for Making Most Cheeses//

=**Preparation**= The primary ingredients used in cheese production are milk, a coagulant, flavoring, and bacterial cultures. The most common types of milk used are goat, cow, sheep, buffalo, or a combination of these milks [3]. More acidic cheeses require “an acid source such as acetic acid or gluconodelta-lactone,” whereas rennet (derived from animal stomachs, fungus, or plant) cheeses require calcium chloride “to improve the coagulation properties of the milk” [4, 5].

Cheeses of different flavors, colors, and textures require different additional natural and artificial ingredients on top of the manufacturing process, including but not limited to spices, herbs, condiments, and seasonings. For example, pepper jack cheese is favored with jalapeño peppers for the spiciness and cream cheese is thickened with carob bean gum [6]. Lastly, the most common bacterial culture used for cheese processing is lactic acid bacteria (LAB) fermentation. According to Briggiler-Marco, “cheese-making is based on application of LAB in the form of defined or undefined starter cultures that are expected to cause a rapid acidification of milk through the production of lactic acid, with the consequent decrease in pH, thus affecting a number of aspects of the cheese manufacturing process and ultimately cheese composition and quality” [2]. After the four primary ingredients are gathered, the following processes determine the type of cheese produced.

=Milk Treatment= It is necessary to treat the milk first, which is usually achieved via heat treatments, including “thermisation (65°C, few seconds), low pasteurization (72°C, 15 seconds), high pasteurization (85°, 20 seconds, and ultra high temperature treatment (e.g. 1 second, 145°C)” [7]. Pasteurization is a thermal process by which food is decontaminated and “is still in common use today, for being efficient, environmentally friendly, preservative-free and inexpensive when compared to other preservation technologies” [8]. Cheeses made from raw (unpasteurized) milk are required by the FDA to be maintained at a temperature of at least 1.7°C for at least 60 days, assuming that the microorganisms “would eventually die in the low pH, low water activity, high salt, competitive cheese environment” [9]. Finally, the milk is cooled after pasteurization (raw milk is heated) to 32°C to prepare for the addition of the bacterial culture, so that it can grow [4].

=Coagulation= After the milk is treated and reaches the right temperature, it is poured into a cheese vat and “inoculated with the lactic acid-producing bacteria”, which lowers the pH and sours the mixture [10]. Rennet cheeses require the addition of rennet of which the enzymes decrease the required activation energy for the reaction, meaning that the enzymes “selectively work on specific amino acid sites that make up proteins in milk” [11]. Milk contains caseins – a group of four main phosphoproteins (α-s1, α-s2, β, κ). Figure 2 illustrates the basics of the structure to identify how the caseins differentiate from each other. The molecular structure of the caseins is defined as calcium salt micelles (organized formed in a liquid of amphiphilic macromolecules) enclosed in κ-casein and is heat-stable during pasteurization [12, 13]. The enzymes break down the caseins and make them bond and forms curds.

//Figure 2: The general structure of the casein//

In the rennet cheeses, different rennet sources contain different enzymes that cleave the caseins selectively. Animal rennet contains chymosin and pepsin that slowly break up the α-caseins that “release smaller peptides...free to form complex aroma[s].” Plant rennet enzymes release peptides that possess bitterness. Microbial rennet cleaves the κ-caseins via hydrolysis, which is ideal for fresh cheeses or cheeses that are “inactivated by heat,” but also releases bitter peptides. Fungal rennet with chymosin is a cheaper alternative to animal rennet, and therefore, is the most used source today [11].

Coagulation takes approximately 35 minutes around 30°C after the addition of the enzymatic cultures and rennet, a small temperature fluctuation of -2°C from the temperature at which the milk treatment ended [14]. During this time, the mixture is left undisturbed for the solid curds to formulate and reach pH 6.4 [4]. The curd behaves similar to a sponge, absorbing and releasing the water and whey proteins in the vat. The curd is cut for about 10 minutes “into smaller pieces, increasing the surface area of the curd and allowing it to expel water and whey more effectively.” Typically, the curd goes through four series of cuts – first “along the length” of the vat, second “perpendicular to the first cuts,” third at “another angle,” and fourth on the edge to separate the curd from the walls [15]. Knives, such as the patented curd cutting apparatus in Figure 3, are used. The curds vary in size and density that ultimately affect the texture and flavor of the final cheese.

//Figure 3: Curd Cutting Apparatus [15]//

Following the curd cut, the mixture is heated to 40°C for approximately 90 minutes, promoting separation of the whey and curd. The mixture is also stirred for the first 30 minutes of heating. The mixture is allowed to settle after heating, after which whey draining will occur.

=Whey Draining & Salting/Pressing= After the whey and curd have been separated via coagulation, the whey is removed from the vat. Figure 4 illustrates a general, basic way of filtering out the whey fluid from the solid curd. The whey flows through a screen to catch any “curd dust” [10]. Since the curd expels much moisture, the particles may bond together and the curd becomes more compactly dense. The removed whey may be used to make other cheese-like products. The amount of whey removed depend on the desired texture of the final cheese product. The harder the cheese, the more whey is removed from the curd.

//Figure 4: Liquid whey separated and filtered of solid curd [2]//

At this step in the process, the texture and flavor of the cheese may be manipulated. For example, cheddar cheese undergoes a process (appropriately) called “cheddaring”. During this process, the curd is allowed to “mat” together where the small particles come together and bind to become more compact [16]. The acidity (lactic acid) is between 0.45% – 0.6% and the acid “combines with the calcium paracaseinates of the curd and converts these compounds into forms containing less calcium” [17]. Paracaseinates are the compounds created by the rennet enzymes acting on the κ-casein [18]. Once the desired texture is reached, the curd is cut into slabs and then piled on top of one another. The weight of the piles promote further whey removal from the bottom slabs, analogous to pressing down on a sponge. This process is continuously repeated so that the slabs are evenly pressed and that the density and texture are consistent for the whole batch [16].

For cheeses in general, after the desired texture is achieved, the curd is milled or “broken up into small pieces enabling it to be salted evenly” [2]. The salt, usually in brine for even distribution or in solid form for sprinkling, aids both taste and preservation. The cheese is then pressed into blocks. Upon completion of the salting and block forming is the ripening phase, which is the last step in the cheese-making process.

=**Ripening**= Finally, the final step in a general cheese-making process is the ripening stage. It is usually the longest step – the age ranging from 2 weeks to several years, during which the flavor of the cheese is truly developed. The lactic acid bacteria enzymes break down the protein in the cheese to peptides and amino acids, or proteolysis [2]. This is also the most complex series of chemical reactions in making cheese. Figure 5 shows the process flow of proteolysis.

//Figure 5: Proteolysis Flow Diagram//

This series is catalyzed by a myriad of enzymes sources in the cheese, such as the coagulant, milk, starter, non-starter, or secondary cultures, and externally added enzymes for accelerating the process. The flavors are developed during the biochemical changes during ripening and are “an important organoleptic attribute and the correct balance of sapid compounds” [19]. Although the amino acid ratios are important in flavor development, it is difficult to correlate the concentration of certain amino acids to the ripening speed or to the flavor intensity. Cheese would normally be stored in a facility on shelves.. However, the longer the cheese ages, the sharper the taste due to the acid increase [20]. It is crucial to have control over facility parameters (e.g. humidity, temperature) to ensure successful ripening [2].

=Conclusions= The cheese-making process follows a simple series of general steps, but the chemistry involved may get complex. People have been making cheese since before recorded history, and is still being manipulated today to make countless different types of cheese. Because of the limitless ways to produce cheese, much research is still being conducted to try to characterize qualitatively and quantitatively the effects of certain components or steps in the process on characteristics of the cheese.

=References= [1] N. Subbaraman, "Art of cheese-making is 7,500 years old" Nature.com. Nature Publishing Group, 12 Dec. 2012. Web. <[|DOI] >. [2] J. Marcelino Kongo (2013). Lactic Acid Bacteria as Starter-Cultures for Cheese Processing: Past, Present and Future Developments, Lactic Acid Bacteria - R & D for Food, Health and Livestock Purposes, Dr. J. Marcelino Kongo (Ed.), ISBN: 978-953-51-0955-6, InTech, <[|DOI] >. [3] E. Rahimi, Lead and cadmium concentrations in goat, cow, sheep, and buffalo milks from different regions of Iran, Food Chemistry, Volume 136, Issue 2, 15 January 2013, Pages 389-391, ISSN 0308-8146, <[|DOI] >. [4] "Milk Facts." Cheese Production. The Milk Quality Improvement Program, Department of Food Science, College of Agriculture and Life Sciences, Cornell University. Milk Facts, n.d. Web. <[|http://www.milkfacts.info/Milk Processing/Cheese Production.htm] >. [5] B. Galivan. "Cheese 101: What Is Rennet?" Examiner.com. Clarity Digital Group LLC, 26 Dec. 2010. Web. <[] >. [6] K. Horan, C. Galer, P. Gass, A. Handrick, J. Hirshey, B. LeVine, D. Reddy, C. Trinka. CHEESE WITH ENHANCED ORGANOLEPTIC AND MELTING PROPERTIES. U.S. 2013/0052325A1. 28 February 2013. < > [7] D. Jong, METHOD AND APPARATUS FOR USE IN MAKING CHEESE. W.O. 2010/137983A1. 2 December 2010. < > [8] Filipa V.M. Silva, Paul A. Gibbs, Thermal pasteurization requirements for the inactivation of Salmonella in foods, Food Research International, Volume 45, Issue 2, March 2012, Pages 695-699, ISSN 0963-9969. <[|DOI] >. [9] J.C. Brooks, B. Martinez, J. Stratton, A. Bianchini, R. Krokstrom, R. Hutkins, Survey of raw milk cheeses for microbiological quality and prevalence of foodborne pathogens, Food Microbiology, Volume 31, Issue 2, September 2012, Pages 154-158, ISSN 0740-0020, <[|DOI] >. [10] G. Reinbold, M. Reddy. METHOD OF MANUFACTURING CHEESE FROM STARTER CULTURES. C.A. 1178113. < > [11] Pav. "Understanding Coagulants." Washington Cheese Guild. N.p., 19 July 2010. Web. <[] >. [12] "General Properties of Casein | Sigma-Aldrich." Sigma-Aldrich. N.p., n.d. Web. <[] >. [13] M. Vert, Y. Doi, K. Hellwich, M. Hess, P. Hodge, P. Kubisa, M. Rinaudo, F. Schue. Terminology for biorelated polymers and applications (IUPAC Recommendations 2012). IUPAC. 11 January 2012. < [|DOI] >. [14] F. Rattray, A. Johansen, M. Broe. “Method for Making Cheese” WO 2010/022790A1. 4 March 2010 < > [15] D. Oakley. “Curd Cutting Apparatus” US 2011/0239873A1. 6 October 2011. < > [16] J. Stine. “Manufacture of American type Cheese” US 2,494,638. 17 January 1950. < > [17] “Improvements in or relating to the preparation of curd for the manufacture of pasteurized cheese, the preparation of pasteurized cheese, and the curd and pasteurized cheese resulting therefrom” US 473,833. 13 October 1937. < > [18] “Annual Report of the Department of Agriculture”. New York Agriculture Experiment Station. Geneva, Ontario County. p. 288. 15 January 1914. <[|ZIP LINK] > [19] M.J Sousa, Y Ardö, P.L.H McSweeney, Advances in the study of proteolysis during cheese ripening, International Dairy Journal, Volume 11, Issues 4–7, 11 July 2001, Pages 327-345, ISSN 0958-6946, <[|DOI] >. [20] "Matting and Cheddaring - Dairy." Matting and Cheddaring - Dairy. Army Medical, n.d. Web. <[] >.

BACKUP - If the zip links to the references above do not work, they may also be found in this zip file link, which is password protected. Please download the zip file and then enter the password given in class. [|ZIP REFERENCES]

Attached in the link below is the multimedia accompaniment to this research paper in a video format. [|VIDEO LINK]

If the video link does not work, please download the powerpoint from this link and "view slide show" to ensure the audio is enabled with the slides. [|POWERPOINT FILE] [|VIDEO REFERENCES]