Cheese-making Process
To give a general idea before start to give the details of the cheese production, it is possible to understand how the Mozzarella cheese is produced by the following video:
It is noticed that the cheese-making process has several steps. To emphasize the importance of each step, the flowcharts can be seen on the Figures 1 and 2. It will provide a better understanding about the process and will auxiliary the following detailed steps.
Fig 1. Cheese production Flowchart (1)
Fig 2. Cheese production (2)
Milk
The milk, raw material, can be from different species: cow, buffalo, sheep, goat, or it can be a mixture of milks from more than one species (3). Buffalo milk is known to be more appropriate than cow milk for Mozzarella cheese in view of its characteristic aroma, physical attributes and high income (4).
The type of milk (viz., cow, buffalo and their admixture) used for Mozzarella had a profound importance on the cheese composition. The cheese produced from a mixture of cow and buffalo milk can have high organoleptic quality and meltability comparing to those made from the individual milks; the nutritional value of buffalo cheese is superior as well (5).The meltability of ripened bovine and caprine milk cheeses are similar, when it is made from standardised milk. Bovine cheese has more free oil compared to caprine cheese (6).
Anyway, we chose the cow milk to produce the NutriSnack cheese for a convenience matter and easier to let it standardized.
Fig 3. Raw milk (7)
Preparation
The first technological phase is the straining of the milk over filters or sheets. This eliminates any unwanted particles that could be in the milk (3). The fat content, income, meltability and fat leakage of cheese increased with increasing milk fat levels, whereas moisture and protein content tended to decrease. pH and stretchability were not changed by the fat level in milk. (1). Mozzarella cheese made from 5.0% fat standardized milk was superior to those made from 0, 3.0 or 7.0% fat cow’s milk; the former had cholesterol content of 87.51 mg/100 g of cheese on 30th day of refrigerated storage (8).
- ACIDITY: The acidity must be held under control during all production steps, from the milking to the stretching. If the milk has the right degree of acidity it coagulates well: the acidity and the temperature of the milk are the factors that make difference on the renneting in its coagulation effect. If the curd does not reach the right degree of acidity during the maturation phase, it may then not be possible to stretch it; the proper acidity gives the chemical-structural alterations that are necessary for the whole stretching process. (3)
- HEAT TREATMENT: Pasteurization of milk is necessary for Mozzarella cheese that is consumed fresh, because the plasticizing process does not always destroy the all the pathogens (9). Heat treatment of milk (72°C, no hold) for Mozzarella cheese increases protein and Total Solids recovery but decreases the fat recovery, gives soft-bodied cheese and improves flavor score, keeping quality and ensured public health safety (10).
- HOMOGENIZATION: On one hand, milk homogenization (25 kg/cm2, 60°C) increases cheese moisture, Titratable Acidity, Total Volatile Fatty Acid and cohesiveness but, on the other hand, decreases stretchability, meltability, hardness, gumminess and chewiness. The flavour development is faster in cheeses prepared from homogenized milk (11).
Starter Cultures
Fig 4. Pasteurization of milk (12)
The mainly function of the starter culture is to produce acid in the fermentation process, they also help the cheese ripening step where their enzymes cause proteolysis and conversion of amino acids into flavour compounds (13). Starter bacteria can be defined as isolates which produce enough acid to reduce the pH of milk to <5.3 in 6 h at 30–37oC. Starter bacteria found most often are on the genera Lactococcus, Lactobacillus, Streptococcus, Leuconostoc and Enterococcus. (14) Direct-to-vat starters such as ‘Superstart’ are used where cooking temperature does not exceed 39.4°C. For those using starters composed of S. thermophilus and L. bulgaricus which are necessary when cooking at temperatures of ≥40°C, the popularity of the bacteriophage-inhibiting medium ‘Thermostar’ is advisable. (15)
Renneting
The milk is heated up to 36-38°C (this temperature favours the coagulating effect of the enzymes that are in the rennet) and the rennet is added (3). Several types of rennet i.e. of animal origin-Calf, bovine, porcine pepsin, of vegetable origin-Irpex lacteus and of microbial origin fungal rennet i.e., Meito, Marzyme and Surecurd have been used successfully to produce Mozzarella cheese (1).
Recovery of Total Solids of cheese decreases when using Mucor miehei rennet, while the recovery of protein and fat content in cheese are nearly the same. Mucor miehei rennet exhibited greater rise in Soluble Nitrogen content than other coagulants. Total Volatile Fatty Acid content increases with storage period and with increases fat content (1.5 vs. 3.0%) of the milk. The coagulant types do not affect the Soluble Nitrogen or Total Volatile Fatty Acid. The type of coagulant had negligible effect on meltability, fat leakage and oiling-off of cheese. Mozzarella cheese made with Mucor miehei had the highest firmness. Mucor miehei rennet exhibited highest rate of proteolysis during storage and such cheeses are preferred over cheese made by other two coagulants (16).
**Pasteurized milk is incubated at 33°C with rennet and a starter culture including of lactobacilli and streptococci is used. The separated curd (pH 5.2) is heated in water at 80°C, molded and formed into 150-250 g balls which are chilled in running water at 10-12°C for 30 min followed by immersion (5°C) brine for 30 min (17).**
Fig 5. Renneting of the milk (18)
Studying the cheese making process we could conclude that the bioreactor has to have a pH 5.2, working in a temperature of 33oC in 30 to 40 minutes. With this, the bioreactor has to content pressure valve, control parameters, cooling jacket, cooling system, whey removal and exhaust. It has to have an entrance to the starting material, a pressure valve, control of the parameters pH, pressure and temperature, a cooling jacket, a cooling system, an exit for the whey removal and an exhaust, as can be seen in the Figure 6.
Cutting
Figure 6. Bioreactor for cheese production.
The cutting expels the whey from the curd. The coagulation has transformed the milk (liquid state) into curd (gel state); more specifically, the curd contains whey - a liquid made up of water, lactose and proteins. Depending on the kind of cheese that we want to produce, the cutting can be of two different types. If we want to make soft cheese (like buffalo Mozzarella cheese) the cutting process must be divided in two phases separated by a more or less long lapse of time: in the first phase the curd is cut into big cubes using a knife; during the following pause can be noticed the separation between whey and curd. During the second cutting (with a curd knife) the cubes are reduced into nut-size granules, soft and very moist because of the whey, that will give birth to a soft cheese. Instead, only one cutting will be necessary (always with a curd knife) if we want to produce a hard cheese; in this case the cutting takes longer and finishes when the curd has been transformed in corn- or rice-sized granules: very small granules that do not contain much whey, therefore hard, permitting to give birth to a hard cheese.
In the specific case of buffalo Mozzarella cheese, the curd is cut during two phases: with the first cutting the curd is cut in cubes with a knife; after about 5 minutes takes place the second cutting, that reduces the curd into nut-size granules (3-6 cm) with a curd knife. This phase is very important for the buffalo Mozzarella cheese’s composition and its final production yield. For example, during the cutting some fat is always lost into the whey (i.e., part of the fat passes from the curd to the whey; there can be up to 1% of loss). A good cutting is thus fundamental to reduce these losses: it is best to always stir the curd gently. (3)
Acidification
Fig 7. Cutting of the cheese (19)
Direct Acidification technique has gained considerable commercial interest, as it does not depend on starter performance (unpredictable, risk of phage infection, milk contaminated with antibiotics) and helps the mechanization of production (20). The different types of acids employed in this technique include hydrochloric acid, phosphoric acid, lactic acid, acetic acid, malic, citric acid and glucono-delta-lactone (1). Mozzarella cheese prepared by Direct Acidification, with or without added microorganisms have a quicker yield method of reaching the required pH value for stretching. (21)
Equipments
The mechanization in the manufacture of Mozzarella cheese includes the development of machines to form and shape cheese balls, moulding, automatic plasticizing and stretching of curd, salting, automatic moulder-cooling, moulding and hardening, cheese compacting, automatic brining and chilling of cheese and shredding (1).
Mechanical mixers with single screw or twin screws, in conjunction with steam injection have been used for heating and stretching the cheese. Typically, the water temperature used in cooker-stretcher ranges from 60-85°C and the cheese temperature as it exits the mixer ranges from 50-65°C (22).
- Continuous production lines in mozzarella cheese manufacture: The process mainly involves use of continuous mixing, cooking, drawing, plasticizing, moulding, salting/brining and packaging machines. Studies have shown the utility of linear programming in the allocation of milk resources for Mozzarella cheese making to maximize net returns and cheese yield or minimize cost. (23)
Slicing and Spraying
Various empirical techniques using low-temperature dynamic rheological analysis (24) have been utilised to evaluate process cheese hardness, factorability, cohesiveness, adhesiveness, gumminess, chewiness, slicing ability, and elastic and viscous properties at low temperatures. Moreover, different process cheese manufacturers throughout the United States employ various customised techniques to measure the unmelted texture of process cheese such as firmness, slicing ability, and stickiness/adhesiveness depending on the resources available at their facilities. (25)
Studies have shown that feta cheese samples sprayed with different concentrations of oregano essential oil showed antibacterial activities against Listeria monocytogenes and Escherichia coli O157:H7 (26). Experiments in vitro showed the effectiveness of the antibacterial activities of three different concentrations (1, 2, 5%) of oregano essential oil against Bacillus cereus, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Salmonella Typhimurium. Just Pseudomonas aeruginosa showed resistance to all concentrations of employed essential oil. However, for all of the other strains, the essential oil was effective - 5 percent most effective (27).
References
(1) Jana, A. H., & Mandal, P. K. (2011). Manufacturing and quality of Mozzarella cheese: A review. International Journal of Dairy Science, 6(4), 199-226.
(2) https://www.britannica.com/topic/dairy-product/images-videos
(3) http://www.fao.org/ag/againfo/themes/documents/milk/mozzarella.pdf
(4) El-Koussy, L. A., Mustafa, M. B. M., Abdel-Kader, Y. I., & El-Zoghby, A. S. (1995). Properties of Mozzarella cheese as affected by milk type, yield recovery of milk constituents and chemical composition of cheese. In Proceedings of the 6th Egyptian Conference for Dairy Science and Technology (DST’95), Egypt (pp. 121-132).
(5) Sameen, A., Anjum, F. M., Huma, N., & Nawaz, H. (2008). Quality evaluation of Mozzarella cheese from different milk sources. Pakistan Journal of Nutrition, 7(6), 753-756.
(6) Imm, J. Y., Oh, E. J., Han, K. S., Oh, S., Park, Y. W., & Kim, S. H. (2003). Functionality and physico-chemical characteristics of bovine and caprine mozzarella cheeses during refrigerated storage. Journal of Dairy science, 86(9), 2790-2798.
(8) Ali, A. M., & Abdel-Razig, K. A. (2011). Cholesterol content of mozzarella cheese during storage as affected by level of milk fat. Pakistan Journal of Nutrition, 10(1), 65-70.
(9) Caserio, G., Senesi, E., Forlani, M., & Emaldi, G. (1977). Hygienic quality of mozzarella cheese in relation to manufacturing technology. Latte, 8, 706-721.
(10) Patel, G. C., Vyas, S. H., & Upadhyay, K. G. (1986). Evaluation of Mozzarella cheese made from buffalo milk using direct acidification technique. Indian journal of dairy science, 39, 394-403
(11) El-Batawy, M. A., Galal, E. A., Morsy, M. A., & Abbas, K. A. (2004). Utilization of ultrafiltration technique in making Mozzarella cheese from different kinds of milk. Egyptian J. Dairy Sci, 32, 303-314.
(12) http://site.shbenyou.com/milk-production-line.html
(13) Fox, P. F., & Wallace, J. M. (1997). Formation of flavor compounds in cheese. Advances in applied microbiology, 45, 17-86.
(14) Beresford, T. P., Fitzsimons, N. A., Brennan, N. L., & Cogan, T. M. (2001). Recent advances in cheese microbiology. International Dairy Journal, 11(4), 259-274.
(15) Ferris, S. (1981). Italian cheese--the US experience and future trends. Dairy industries international, 46, 17-22.
(16) Ahmed, N. S., El-Gawad, M. A. A., El-Abd, M. M., & Abd-Rabou, N. S. (2011). Properties of buffalo Mozzarella cheese as affected by type of coagulante. Acta Scientiarum Polonorum. Technologia Alimentaria, 10(3), 339-357.
(17) Weckx, M., & Delbeke, R. (1971). The manufacture of Mozzarella and Pizza cheese. J. Agric, 24, 1327-1349.
(18) http://www.wisegeek.org/what-is-rennet.htm#didyouknowout
(19) http://www.pennmac.com/blog/2011/11/how-is-cheese-made/
(20) Fox, P. F. (1978). Direct acidification of dairy products. Dairy Science Abstracts (UK).
(21) Wood, R. (1987). Italian cheese making: A fascinating process. Milk Ind., 89, 10-13.
(22) Renda, A., Barbano, D. M., Yun, J., Kindstedt, P.S. and Mulvaney, S. J. (1997). Influence of screw speeds of the mixer at low temperature on characteristics of Mozzarella cheese. Journal of Dairy Science, 80, 1901-1907
(23) Kerrigan, G. L., & Norback, J. P. (1986). Linear programming in the allocation of milk resources for cheese making. Journal of Dairy Science, 69(5), 1432-1440.
(24) Drake, M. A., Gerard, P. D., Truong, V. D., & Daubert, C. R. (1999). Relationship between instrumental and sensory measurements of cheese texture. Journal of Texture Studies, 30(4), 451-476.
(25) Kapoor, R., & Metzger, L. E. (2008). Process cheese: Scientific and technological aspects—A review. Comprehensive Reviews in Food Science and Food Safety, 7(2), 194-214.
(26) Govaris, A., Botsoglou, E., Sergelidis, D., & Chatzopoulou, P. S. (2011). Antibacterial activity of oregano and thyme essential oils against Listeria monocytogenes and Escherichia coli O157: H7 in feta cheese packaged under modified atmosphere. LWT-Food Science and Technology, 44(4), 1240-1244.
(27) Cattelan, M. G., Castilhos, M. B. M., Sales, P. J. P., & Hoffmann, F. L. (2013). Antibacterial activity of oregano essential oil against foodborne pathogens. Nutrition & Food Science, 43(2), 169-174.