Introduction

The hardest cheeses are the Italian Grana varieties and their industrial counterpart, Parmesan. The hard grainy texture of Italian Grana-type cheeses (e.g. Parmigiano-Reggiano or Grana Padano) results from the use of raw semi-skimmed milk for their manufacture and a high cooking temperature (-54 0C) [36] and evaporation of moisture during their long ripening period (often 2 years or more). Grana-type cheeses are sometimes consumed as a table cheese when they are young and relatively soft but the mature product is often used grated as a condiment on pasta or other dishes.

In addition to these traditional Italian cheeses with controlled designations of origin [82], Parmesan-type cheeses are made worldwide. Parmesan-type cheeses are often smaller than traditional Italian Grana-type varieties and are made from pasteurised milk and cooked to a lower temperature. They are more heavily salted, are ripened for shorter periods and often are made using exogenous lipases, which gives them a strong lipolysed flavour.

97 What causes the traditional grainy texture of Italian Grana-type cheeses?

M. Gobbetti

Parmigiano Reggiano and Grana Padano are known as 'Grana' cheeses because of the grainy texture of the ripened cheese. As indicated in the protocols of manufacture, the cheese structures of Parmigiano Reggiano and Grana Padano are defined as 'fine, brittle granules' and 'fine, grainy and radially fracturing into slivers', respectively.

Especially in the past, a limited role has been attributed to obligately heterofermentative lactic acid bacteria and gas-producing indigenous microorganisms which were considered responsible for the formation of micro-holes, just visible, owing to the synthesis of mainly CO2. Micro-holes may interfere with the grainy texture. Nevertheless, heterofermentative lactic acid bacteria (e.g. Lactobacillus fermentum) are contained in the natural whey starter [18] in a ratio of ca. 1:10 or higher with obligately homofermentative strains (e.g. Lactobacillus helveticus), and the milk currently used for the manufacture of the 'Grana' cheeses has a lower number of indigenous microorganisms than in the past.

The major cause of the grainy texture is associated with the technology of manufacture. Indeed, the grainy texture is associated with the use of semi-skimmed milk and extensive syneresis, which, in turn, is related to the size of the curd after cutting (dimensions of wheat grains, ca. 2-4 mm) and to the cooking temperature (54.5-56 0C), which are typical features of these extra-hard varieties of cheese [34, 35, 36]. During cooking, curd grains are stirred vigorously in moderately acidic (pH 6.2-6.3) whey. Under these conditions, curd grains undergo a very extensive syneresis. At the end of cooking, they become wrinkled, rough and very poorly cohesive; thus the curd grains tend to retain their individuality both on the bottom of the tank when they were pressed against each other and later in the mature cheese, which effectively determines its grainy texture.

The method of cutting a 'Grana' cheese is also important in maintaining its grainy texture. Considering the way by which a wheel of Parmigiano Reggiano cheese is cut in half before its sale, the most important factor is the particular and original tool used. It is a characteristic knife with a short, pointed and almond-shaped blade. One side is thinner to aid penetration while the other side is thicker because it must act as a wedge. Indeed, a wheel of 'Grana' cheese is not cut, but rather 'opened' so that its internal structure and its grainy texture are not altered.

Further reading

GOBBETTI, M. (2004). Extra-hard varieties, in Cheese: Chemistry, Physics and Microbiology Volume 2, 3rd edn, P.F. Fox, P.L.H. McSweeney, T.M. Cogan and T.P. Guinee (eds.), Elsevier Academic Press, Amsterdam, pp. 51-70. GOBBETTI, M. and DI CAGNO, R. (2002). Hard Italian cheeses, in Encyclopedia of Dairy Science, H. Roginski, P.F. Fox and J.W. Fuquay (eds.), Academic Press, London, pp. 378-385.

98 What common problems are associated with Grana-type cheeses?

M. Gobbetti and R. Di Cagno

The major problem associated with 'Grana' cheeses (Parmigiano Reggiano and Grana Padano) is gas production which is of microbiological origin due to the prolonged ripening (20-24 and 14-16 months, respectively) typical of these cheese varieties. Fermentation by clostridia [57, 91] and, occasionally, by propionic acid bacteria, may be the cause of late blowing.

During ripening spore-forming clostridia are responsible for the butyric acid fermentation usually starting from lactic acid as follows:

2CH3CHOHCOOH ^ CH3CH2CH2COOH + 2CO2 + 2H2

Three major species of clostridia have been found as agents of the late blowing due to the excessive production of CO2 and H2. Clostridium butyricum usually grows during the early ripening when lactose is still available as a carbon source and, especially, when the acidifying activity of lactic acid bacteria from the natural whey starter [18] is weak. Clostridium tyrobutyricum has the capacity to grow in 1-year-old cheese curd, especially when the pH becomes favourable owing to the utilisation of lactic acid and lactate as carbon source. Clostridium sporogenes grows after a year of ripening, it is very proteolytic and through the Stickland reaction uses free amino acids as carbon sources. When the butyric fermentation is intense, especially in the presence of Cl. sporogenes, off-flavours may be associated with late blowing. An example of late blowing by Cl. tyrobutyricum is shown in Fig. 1.

Butyric Fermentation Cheese
Fig. 1 Section of 'Grana' cheese: 'late blowing' caused by growth of Clostridium tyrobutyricum (from Bottazzi, 1993).

Propionic acid bacteria convert lactic acid into propionic acid, acetic acid, CO2 and H2O usually as follows:

3CH3CHOHCOOH ^ 2CH3CH2COOH + CH3COOH + CO2 + H2O

Propionic acid bacteria may grow only occasionally when the curd acidification has been weak and when the cheese has been salted to low levels.

Undesirable fermentations are usually prevented by several practices. The use of silage as fodder for cows is not allowed for the production of Parmigiano Reggiano cheese since it may be a vehicle for spore-forming bacteria, while the addition of lysozyme (2ghl—1) into the cheesemilk is allowed for the manufacture of Grana-Padano cheese as anti-clostridial agent, especially against Cl. tyrobutyricum. Overall, high hygiene at milking, the use of natural whey starters with high acidifying capacity and an appropriate, and rapid, salting are considered good practices to inhibit undesirable fermentations.

Other problems that may occur less frequently include: (i) poor gratability of 'Grana' cheeses due to a ratio of fat to caseins of >1 which is usual when skimming of cheesemilk is not optimal; (ii) off-flavours with a tendency to be bitter or very pronounced when the proteolytic activities of the natural whey starters are not correctly balanced and/or when the enzyme activities of the wild microflora prevail [91]; and (iii) excessive concentration of sulphur compounds (e.g. mercaptans), especially when microorganisms such as coryneform bacteria unusually prevail.

Further reading

BOTTAZZI, V. (1993). Microbiologia Lattiero-Casearia, Edagricole, Bologna. GOBBETTI, M. (2004). Extra-hard varieties, in Cheese: Chemistry, Physics and Microbiology Volume 2, 3rd edn, P.F. Fox, P.L.H. McSweeney, T.M. Cogan and T.P. Guinee (eds.), Elsevier Academic Press, Amsterdam, pp. 51-70.

99 How do traditional Italian Grana-type cheeses and industrial 'Parmesan' differ?

M. Gobbetti and R. Di Cagno

Parmigiano Reggiano and Grana Padano are 'Grana'-type extra-hard cheese varieties produced with Protected Designations of Origin (PDO) [82]. Unlike commercial trademarks, a PDO reflects a collective heritage and may be used by all producers of a particular variety in a defined geographical area. Protection derives its concept from using cheesemilk from a defined locality and applying technology under strict and traditional conditions which are not easily reproducible under a different geographical area. 'Grana'-type cheeses use cheesemilk produced from farms in a restricted area of the Pianura Padana, northern Italy. Milk from different areas is used for Parmigiano Reggiano and Grana Padano.

Feeding of the cows is carefully regulated. For the manufacture of Parmigiano Reggiano cheese feeding is subjected to the following restrictions: (i) the ratio between forage and other feeds must be > 1; (ii) >25% of the dry matter (DM) of the forage used must be produced on the same farm where the cheese is manufactured; (iii) >75% of the DM of the forage used must be produced within the district where the cheese is legally produced; and (iv) the feeding of silage is not allowed, to minimise the number of spore-forming, gas-producing bacteria in the feed [91]. Besides, raw milk is used for the manufacture of 'Grana'-type cheeses which are made by unique technology which respects artisanal protocols. The major features are: (i) the use of partially skimmed milk after overnight gravity creaming at ca. 20 0C in special tanks, 'bacinelle' (capacity 10-50 hl), which contain a shallow body of milk; (ii) the use of natural whey starter cultures [18] that contain strongly acidifying and synergistic thermophilic strains of lactic acid bacteria which are propagated following a typical procedure; (iii) the coagulation of milk in special copper tanks (ca. 10 hl) which have a peculiar shape and contain milk for the manufacture of two cheeses; (iv) the cooking of the curd grains to 54.5-56 0C which favour the typical grainy texture; and (v) the long time of ripening (12-16 months for Grana Padano and 18-24 months for Parmigiano Reggiano).

As recently stated by the Codex Alimentarius (July 2005), the term 'Parmesan' has just to indicate the English translation of the Italian Parmigiano Reggiano cheese. Indeed, 'Parmesan' cheeses, currently present in the market, are manufactured with: (i) milk produced from any farms which is subjected to skimming by centrifugation and to thermisation or pasteurisation; (ii) selected commercial cultures of lactic acid bacteria; and (iii) shorter time of ripening compared with the 'Grana'-type cheeses. In addition, industrial 'Parmesan'-type cheeses often have higher moisture than Italian Grana-type cheeses and may be manufactured using lipases to accelerate flavour development.

The above technological features are such that 'Grana' cheeses cannot be manufactured successfully under conditions which are different from those regulated by the protocols approved by the Consortia (http://www.parmigiano-

reggiano.it and http://www.granapadano.com) of Parmigiano Reggiano and Grana Padano cheeses.

Further reading

GOBBETTI, M. (2004). Extra-hard varieties, in Cheese: Chemistry, Physics and Microbiology Volume 2, 3d edn, P.F. Fox, P.L.H. McSweeney, T.M. Cogan and T.P. Guinee (eds.), Elsevier Academic Press, Amsterdam, pp. 51-70. GOBBETTI, M. and DI CAGNO, R. (2002). Hard Italian cheeses, in Encyclopedia of Dairy Science, H. Roginski, P.F. Fox and J.W. Fuquay (eds.), Academic Press, London, pp. 378-385.

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