August, 1938 Research Bulletin 237 Bacteriology of Cheese III. Some Factors Affecting the Ripening of Blue · (Roquefort Type ) Cheese ~y C. B. LANE AND B. W. HAMMER AGRICULTURAL EXPERIMENT STATION IOWA STATE COLLEGE OF AGRICULTURE AND MECHANIC ARTS R. E. BUCHANAN. Director DAIRY INDUSTRY SECTION AMES, IOWA CONTENTS Summary .............................. _...................................................................... _.... 197 Historical ..................................................................................................... __ ... 202 Manufacture of blue· veined cheeses.................................................. 202 General types of organisms involved in the ripening of blue· veined cheeses ............................................................................... __... 202 The penicillia important in ripening blue·veined cheescs .............. 203 General action of the penicillia .................................................... _... 204 Flavor in blue·veined cheeses .. __ ................................................... _.. _... 205 Common defects of blue· veined cheeses ....................................... __ ... 206 Preparation of mold powders for blue·veined cheeses_ ............... _... 207 Methods ....... ~ .................................................., ............................ _................ _.. 207 Manufacture of cheese ........................... _.......................................... _... 207 Source and treatment of milk. .. __ ................................................. _... 207 General manufacturing procedure ........................... _.................. _... 207 Preparation of mold powder.. ..... _........................................................ 209 Examination and scoring of cheese ................................................ _... 209 Chemical analysis of cheese_ ................................................ _................ 209 Total _volatile acidity....................... _................................................. 209 General types of volatile acids ....................................... _............ _... 209 Nitrogenous decomposition in cheese ................. _................. ......... 210 Acid value of faL .............................. _._ ........................................ _... 210 Results obtained....................... _................................................... ................... 210 Inoculation of curd with mold powder. .................. _..................... __ ... 210 Effect of amount of mold powder used .................................... _... 210 Addition of mold powder to curd before hooping_ ....................... 211 Effect of the strain of mold used ............................................... _........ 212 Manufacture of blue cheese from homogenized mil~ .................. 220 Development of the method........ __ .............................. _..................... 220 General effect of homogenization ............................................... _.... 221 Commercial lots of cheese ................................................................ 223 Effect of the homogenization temperature ... _............... .......... _...... 224 Effect of the homogenization pressure......................... _............ ___ . 225 Effect of homogenization on the volatile acid developmenL. __ . 225 Effect of pasteuring and then homogenizing the miIL ______________ 226 Comparison of cows' milk and goats' milk for blue cheese ______ 230 Effect of delayed salting____________________________________________________________________ 231 General action of milk lipase in ripening cheese _______________________ . 232 Effect of delayed hooping __ . _________ . _______________________________ .:_________________ __ . 234 Effect of not skewering the cheese ________________________________________ __________ 235 Small units of cheese ________________________________________________________________________ 236 Literature cited 237 . SUMMARY Blue cheese was manufactured by several methods. The cheese was studied organoleptically and sometimes chemically during the ripening to determine the effects of the various manufacuring pro· cedures. The results obtained are as follows: 1. A very small amount of mold powder (0.01 percent of the weight of curd) was sufficient to produce satisfactory mold growth in blue cheese. 2. The method of mIXmg mold powder with the curd before hooping, rather than dusting the powder on layers of curd in the hoops, appeared to have certain advantages from the standpoints of mold distribution and general appearance of the ripened cheese. 3. In comparisons of eight strains of penicillia for the ripening of blue cheese, the strains showed rather consistent variations in the amounts of volatile acid produced in cheese, the acid value of the cheese fat and the extent of nitrogenous decomposition. Certain strains gave cheese having a desirable flavor and luxuriant mold growth, while other strains gave cheese having undesirable flavors and poor mold growth. In general, cheese containing comparatively large amounts of volatile acid and having relatively high fat acidi· ties had considerable of the sharp, peppery flavor characteristic of blue cheese, whereas cheese containing comparatively small amounts of volatile acid and having relatively low fat acidities were usually lacking in flavor. 4. The manufacture of blue cheese from homogenized milk by the method described, rather than from milk not homogenized, offers certain possibilities from the standpoints of curing and marketing. In general, cheese made from homogenized milk ripened in a rela­ tively short period, was comparatively light in color and the body was unusually soft so that the cheese could be easily spread with a knife. The cheese from various lots was also rather uniform in quality. On the other hand, cheese made from milk not homo­ genized required extended ripening before a desirable flavor was apparent and often developed flavor defects; in addition, the body was comparatively hard, and the color was yellow. 5. Commercial lots of cheese made from homogenized milk were of good quality and had considerable flavor after 10 to 14 weeks of ripening. 6. Comparisons of three temperatures [7soF. (23.9°C.), 9soF. (3S.0°C) and l1soF. (46.1 0C.) ] for the homogenization of milk intended for blue cheese under 2,SOO +SOO pounds pressure, indi­ cated that 9So F. was the most desirable temperature from the stand­ point of a comparatively rapid flavor development in the cheese. When large lots of milk were homogenized, 90 ° F. (32.2°C.) was commonly used with good results. 7. Comparisons of three pressures (2,000 + SOO, 3,000 + soo and 4,000 +SOO pounds) for the ~omogenization of milk intended for blue cheese when the temperature was 9soF. (3S.0°C.) indic"ated that 3,000 +SOO pounds was the most generally satisfactory, al­ though 2,000 + SOO also gave good results. With large lots of milk a pressure of 2,SOO + SOO pounds was commonly used. 8. The values obtained for volatile acidity on cheese made frQm homogenized milk were roughly two to four times as high as the values obtained on cheese made from milk not homogenized. 9. In general" cheese made from pasteurized homogenized milk showed a more rapid development of volatile acid, higher acid val­ ues on the fat and a more typical flavor than cheese made from raw milk not homogenized. However, it did not ripen as rapidly as cheese made from raw homogenized milk. 10. Comparisons of cheese made from (a) cows' 'milk not homo· genized, (b) homogenized cows' milk, (c) goats' milk not homo· genized and (d) homogenized goats' milk, indicated that the cheese made from homogenized cows' milk was the most generally satis­ factory. 11. Delaying the salting of cheese made from homogenized milk until 2 to 8 days after skewering did not appear to be a desirable practice from the standpoint of the color; cheese held for 8 days before salting was decidedly yellow. 12. In comparisons of cheese made from raw and pasteurized skimmilk to which butter, boiled cream or raw cream had been added in amounts -necessary to make the fat content comparable with whole milk and the mixtures then homogenized, the cheese made from raw skimmilk plus the fat ingredients quickly developed ran­ cidity ~nd the flavor and aroma of methyl-n-amyl ketone, while no early rancidity or ketone flavor and aroma developed in the cheese made from pasteurized skimmilk plus the fat ingredients. These results suggest that the milk lipase definitely aids in the cheese ripening. 13. Delaying the hooping of the curd was not a desirable pro· cedure in the manufacture of blue cheese since the cheese shattered readily, and although a sharp, peppery flavor developed very early it was not typical or altogether desirable. 14. Un skewered cheese made from homogenized milk developed considerable flavor after a few months of ripening although this fla­ vor appeared to be due primarily to the formation of comparatively large amounts of methyl-n-amyl ketone. When unskewered cheese was made without the addition of mold powder to the curd, no ke­ tone flavor developed; the ketone flavor was more noticeable in the cheese made with relatively large amounts of powder than in that made with small amounts. Un skewered cheese made from homo­ genized milk regularly had a hard, coarse body even after consid­ erable ripening. When a culture of Lactobacillus casei or Strepto­ coccus liquefaciens was added to the milk used for cheese making, the cheese