BLUE COLORATION IN CHEESE 117 



attributed to blue milk by early observers Steinhof and Mosler have been 

 controverted by Haubner ; therefore, if illness has actually ensued on the con- 

 sumption of such milk, the fission fungus in question was not to blame. Harm- 

 lessness apart, blue milk is not a merchantable article, and its sale should be 

 prohibited, since its appearance is, to put it mildly, unappetising. 



Since the causes of this blue coloration in milk have become known, its 

 occurrence has, as a rule, been very limited ; and when it is observed, many ways 

 of combating it are employed, chief among them being scrupulous cleanliness in 

 all appliances and utensils with which the milk comes into contact. The dairy 

 or milk-room is then thoroughly sulphured several times, and, finally, a little 

 salt or Glauber salt (sodium sulphate) is added to the cows' dietary. This last- 

 named remedy must, however, be employed with discretion, since, under certain 

 circumstances, it may prejudicially affect the health of the animals and the 

 composition of the milk, as was ascertained by E. HESS, F. SCHAFFER, and 

 M. LANG (I.). The milkers' hands and the cows' udders should be carefully 

 washed before milking. The sudden appearance of the evil, and its frequent 

 disappearance after a change of fodder, permit the conclusion that the bacillus 

 occurs not infrequently on ceitain vegetables, from which it finds its way into 

 the dung of the animal and thence into the milk. 



As has already been stated, the blue coloration of milk by bacterial agency is 

 effected gradually when the liquid is left to stand, and first makes its appearance 

 on the surface. If, on the other hand, the milk is of a bluish or blue colour 

 when freshly drawn, this results from the cow having partaken freely of the 

 flowering rush (Eutomus umbellatus), which contains a blue colouring matter 

 (indigotin ?) that is taken up by the gastric juices, conveyed in an unaltered 

 condition into the arterial circulation, and thus finds its way into the milk. 



95. Blue Coloration in Cheese. 



This is an evil to which the Dutch dairy industry is particularly liable. 

 Since it very often makes its appearance only after the ripening stage is over 

 that is to say, at a time when the article has already passed into the hands of the 

 salesman it is the cau^e not only of monetary loss to the cheese-maker, but 

 also of unwelcome complaints on the part of the purchaser. The phenomenon 

 manifests itself in various forms. Either the whole bulk of the cheese is of a 

 bluish cast, or exhibits blue patches internally, or, finally, is interspersed with 

 blue spots (Dutch, "stipjes") from i to 2 mm. (^ to -^ inch) in diameter, the 

 latter form (blue grain : Dutch, " blauwstippigkeit ") being the most common. 



The causes of blue cheese are twofold ; one of them being chemical, and due 

 to iron sulphide, as was demonstrated by M. SCHMOEGER (I.) and TH. KLARVER- 

 WEIDEN (I.). Normal cheese contains but a very small quantity of iron ; Cheddar, 

 for instance, having 0.009 P er cen ^. ; Gouda, o.on per cent., and so on. If, 

 however, a larger quantity of iron obtains admittance to the milk or freshly 

 precipitated curd, it will then gradually, during the ripening process, enter into 

 combination with the sulphuretted hydrogen separated from the albumen by 

 bacterial action, aud will form iron sulphide, which, as is well known, exhibits a 

 blue shade when in a dilute condition. When the iron has been admitted in 

 the soluble form, then cheeses coloured a fairly uniform blue or bluish shade 

 throughout will result. If, on the other hand, the metal be present in coarser 

 particles, e.g. in the form of rust, then a patchy-blue or blue-grained cheese will 

 be obtained. This explains the more frequent occurrence of the phenomenon 

 since the introduction of the centrifugal machine into the dairy industry, the 

 numerous rivets of the iron cylinder of this machine being, as demonstrated by 

 Schmoeger, so many sources of contamination of the milk by rust. Careful 



