DAIRY. 



551 



tiairy. From the above table it appears, that curd of a good 



""~^_ ■" quality may be obtained from milk heated from 87 to 

 103 degrees of Fahrenheit, provided, as Mr Marshall 

 observes, the rennet be so proportioned, that the time of 

 coagulation be from three quarters of an hour to two 

 hours and a half; and provided the milk be kept pro- 

 perly covered during the process of coagulation. "Frcm 

 these," continues he, " as well as from a variety of 

 other observations which I made in the course of the 

 summer, it appears to me, at present, that frcm 85 to 

 5)0 are tlie proper degrees of heat ; ;;nd that from one to 

 two hours is the proper time of coagulation ; and that 

 the milk ought to be covered, so as to lose, in the pro- 

 cess, about five degrees of its original heat. Still, how- 

 ever, he confesses, that his observations and experi- 

 ments have not been extensive enough to furnish a suf- 

 ficient illustration of this very difficult subject. " Cli- 

 mate, season, weather, and pasture," he says, " may 

 require that these bounds should sometimes be bro- 

 ken." 



It would appear, from the experiments of the 7th, 8th, 

 and 9th of June, that the quality of the curd arises as 

 much, perhaps, from the heat of the milk when it 

 comes, as from its heat when set ; for the whey on the 

 9th was 4 degrees higher than that on the Sth, though 

 the milk had been set to steep two degrees lower. Per- 

 haps, too, a great deal depends on the curd being bro- 

 ken up at the critical minute, and not allowed to stand 

 after it has come. 



Mr Marshall, however, at a later period, viz. in 

 1788 (see his Rural Economy of Gloucestershire), tells 

 us, that the following observations were accurately 

 made by him ; and the results, it must be confessed, 

 vary considerably from those already stated ; an addi- 

 tional proof that this process is still imperfectly under- 

 stood, and that much is yet wanting to complete our 

 knowledge of it. 



" Swindon, Monday evening, ( 21 st July 1788). Heat 

 of the air in the dairy-room 60° ; milk 87|° ; unco- 

 vered; came in one hour 10 minutes; whey 85° ; curd 

 of a middle quality." 



" Deyhouse, Tuesday evening. Air 63° ; milk 88° ; 

 not covered ; came in half an hour ; ' too much ren- 

 net i Avhey 86° ; the curd not tender, but far from be- 

 ing of a bad quality." 



" Westleycot, Wednesday morning. Air 60° ; milk 

 86° ; uncovered ; came in three quarters of an hour ; 

 whey 84° ; the curd of a good quality." 



" Shaw, Wednesday evening. Air 62° ; milk 87°; 

 not covered ; came in about an hour ; whey 86° (quan- 

 tity very great) ; the curd of a good quality." 



" Avon, Thursday evening. Air 60° ;. milk 88° ; 

 closely covered with a thick woollen cloth, to make the 

 top and the bottom come together ; came in about an 

 hour ; whey 87° ; the curd very good." 



" Foxham, Friday evening. Air 60° ; milk 91°; 

 covered with a thin cloth ; came in one hour ; whey 

 89° ! nevertheless, the curd delicately tender III" 



When entire-milk has been coagulated by any of the 

 above means, the coagulum afforded contains two sub- 

 stances ; one of the nature of albumen, and the other 

 of the nature of oil. The first is properly the cheese ; 

 the second, butter. But when cheese is prepared for 

 the table, the butter is not separated, because it im- 

 proves the taste of the cheese. The substances which 

 coagulate milk have all been thought to act by means 

 of the acid which they contain ; but alcohol coagulates 

 milk, and yet it contains no acid. Besides, Young, and 



more lately JParmentier and Deyeux, have shewn, that Dairy. 

 rennet retains its coagulating power, even when an ex- W "Y""""*' 

 cess of alkali is added to it. 



The vegetable acids much diluted, are observed, 

 when added to milk, to produce more curd than the Action of 

 mineral acids in the same state; and this is probably ihevege- 

 owing to the superior power which the latter have of taWe aci,1 » 

 redissolving the curd or cheese. For if one part of u P on milk ' 

 curd, newly separated, and not dried, be mixed with 

 eight parts of water slightly acidulated by a mineral 

 acid, and the mixture be boiled, the curd will be dis- 

 solved, though it would scarcely have been sensibly 

 affected by a vegetable acid thus diluted. The vege- 

 table acids, however, in their concentrated state, dis- 

 solve curd readily, and in considerable quantity; where- 

 as the mineral acids, when concentrated, have either 

 very little effect on it, as the sulphuric acid ; or decom- 

 pose it, as the nitric. By means of this last acid, a 

 quantity of nitrogen may be obtained from curd. 



The reason why neutral salts, gums, sugar, alcohol,, 

 and acids, coagulate milk, may be partly owing to the 

 superior affinity of these bodies for water ; but this 

 subject is very little understood. If milk be diluted 

 by ten times its weight of water, it cannot be coagu- 

 lated at all ; and the reason why heat alone is insuffi- 

 cient for its proper coagulation, is probably owing to 

 the great dilution of the caseous matter in the serum 

 of the milk itself. Scheele thinks the coagulation of 

 milk, as well as of the white of eggs, and of the lymph 

 or serum of the blood, is owing to the combination of 

 caloric with these substances. The alkalies, in their 

 caustic state, when aided by heat, dissolve cheese ; and 

 ammonia dissolves it more readily than potass or soda. 

 A few drops of pure ammonia added to coagulated 

 milk, quickly causes the curd to disappear. The fixed 

 alkalies, in dissolving, decompose curd; for, during the 

 solution, ammonia is disengaged ; and, if the matter 

 held in solution in the alkali be separated by an acid, 

 it is found to be no longer curd, but a black fatty sub- 

 stance like oil. 



_ Pure caseous matter is white, solid, somewhat elas- 

 tic, insoluble in cold water, but, by boiling in water,, 

 its texture is destroyed. When fresh, it is nearly in- 

 sipid, but becomes acrid on keeping. If left in a moist 

 state of the air, it very soon putrefies ; but if it has 

 been thoroughly dried, it remains a long time unchan- 

 ged. Good cheese melts at a moderate heat ; but bad 

 cheese, when heated, dries, curls, and exhibits all the 

 phenomena of burning horn. Cheese must be admit- 

 ted as a principle differing in some respects from all 

 other animal matters. It seems most analogous to al- 

 bumen, as it is soluble in a fluid resembling the serum 

 of the blood, and as it is coagulated by heat. In se- 

 veral of its other properties, it is analogous to fibrin, 

 and is probably intermediate betwixt these. It is the 

 most animalized product of the milk, and is indubita- 

 bly that which is most nutritious. When shaved thin, 

 properly treated with hot water, and mixed with quick- 

 lime, it forms a very strong and durable cement. 



If milk be much heated when it is put to coagulate, 

 and if the curd be broken, and the whey suddenly and 

 strongly pressed out, as is often the case in Scotland, 

 the cheese is worth almost nothing, but the whey is 

 excellent, and will afford much butter. But when the 

 whey is separated by a slow and gentle pressure, the 

 cheese is good, but the whey limpid and poor. Thom- 

 son's Chemistry. 



Milk having been adopted by the human race a* 



