REFRIGERATING CAVES AND CELLARS.

Lyttelton Times, Volume LI, Issue 5590, 24 January 1879, Page 7

REFRIGERATING CAVES AND CELLARS.

(From (ho Colonies and India, Oct 12). In the south of France—at Roquefort, in the Ayeyron—are certain natural caves which exhibit a peculiar and long unexplained phenomenon. The temperature in them is always considerably below the mean annual temperature of the locality. That the coldness is caused by draughts of air which traverse the oaves has long been known, but the cause of the draughts themselves has been the subject of the wildest and most erroneous conjectures. Some hare asserted that the outer air is drawn down into the caves; althoMgh why this should be or how it should account for the temperature in the caves being near freezingpoint, when that of the outer air is* at 86deg. Fahr., is not stated. Others have alleged the existence of beds of perpetual ice buried in the earth, the surfaces of which they suppose to be traversed by the outer air in its passage to the caves. This explanation has failed to satisfy the geologists, who know very well that no such deposits of ice exist. Olivier de Serres appears to have had this idea in his mind when he wrote—“ Glaciers have become buried by the fall of boulders and detritus, and, being protected from the air, remain in a frozen state. The slow melting of these glaciers gives rise to a spring, which is found below the town, and the water of which is always ice-cold.” But while science was puzzling herself to discover the causes of the phenomenon, a local branch of industry managed to turn it to practical account, it having been discovered that cheeses kept in these caves were much superior in quality to others which had not been so treated.

In a charter of the year 1070 we find that one Flottard de Cornus undertook to supply the monastery of tho town of Conque yearly with two cheeses from the Roquefort caves. From this time the Roquefort cheese has been gaining in repute. In 1790 the annual production was 5000 cwt. Now it amounts to between 3,000,000 and 4,000,000 kjlogs. (3000 to 4000 tons), which commands an assured sale. This steady increase in the demand for the article has, of course, contributed to the prosperity of the district, which has become wholly changed in its circumstances thereby. Formerly there were but a few small farms on the exposed plain of Larzao, where a scanty herbage afforded feed for a few sheep, the number of which was restricted by the scarcity of food. Now there are artificial meadows and thriving flocks, whose numbers expand as the prosperity of the population goes on increasing. The radius of production has also increased, and now extends several miles around the locality where the far-famed cheese was originally manufactured. In view of these advantages a question has naturally suggested itself as to the possibility of imitating the process in localities where large numbers of sheep are kept, of whose milk no use is at present made, although it might be turned to account in the manufacture of an article for which there appears to be an increasing demand in the world. To discover the secret of the temperature in these oaves, so as to enable tho process to be imitated as perfectly as possible in natural or artificial caves elsewhere, M. Charles Blondeau recently undertook a personal examination of them. He found that the draughts were produced by air-ourronts entering through long natural passages, traversing the side of tlie mountain in which the oaves are situate and communicating with the outer air. The cause of the refrigeration of the air in its passage was the next question. The nature of the soil afforded the necessary explanation. There is a constant drip of water in the air passages. This gives rise to incessant evaporation and an attendant reduction of temperature, the reduction of temperature so produced being communicated to tho adjacent air. The specific gravity of tho air is thus increased, causing a downward current into the oave. The reduction in temperature is further increased by the contraction of the air-passages at their inner extremities, producing a considerable compression of the descending air, which expands again after entering the cave. Experiment has shown that air saturated with watery vapour and injected through a narrow orifice becomes chilled almost to the point of congelation, when it expands again. Hera, then, is a full solution of the mystery. Once clearly understood, nothing con bo easier to reproduce than the phenomenon. It will suffice to find or dig a oave at the foot of a hill or at a sufficient depth from the surface, and to plaoe it in communication with the external air by means of a conduit formed in the side of the hill, with water trickling over its interior surface. If depth of soil sufficient to give the conduit a suitable length cannot bo found, an artificial chimney must be built, lined with slag bricks, coke, or rough stones, over which water must be allowed to trickle, the evaporation of which will produce the requisite reduction of temperature and cause the air to precipitate itself into the cave in a chilled current.

It may be asked bow it happens that a temperature as low as that of the Roquefort oaves, which appears to arrest all kinds of fermentative action, can improve the quality of the cheese. Tho answer ie, that certain ferments require a low temperature to develop with rapidity. The first transformation of the casein is duo to Penioillium glaucum, whioh at high temperatures scarcely develops at all. At the temperature of the refrigerating oave, on tho contrary, it develops fast, transforming tho casein, whioh is dry and tasteless, into a fatty substance of a peculiar and agreeable flavour. At Roquefort the coldest oaves have tho best repute, and are those in whioh the “ ripening ” or transformation of tho casein is most complete. Besides the refrigerating caves, the temperature of whioh is always about 40deg Fahr., or under, there are other oaves at

Roquefort which are hot traversed by draughts of air, and wherein the temperature is usually about SOdog Fahr. These are called “ bastard-cares,” and the cheese placed therein never acquires the same quality as that in the colder caves. The deficiency could no doubt be supplied artificially, as above suggested. There are other industriol uses to which such oaves could bo put, as, for example, brewing, particularly browing on the Bavarian system, in which the quality of the beer depends on the. maintenance of a-low temperature in the fermenting wort. In Bavaria and more northerly countries, these low temperatures are maintained by the liberal use of ice in large quantities, so that the temperature of the wort never exceeds 42tleg. to 46deg. Pahr. But in warmer climates ice could not generally be used in sufficient quantity without great expense. Here, then, is an opportunity for the refrigerating care, which would allow of the maintenance of a uniform temperature low enough to prevent the occurrence of lactic fermentation, which takes place between the temperatures of 68deg. to 77deg. Fahr.: or of acetic fer mentation, which commences at temperatures of 86deg. Fahr. and upwards. Caves of this description, or cellars constructed on the same principle, would prove verv serviceable for keeping provisions, wines, beer, &c, in hot weather, and for various purposes in manufacturing art where low temperatures are desirable or indispensable.”