REFRIGERATION AND CHEDDAR CHEESE.

New Zealand Journal of Agriculture, Volume XXIX, Issue 6, 20 December 1924, Page 394

REFRIGERATION AND CHEDDAR CHEESE.

CURING, STORAGE, AND TRANSPORT

Paper read by WALTER WRIGHT, Inspector of New Zealand Dairy Products, London, at the International Congress of Refrigeration, London, 1924. I desire it to' be understood that the matter contained in this paper deals only with cheese , of the Cheddar variety, and has been based upon methods adopted in the export trade of cheese from New Zealand. It will be readily understood that owing to the geographical position of New Zealand such development of trade could not. have been made • possible without the aid of mechanical refrigeration.. One of the most important factors, in the production . of Cheddar cheese of a good sound commercial quality is that of adequate control of temperature, not only as applied to the manufacturing and storage branch of the business, but also in the . care of the raw material which the cheesemaker has to handle in the production of such cheese. Probably one of the weakest points in the cheesemaking industry to-day is the lack of this most essential feature in the handling of milk at the source of production— is, the dairy farm. To enable farmers to deliver their milk to the cheesefactory in the best possible condition they must have at their command some effective system of cooling the milk, at all times having in view the desirability of reducing temperatures from blood-heat in the shortest possible time after the milk is drawn from the cow. With regard to this phase of the industry I feel that there is the need of some small but efficient type of refrigerating-machine, obtainable at a reasonably low cost to farmers, that could be run in conjunction with a direct-expansion cooler for the purpose of cooling the milk immediately it is drawn from the cow. I suggest that this is a matter worthy of the consideration of not only dairy-farmers but also of manufacturing engineers. Undoubtedly in some countries, where large quantities of milk are handled by individual farmers, there should be a . market available for small machines of this type. COLD CURING. Although it is some twenty years since experiments were carried out at the Wisconsin Experimental Station by Babcock, Russell, Vivian, Barr, and others, the full application of the principles of cold curing of cheese is far from being a general dairy practice so far as Cheddar-cheese production to-day is concerned. This is somewhat surprising, because the initial cost of .installation of mechanical refrigeration is not great, and such costs are rapidly obliterated by the saving in the loss of weight and the improved quality of the cheese so treated during the process of curing. As is well known, cheese loses considerable weight after being manufactured, but such loss is governed in extent largely by the temperature of the atmosphere to which the cheese has been submitted. It therefore follows that the lower the temperature consistent with safety and a normal ripening of cheese, the lower will be the loss caused through the evaporation of moisture.

Probably the most important feature in cold curing of cheese — between 45 0 and 50° F—is the improvement in the flavour : when compared with cheese that has been cured in curing-rooms where no satisfactory arrangements have been made for the control of summer temperatures. Experience has taught us that the cheese can be taken from the press. and placed on the shelves in the curing-room, where temperatures are held between 45 0 and 50° F., with perfect safety so far as the ultimate condition of the cheese is concerned. Cheese cured or ripened in such temperatures have, almost without exception, been found to develop a mild clean flavour, and with increase of age is found to retain those characteristics. This indicates that at the lower range of temperature the desirable colonies of bacteria or enzymes continue their work normally, while those of the undesirable type suffer a severe, check on account of the temperatures being unsuitable for the development of the undesirable flavours that develop so exceedingly when cheese is ripened at high temperatures such as those of midsummer. Like many other old-fashioned theories in the world of cheesemaking, the theory that comparatively- high temperatures are necessary for the normal ripening of cheese has been entirely upset, as is illustrated by the practical results obtained by the cold curing of cheese to-day. Respecting abnormal fermentations, cheese is so admirably adapted as food material for the development of bacteria, many kinds of which are able to produce deleterious changes in it, that the influence of temperature on the rate of such bacterial activity, is a matter of. considerable moment. Gassy cheese is particularly associated with high-temperature curing. Regarding body and colour, it has also been found that cheese cured at 33 0 to 40° F. when cut presented a perfectly solid even appearance and remained so as the curing progressed, while when cured at 6o° F. the cheese were more or less open and frequently bleached, presenting a mottled appearance, which increased as time went on. Further, the experiments conducted show that through the slower ripening the cold-cured cheese keeps in good condition much longer than that where rapid ripening takes place under higher temperatures — a fact of considerable importance to the cheese-dealer who may have to carry the cheese for some time. A bacteriological examination of cheese held in cold store fourteen and seventeen months showed, when the cheese was removed from cold storage, that lactic-acid-producing forms and inert species were most abundant ; very few liquefying and no gas-producing organisms were found. (Bulletin 94, Agricultural' Experiment Station, Wisconsin.)The benefits of the application of cold curing of cheese can be summed up as follows : (1.) It delays the curing not more than a week or ten days. (2.) It effects a direct gain by saving from 1 cent, to 11 per cent, in the shrinkage of cheeses that have not been paraffined during the period of curing. (3.) It eliminates the heated flavour and mealy texture that are characteristic of all ordinary cured cheese in hot weather. (4.) It tends to prevent the development of undesirable flavours in many cheeses which would otherwise be very inferior on that account. (5.) It protects the cheesemaker in some measure from merchants' claims arising from causes over which he has no control. (6.) Cheese which has been properly cold-cured does

not require subsequent storage at extremely low temperatures to check the injurious processes which are set up by high temperatures, but may be kept in good condition with that nutty flavour essential to Cheddar cheese. (7.) The general improvement in the quality increases the consumption of cheese enormously, and, by thus increasing the demand, ensures a better average price. (Report of the Dairy Commissioner, Canada, 1906.)

It will be noted that both the authorities quoted appear to be entirely in accord as regards the benefits to be derived from the policy of cold curing. In New Zealand to-day the tendency is to take an intermediate course by adopting a temperature of from 45 0 to 50° F. for the curing-rooma practice that is giving good results, and, so far as my investigations have gone, this system is working quite, satisfactorily and beneficially. It has to be realized that when cheese . has been' submitted to the ill effects of high temperature its quality suffers irreparable injury, which can only result in disappointment to the maker, financial loss to the owner, and dissatisfaction on the part of the buyer. Where such damage has taken place I know of no practicable steps that could be taken to eliminate the injury that the quality of the cheese has sustained. It is most important that all vehicles for the conveyance of cheese from, curing-room to cold store should be in such a condition as to prevent any damage to the condition or quality of the cheese during transit. Not infrequently this is a stage in the handling of cheese where it sustains damage owing to the lack of proper control of high temperatures. COLD STORAGE. In regard to the cold storage of cheese it has been found that the wet-battery system gives the best results, with air-temperatures in the chambers held at between 40° and 50° F. for short storage. For long storage, however, temperatures can be reduced with safety to 36°. and give satisfactory results. Holding cheese at about this temperature has proved to be beneficial in that it retards the development of mites and moulds very materially. To ensure the safe and satisfactory cold storage of cheese packed in cases it might be well to mention here a few of the essential points that must be observed if results are to be satisfactory. (1.) It is most important that the cheese should be in a fit condition for packing. The cheese should be at least fourteen days on the shelves of the curing-room, or longer if necessary, so that the rinds and tops and bottoms of the cheese may become dry and firm. To enable this to be done it is necessary that the cheese should be turned once every day during this period. If the cheese is packed before that time there is the danger that it will not stand any length of cold storage satisfactorily. There is a probability of the cheese turning out in bad condition, particularly on the tops and bottoms, . because, if the rinds of the cheese are moist and soft at the time of packing, and it is placed in cold storage in that condition, putrefaction will eventually develop at the points of contact between the cheese and timber. The result is that if held for any lengthy period without attention such portions of the cheese will eventually become unfit for human consumption.'

(2.) It is imperative that no cheese should be stored away in any but. dry and thoroughly seasoned packages, and scale-boards should always be used. If this safeguard is neglected and the cheese is packed in green and wet timber the condition of the cheese will be found on being withdrawn from storage to be unsatisfactory, owing to the crowns having become soft and pappy and in a more or less state of decomposition, according to the time the cheese has been held in cold storage and the degree of moisture to which it has been subjected. (3.) The question of' an efficient air-circulation in the chambers has to be considered. To obtain satisfactory results all chambers require to be fitted with trunks to take the air as drawn from the battery by the fan to the several points. - A system that provides trunking, with delivery-ports on one side and outlet on the other or return side of the chamber, has been found to give good results. From experiments and experience it has been found that it is better to have a large circulating-fan, thus moving the air at a comparatively slow velocity, but at the same time sufficient to keep the air moving, than it is to use a small fan driven at increased speed moving the air at a high velocity. The latter method has a tendency to crack the rinds and dry out the cheese, as it practically subjects it to what might be termed a “ forced draught ” treatment. . (4.) A proper adjustment of the air-delivery ports is most important, and requires frequent attention so as to provide an equable discharge of air-currents. Whatever the speed of air delivered from the various ports may be, it is advisable to use baffle-boards when the cheese is stacked close to .and in direct line with the air-delivery, so as to prevent the drying-out of the cheese on which -the direct air-current would otherwise impinge. Where large quantities of cheese are stored the use of large canvas screens is beneficial in the gangways between the stacks for deflecting the air-circulation through the stacks of cheese. This assists in keeping temperatures more uniform in large chambers that are filled with cheese. Temperatures are found to be irregular when there is no adequate air-circulation.. Air-circulation also carries off any excess moisture there might be in the chamber. (5.) The humidity of air can be governed, within certain limits, by the density of calcium-chloride brine that is running over the directexpansion coils of the battery. If the air is allowed to become too dry considerable loss in weight will take place, and cracked rinds will also be the result. On the other hand, too heavy moisture will cause heavy condensation to settle upon the cheese, which, if allowed to continue for any length of time, will cause decomposition, commencing on the outside of the cheese and working inwards. Cheese submitted to such conditions will, in the space of a few weeks, begin to show decomposition, particularly on the crowns or tops and bottoms of the individual cheeses. ■ ‘ (6.) With reference to adequate cooling-power in the matter of cheese storage, herewith is presented a plan of the first, second, and third floors of the cheese-store of the Auckland Farmers' Freezing Company. These rooms form part, of and are attached to a large block of buildings owned by the same company, and used for the storage of butter, cheese, fruit, &c., and for the manufacture of clear can ice. Each of the three stories forms one large self-contained storeroom

containing 66,000 cubic feet of space, each room being provided with an independent battery for cooling and purifying the air, together with the necessary air-trunks. The building is of brick, plastered on the outside, four stories high, and roofed with asbestos tiles. The insulation of the walls is 12 in. of calcined pumice contained between the brickwork and a 6 in. by 1 in. tongued and grooved lining nailed to 6 in. by 2 in. studs, the face of the studs being 12 in. from the brick wall. Between the brickwork and pumice and between the lining and the pumice is a layer of hard felt, in. thick, saturated with bitumen. This serves a double purpose prevent moisture getting into the pumice,. and to retard air-filtration, which also carries moisture into the insulation. The floors and ceiling are all insulated with 12 in. of pumice filled in between the joists. Bituminous felt is stretched on the under-side of the joists. before the 6 in. by 1 in. tongued and grooved ceiling-boards are nailed up, and the pumice is then filled into the space between the joists and flush with the top ; another layer of felt is put over this before the flooring-boards are nailed down. All crates and cases are taken up or brought down by swinging-tray elevators capable of handling thirty crates per minute. These are fitted with loading and discharging grids on each floor, so that the cheese can be transferred from any floor to any other at this rate. Roller chutes are also used to a considerable extent. The refrigerating plant for each room consists of 2,400 ft. of in. ammonia piping in two coils. These coils stand in a steel tank 12 in. deep. Beyond the coils in the direction in which the air flows is a “ stack ” of battens on edge, or corrugated galvanized iron on end. Chloride-of-calcium brine is drawn from the tank by a centrifugal pump, and discharged in a shower by suitable sprinklers over the expansioncoils and stack. Ammonia is expanding in the coils and cooling the brine as it runs over the coils ; this cold brine on being showered over the stack further reduces the temperature of the air which comes in contact with it. At the inlet end of the battery is a propeller fan having a theoretical capacity of 30,000 cubic feet of free air per minute, but in actual practice the amount is very much less than this. It is estimated that the air in the chambers is circulated about fifteen to twenty times per hour. (In more recent practice the fan is placed at the outlet end of the battery and the air drawn through the coils and stack.) The fan and pump are driven by a suitable electric motor. In connection with this system it is necessary to provide some means of concentrating .the brine, as any moisture evaporating from the cheese is condensed in the battery and increases the volume of the brine, and, of course, weakens it. In concentrating the liquid by boiling, the characteristic flavours of cheese are driven off and the brine purified, but there is a limit to the extent to which this can be carried out, as in time the brine becomes “sick” and. must be renewed. By increasing or decreasing .the density of the brine the humidity of the air in the chamber can be controlled within certain limits. The density of the brine should be maintained at a point at which it will not freeze on the coils, and which will maintain a percentage of humidity suitable for the cheese during storage. This

method of cooling and washing the air at the same time keeps the air in the chambers in a clean, sweet, and dry condition. The reason for circulating such a large volume of air per minute is . that it eliminates great-differences in temperature. In this plant the greatest difference of temperature in the battery and storeroom does not exceed two degrees Fahrenheit. The Auckland Farmers' Company has freezing and chilling rooms with a total capacity of nearly two million cubic feet, operated with air-circulation and wet battery. In one case the battery contains 52,000 ft. of i|in. piping. For these details I am indebted to Mr. T. Simpson, managing director of the company. (7.) My experience has been that the amount of gas thrown off by the cheese during the early stages of cold storage is governed very largely by the temperature of the cheese when it is first placed in cold store. The higher the temperature of the cheese at that time the greater will be the exudation of carbon dioxide. Mr. F. W. Grainger, then manager, West Coast Refrigerating Company, Patea, New Zealand, supplies the following notes regarding the storage of cheese at his company’s works : — “ Cheese in cold storage gives off a considerable amount of - gas, which in time makes the chambers very foul. This must be got rid of by blowing out the chambers through special -ports, and taking in fresh air at the inlet end of the cooler. But we find by boiling our brine, taking a portion from each of the - coolers every day for concentrating,, thus getting rid of moisture taken up by the calcium chloride, and keeping the brine - density constant and adding the fresh concentrated brine, that we eliminate the gases as they are taken up in the calcium chloride and got rid of by boiling. This, in my opinion, is better than adding humid air from the' atmosphere, as the latter tends to assist mould-growth on the cheese. The brinecirculating pump is fitted with a suitable bypass connection for taking out weak brine and delivering it to the concentrator, and for returning concentrated brine to replace the quantity taken out. It is an important point to make sure that brine is the right density, and to ensure an even flow over the coils so that they do not freeze over with a coating of ice, in which case the efficiency of the cooler will be lost.”, OCEAN TRANSPORT. . Shipping companies in the New Zealand trade have not yet adopted a uniform system of refrigeration on board the various vessels as far as the carrying of cheese cargoes is concerned. The systems in use might be briefly described as follows : (1) Brine-circulation ; (2) aircirculation from expansion batteries; (3) air-circulation ' from side grids. The following examples afford a brief description of the arrangement of the pipes and the fitting up of the various chambers : — Brine-circulation : Capacity , of chamber, 37,100 cubic feet pipe measurement used, approximately 3,700 ft. run over piping 2 in. O.D. ; insulation used, silicate cotton. The method of brine refrigeration is that cold brine of a suitable temperature' for maintaining the required temperatures in the cheese-chambers is pumped continuously through brine-piping, being arranged in the form of grids and secured to the sides, bulkheads, and roof of the chamber. The feet-run and

disposition of the piping used is adjusted by the engineer, who can control the circulation from the refrigerating-machinery room to suit the conditions in the cheese-chambers. In this style of chamber no arrangements are made for air-circulation. The insulation used varies in different vessels, and charcoal, silicate cotton, and granulated cork are all good insulating-materials, the latter, however, having been used in all the later vessels. . > • Air-circulation from expansion batteries: Capacity of chamber, 27,800 cubic feet ; insulation' used, charcoal ; air-circulation per hour, 3,000,000 cubic feet for. two fans size of fan (2 off), 5 ft. ; fanrevolutions, 300. The cheese-chamber referred to under ' this heading is one of six cargo-spaces, having a total cubic capacity of about 285,000 ft., . and the vessel is fitted with two ammonia expansion batteries and two fans, one for each battery. The practice is with a full cargo of frozen meat and dairy-produce to work both fans and batteries, although one installation—that is, one fan and one battery —is sufficient to' maintain , required temperatures in all insulated chambers. . ’ . . Air-circulation from side grids : Capacity of chamber, 34,312 cubic feet; insulation used, granulated cork; . air-circulation per hour, 300,000 cubic feet; size of fan, 20 in. sirocco. The arrangement of this system of refrigeration consists of converting the brine-grids on the sides and bulkheads of the chamber into an air battery by fitting planed boards in portable sections in front of the grids, forming a i2-in.-wide air-duct ah round the sides and ends of the cheese-space. A series of air-holes are cut in the wooden shutters, and the sirocco fan circulates the air across the chamber, the suction being ' at' one side and the delivery at the opposite side; the 20 in. fan is used exclusively for the chamber referred to. . Details of these systems are from Messrs. .William Replen, Son, and Swinston, refrigerating engineers, London. / The successful carriage of cheese in ocean steamers is governed very largely by the condition and temperature of the cheese when being shipped, and, from personal observations, I am of the opinion that the temperature of cheese intended for long-distance transport should .be reduced to approximately carrying temperatures before being placed on board ship. If it were possible to carry out the same methods of observation and control on board ship as are adopted in cold store on land, precooling would not be so important ; but as such is not possible it is essential that cheese-temperatures be comparatively low in the first instance if the best possible results are to be obtained. Before passing on I would like to record my opinion that at no period during the life of cheese, from the time of manufacture until it reaches the retailer’s shop, should there be any need for precooling, because at every stage of its life the temperature should be controlled right along the line. It should be remembered that in the transport of cheese it is not possible to use a treatment similar to that adopted with frozen produce. Frozen produce is delivered on board ship in a frozen condition, and all that the steamship people are required to do is to hold the produce at the requisite temperature.

Experience has taught us that the higher the temperature of the cheese when taken on board the greater are the difficulties that

engineers have to contend with, and the most careful and watchful manipulation of the cooling system becomes necessary. The higher the temperature of the cheese the longer will be the time before the air of the hold can be reduced to the required temperature, say, 40 ° to 45 0 F., or the figure that may be stipulated by shippers, owing to .the danger of creating undue condensation, which, settling on the cheese, brings about rapid deterioration in the condition of'the cargo. Taking, for instance, a shipment of cheese at an average temperature of, say, 60 0 to 65° F., it will be some nineteen to twenty-one days before the air in the hold can be reduced with safety to the temperature required. ■ ■ ■ Under such conditions it will be easily ' understood that in addition to the deterioration in condition of the cheese the quality is likewise. seriously affected, owing to the rapid ripening process and the undesirable development of ill flavours common to high temperatures. At the same time such conditions favour the growth of gasforming bacteria, which adversely affect the texture of the cheese by causing the formation of gas and other holes or openings of various types, and' at the same time bring about a looseness of texture, all of which are most undesirable in cheese of the Cheddar type. In the stowing of cheese in the holds it is important that there should be no dripping of moisture from the brine-pipes or trays overhead. Personally, I do not recommend the use of overhead grids in the transport of cheese, owing to the danger there is of damaging the cheese that may be carried underneath; It is also important that there should be a clear space of, say, 12 in. between the side grids and timbers, and false bulkheads should be carried from the ceiling to. the deck of the hold so that no cheese can be stowed underneath the grids or scuppers, the latter being erected to carry off the moisture from the brine-pipes. In cases where these precautions have not been taken certain quantities are not infrequently landed in a more or less damaged condition. Until quite recently the common practice has been to carry cheese in the 'tween-decks of the vessels, but owing to the great increase in the quantity it has also become necessary to carry it in the lower holds, and results have been, on the whole, fairly satisfactory. .With regard to the temperature in. the cheese-holds, I have found by experience that temperatures in different parts of the hold are variable. For instance, taking a cheese-chamber in which the depth of the hold will allow the cheese to be stacked-, say, from eight to ten tiers high, I have repeatedly found that the temperatures rise approximately one degree for each tier in the elevation. This I believe to be caused through the lack of efficient power for the complete circulation of air in the holds. In conclusion, I desire to emphasize that it is just as important to have efficient air-circulation in the cheese-holds on board ship as it is in the cold stores, because efficient air-circulation means uniform temperatures, and also, what is probably as equally important on board ship, the drawing-off of carbon-dioxide gas when heated cargoes have been taken on board. •