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important that the large concerns engaged in the business employ trained men to examine the herds and ascertain that there are no diseased cows, that the stables and surroundings are in good sanitary condition, that the attendants who do the work are healthy and cleanly attired, and that the milk is properly cared for and cooled before it is delivered to the condensery.
To make doubly sure that the quality of the milk received is right, an expert, with a keen sense of taste, inspects every can of milk received, and if any unnatural flavor is detected the can of milk is rejected and returned to the producer. This extreme care is absolutely necessary, because any objectionable flavor becomes intensified and can not be eliminated during the various processes to which the milk in subjected. Milk is usually condensed in a vacuum pan, although a few concerns concentrate milk in an open pan in the following manner: The milk is run through a centrifugal separator and the cream removed. The skim milk is then pasteurized and run into rectangular vats provided with several pipes by means of which air is forced through the milk by a blower. During the process the skim milk is held at about 140° F., and the air, which is often heated by passing over steam coils, carries off the moisture in the milk, thus reducing its volume to the required consistency, usually about 4 to 1. After being thus treated it is known as concentrated skim milk. If concentrated whole milk is desired the cream which has been pasteurized is restored and emulsified in an agitator.
The equipment of a condensing plant using a vacuum pan depends upon the kind of product made, although the process used and the machinery required are similar for all condensed-milk products.
For the manufacture of "plain condensed milk" the equipment consists of a boiler, engine, scales and weigh can, receiving vats, milk heater, hot wells, vacuum pan and condenser, vacuum pump, cooling tank, and cans. If skimmed milk is condensed, a separator is necessary, as well as vats, pasteurizers, and coolers for handling the cream. In the manufacture of sugared condensed milk the same equipment is necessary as for plain condensed milk, and in addition a tank is sometimes provided for dissolving sugar before adding it to the milk in the vacuum pan. If the product is put up in cans, machines for filling and sealing cans are necessary, also for making cans when they are not purchased from outside can manufacturers.
For making evaporated milk an equipment similar to that used in the manufacture of plain condensed milk is required, except that a tubular cooler is used for cooling the product instead of the cooling tank, and machinery for filling and sealing cans is also required; also a device for sterilizing the product in the cans, and a shaker for violently shaking the filled cans after sterilization.
73029°-YBK 1912- 22
A late innovation in equipping a milk condensery is the homogenizer. Difficulty is sometimes experienced by those engaged in producing evaporated milk in preventing a separation of the solids after it has been kept for a time, the lighter solids going to the top and the heavier ones to the bottom. As homogenizing normal milk prevents (partially at least) cream from rising, it is claimed that it will have a like effect on milk to be evaporated.
The granulation of the milk sugar, which gives evaporated milk the appearance of containing some kind of an objectionable grit, is also said by some to be overcome by the use of a homogenizer. This machine, however, has not been in use sufficiently long definitely to determine its value for the purposes mentioned.
The equipment of condenseries is quite uniform, but considerable variation is noted in operating, especially in the temperatures used. It is evident that no hard and fast rules can be laid down to follow under varying conditions. The following description of the process used in making the different grades of condensed milk and the cost of equipping was contributed by a gentleman who has had extensive practical experience in its manufacture and in manufacturing and installing such machinery, and probably is as nearly correct as can be obtained:
"Plain condensed milk" is made from whole milk, from part whole and part skimmed milk, and from skimmed milk. To get the desired density it is necessary to condense the whole milk 3 to 1 and the skimmed milk about 4 to 1. The milk to be condensed is put into hot wells and heated with steam to a temperature of 150° to 156°. It is then drawn into the vacuum pan and condensed, if whole milk, to 10° Baumé, and if skimmed milk to 14° Baumé. As soon as the desired density is reached the milk is then superheated by blowing steam into the milk in the vacuum pan until the milk becomes thick. The temperatures used in this process vary from 175° to 200°.
As soon as the milk is sufficiently thick the steam is shut off and water is run into the condenser to secure the proper consistency. The vacuum pump is then started slowly, and the vacuum drawn up to about 26 inches. The vacuum is then released, and the milk is drawn into 10-gallon cans and placed in the cooling tank and cooled to 36° or 38° F. by first cooling as cold as possible with water and then shutting off the flow of water to the cooling tank and turning the brine or ammonia through the coils in the side of the cooling tank.
Sugared milk to be put up in cans is made from whole milk and is condensed 4 to 1 and 1 pound of sugar added to each 3 quarts of milk condensed. The milk is heated in the hot wells as hot as possible by steam blown into the milk through a heater head. It is then drawn into the vacuum pan and condensed. There are different methods used in adding the sugar to the milk. Some manufacturers have a separate tank, where the sugar is dissolved either in hot milk or hot distilled water, and the sirup so made drawn into the vacuum pan gradually with the fresh milk; others draw nearly all the milk into the vacuum pan and dissolve the sugar in the hot wells in the milk left there for that purpose. It is then drawn into the vacuum pan after the milk is condensed. Sugared condensed milk to be sold in bulk is made from part or all skimmed milk in the same way as the canned goods, except that 1 pound of sugar is added for each 4 quarts of skimmed milk to be condensed. This class of goods
is used by bakers and confectioners, and is made with any desired per cent of butter fat from whole milk to full skimmed milk.
As soon as it
Evaporated milk is made from whole milk and is heated in the hot wells the same as for sugared condensed milk. This milk is condensed in the vacuum pan until it has the required percentage of solids and butter fat desired by the manufacturer. After the milk is condensed it is run over a pipe cooler and cooled to about 60° and is then put into small cans and sealed. is sealed it is put into the sterilizer and heated to about 240°. sterilizer the milk is kept in motion, so that the contents of the heated through evenly. The time required depends upon the size of the cans and the condition of the milk and varies from 18 to 45 minutes. As soon as the milk is sterilized it is immediately cooled in the sterilizer, and when cold it is removed from the sterilizer and shaken in a shaker until it is smooth.
cans will be
A small condensed-milk plant for making plain and bulk-sugared condensed milk with a capacity to condense 10,000 pounds of milk a day can be built complete for about $7,500; a 20,000-pound capacity plant will cost about $13,000, and a 40,000-pound capacity plant will cost about $20,000. The above estimate is based upon complete equipment and plain but substantial building.
The cost of the plant to make canned goods depends largely on how completely it is equipped and whether the cans are manufactured in the plant or purchased from some can-manufacturing company. The cost of canned-goods plants ranges from $20,000 to $200,000, depending on the size and style of the equipment and building. It is not practical to make canned goods where the milk supply is less than 15,000 pounds per day.
DEVELOPMENT OF THE DESICCATED-MILK INDUSTRY.
Practical processes of converting cows' milk into dry milk powder are of comparatively recent discovery. According to the best authority, descriptions of such processes were first published in 1901, although it is claimed that skim-milk powder had been successfully made prior to that time.
A consular report from Sweden dated November 20, 1901, refers to a process reported to the Academy of Agriculture held in Stockholm, Sweden, that month, and the New York Produce Review and American Creamery, dated January 1, 1902, refers to a similar process used in America and claims its discovery prior to the Swedish process. Since that time the processes have been considerably improved and several different systems have been evolved. Several factories have also been established, both in this country and in Europe, for the manufacture of this product on a commercial scale.
The market at the present time is mainly with bakers and confectioners, but when the nutritious properties and keeping qualities of dry milk are better known it may become a household article of
SCOPE OF THE INDUSTRY.
In May, 1911, there were 10 factories engaged in desiccating milk in the United States, located in five States, namely, Vermont, New Jersey, New York, Michigan, and California. The amount of milk powder produced in the calendar year 1910 by the various plants in the country was approximately 8,500,000 pounds. The capacity of the plants then in operation was 891,000 pounds of liquid milk per day of 10 hours, or 325,215,000 pounds per year. Assuming the yield of dry milk to be at the rate of 9 pounds to 100 pounds liquid milk, the yearly capacity of dry milk for the plants then in operation was 29,269,350 pounds.
The machinery for drying milk is specially constructed for the purpose under various patents, and is, therefore, expensive. Factories are often equipped with apparatus made by mechanics in the vicinity of the plant, although there are manufacturers who make such machinery on order. The various systems are generally protected by patents, and already more than 60 patents have been issued covering devices for making this product.
Drying milk from which the fat has been removed seems to be a success. It converts a wholesome and nutritious article of food into a condensed form, convenient to handle and transport, and ready at all times and under any circumstances for immediate use whenever and wherever wanted. Milk is changed by the drying process from a quickly perishable, bulky, and inconvenient substance to transport into a product requiring comparatively little space, and its keeping qualities are practically unlimited.
Probably over 90 per cent of the milk powder produced at the present time is made of skim milk. From 100 pounds of whole milk of average quality 3.5 pounds of butter fat and 9 pounds of dry skim milk can be secured. Dry skim milk powder has the appearance of ordinary flour made from grain. It absorbs moisture readily, which must be avoided by using containers that are as nearly as possible air tight and moisture proof and by storing in cool, dry places. This grade of dry milk possesses in a condensed form all the valuable properties of fresh sweet skim milk. It can be used in the dry form by bakers and confectioners, or, if desired, it can be converted back to its original liquid state by adding the amount of water that has been extracted from it. In drying whole milk more difficulties are encountered. The keeping qualities of dry whole milk
are not equal to those of skim milk. The fatty part has a tendency to become rancid, and, where rancidity does not develop, when some months old it loses its freshness and lacks the fine flavor of fresh milk; at least such has been the case with samples tested under the writer's observation. Its keeping qualities are superior to those of liquid milk, however, and it is a very desirable substitute when fresh milk can not be obtained.
Besides milk powder from whole milk and from skim milk, there are upon the markets intermediate grades, frequently sold under coined names. It may be well to state that dry whole milk of average quality contains about 27 per cent fat, varying somewhat according to the richness of the milk. In some instances whole milk reinforced with cream has been dried which contains from 30 to 40 per cent butter fat.
Two distinct methods of drying milk are in use, from which several systems have been evolved. In one method the milk, in the form of a spray, is forced into a chamber of hot air, with an air current driving the dry particles against a screen, which arrests the solid portions and allows the air to pass on. A more general device is the heated cylinder, to which milk is caused to adhere in a film, quickly drying, and, as the cylinders revolve, the dried matter is scraped off in sheets or ribbons. These are collected and, if necessary, further dried and then reduced to a fine powder. In most instances the milk is partially condensed in a vacuum pan before entering the drying machine.
The following extracts from authorized descriptions of some of the various systems in use will give a general idea of the modification of the two methods above described:
As the milk is received at the factory it is filtered through cotton as it passes to the receiving vat. From this vat the milk passes directly through a heater, where the temperature is raised to 90° F., and without stopping in its flow it passes to a battery of separators, which remove the butter fat and at the same time further clarify the milk. The cream from the separators passes to a pasteurizer, which not only heats but promptly cools again. The cream is at once run into cans and placed in cork-insulated pools, which are cooled to a low temperature by brine coils supplied by an artificial ice plant. The cream is later taken from the pools and reunited with the separated milk for the higher grades of powdered milk. The separator milk flows directly to a pasteurizer and, after being reduced to a low temperature, flows at once to an insulated tank, from which it is drawn directly to the exsiccators. The exsiccator