Journal of the Society of Dairy Technology, Vol. 16, No. 2, 1963 101

R E C E N T D E V E L O P M E N T S I N H A N D L I N G F L U I D M I L K

B Y J A C K M A T T H E W S

The A.P.V. Co. Ltd. Paper given to the Northern Ireland Section on December 12th, 1962

I think it is a good thing to pause now and again to review recent developments, progress and change, as this gives us a basis on which to try and peep into the future and shape our course accordingly, instead of finding ourselves overtaken by events, usually with surprise, and quite often with regret.

I shall confine my remarks entirely to the liquid milk industry, as to deal with manufactured milk products would be much too wide a field for this address, and I intend to he quite provocative.

Developments on the farm 1 think we can record as rapid and as basic changes on the farm as anywhere in the line between the cow and the consumer. In recent years many changes have been made in the milking machine, both in its efficiency, reliability, effect on the animal and general hygienic construction and ease of cleaning. A few years ago an immersion cleaning technique was introduced which is not only extreme- ly efficient, successful and reliable, but cuts down the drudgery of cleaning to literally a few minutes each day.

Direct-to-can machine milking is now quite com- mon, and entirely eliminates the possibility of con- tamination between the cow and the actual milk churn. For bigger installations pipeline milking is becoming common andcan be linked withcirculation cleaning.

Several attempts have recently been made to design individual measuring equipment for record- ing the yield of each cow instead of weighing, and undoubtedly one or other of these devices will be perfected in the very near future. Storage of milk in a bulk tank on the farm for subsequent collection by tanker is now known to be a thoroughly economic proposition and is extending in several countries of the world.

This leads me to comment that the transport of goods in industry has been undergoing quite a revolution during the past few years, and milk is no exception. lnstead of packing and unpacking and handling in crates, boxes, cms. or tins, there is a wide tendency to employ bulk trrwport methods direct from the point of productioiiinr at least a central store to the point of consumption. We see this happening with sugar, oil, cement, beer, ferti- lizer, flour and animal feeding stuffs.

There is undoubtedly considerable saving in cost, and as far as milk is concerned, there is much less risk of contamination, it is easier to gauge the

contents, and insulation against warm weather is a comparatively simple proposition. The most recent development is the experimental use of a bulk collection tanker in which the contents are drawn into the tanker by vacuum instead of having to be pumped.

Increased capacity of dairy plant My next major point is to note the general increase in unit capacity in milk handling equipment. I mean the actual throughput in gallons per hour of pasteurizing plants, bottle fillers, homogenizers, evaporators and so on. Not very long ago the general run on milk pasteurizing plants was about 200 or 400 gal/h, whereas today the minimum is usually about 1,000 and we are tending frequently to get up to 2,000 and even 3,000 gal/h in one unit. My company is quite well placed to trace this development as we have recorded the average number of heat-exchanger plates which we fit to each frame, and this has about doubled in the last ten years. At the 1962 Dairy lndustries Exposition in Atlantic City very large capacity equipment was shown. One plate machine, for example, was demonstrated which can handle between 6,000 and 8,000 gal/h. A homogenizer was shown rated at 6,000 gal/h driven by a 300 hp motor, and several separators and clarifiers were rated at 4,000-6,OOO gal/h.

These bigger operating units involve increasing problems in storage, and one very interesting development in America is the concept of the silo storage tank which is being constructed in sizes of up to 40,000 gal in a vertical form and ms?y be as much as 30 ft high. These tanks are usually erected outside the main building so as not to occupy valuable floor space, but the manway and vent and other operating points are usually constructed so that access is obtained from the inside of the dairy itself. They are not, as yet, in general use, and the initial ones have disclosed quite difficult problems which are not yet entirely solved. First of all they must be filled from the bottom; secondly, it is important to provide adequate venting to prevent collapse of the tank during emptying and while these tanks certainly cannot be cleaned by hand, pressure spray cleaning is by no means easy to install.

Let us consider the reasons for this development. 1 think in the first place we are witnessing consider- ably more intensive production on the farm itself. In the old days it was considered a good day's work

102 Journal of the Society of Dairy Technology, Vol. 16, No. 2, I963

if a man could milk 10 cows twice a day, whereas today one man handling 60 cows in a modern parlour is quite commonplace. Then 1 think in farming generally, and particularly dairy farming, there is a tendency to specialize so that all thought and effort go into the production of milk and less are diverted to other branches of husbandry. Rationalization of milk processing units offers much more efficient utilization of manpower, as one man can as effectively control a 3,000 gal/h plant as he can one processing 300 gal. I think also we can claim that equipment generally is becoming more reliable and the necessity to have duplicate or triplicate lines to guard against possible breakdown is receding. Nevertheless, one must always bear in mind the advisability of keeping equipment suffi- ciently flexible to take care of fluctuating intake, and larger units involve more transport. Maybe the very high figures I have quoted are not really practical and the balance between the various factors may result in considerably lower figures.

PROCESSING DEVELOPMENTS Homogenization We can certainly record a rapid increase in homo- genization. In America, of course, the proportion of homogenized milk is already very high, but there is a definite increase in the United Kingdom and in other parts of the Commonwealth, and also in many of the countries in Europe. What are the reasons for this? We know homogenized milk does give a lower curd tension and better digestibility, but 1 think a more cogent reason is the increased use of paper containers, because not only does paper make creamline unnecessary, but it is indeed a disadvantage as the fat tends to stick to the paper and be wasted. Also there are important advantages when milk is being dispensed from bulk in cafes, tea-shops and public institutions. While the stan- dard type of machine is based on the 3 or 5 cylinder high-pressure piston pump, I think I should mention two interesting developments.

The first is the possibility of homogenizing milk by supersonic waves by pumping the milk past a vibrating reed. At present I believe this method is only applied on a batch principle, but there is no basic reason why it should not operate on a con- tinuous flow system. The second development is the modification of a centrifugal clarifier so as to give an homogenizing effect in addition to cleaning: while this may not as yet be capable of such high homogenizing efficiencies, nevertheless it is an extremely interesting development, particularly as it carries out two processes in one machine.

I can trace little change in the methods of cleaning milk in the processing dairy, and both the clarifier and the cloth filter are still in general use. One comment 1 can make, however, is that in general there is much less need for efficient cleaning of the milk in the dairy on account of the very great

improvement in standards of clean milk production on the farm.

Heat-treatment So far as heat-treatment is concerned, I think the first important point to record is the general tendency to increase process temperatures. I n the United States today processing temperatures of 170-180°F are quite common, and the reasons are not far to seek. In the first place, a high proportion of the milk is homogenized and, secondly, a high proportion is packed in paper where no creamline is desired. The opinion is widely held that these higher temperatures improve keeping quality.

Apart from this, the treatment of milk at tempera- tures well above the boiling point is becoming increasingly common. The experimental use of temperatures of 240-280°F arose some years ago when attempts were being made to eliminate the highly resistant organism responsible for the defect in sterilized milk known as 'bittiness'. It was found that although this organism resisted the temperatures of in-bottle sterilization, it could be destroyed by temperatures in excess of 250°F.

Pre-sterilizers are then commonlyemployed ahead of in-bottle sterilizing equipment. Ultra-high tem- perature treatment, as it is called, is now established in its own right and there are many plants operating successfully on this system and producing milk which is virtually sterile.

So much for heating indirectly by plates or tubes. Milk, however, can also be heated by the direct injection of steam, and I propose to deal with this in some detail as plant based on it is now being offered quite widely. Milk can be heated by steam in one of two ways; the first is by the use of a type of injector in which steam passes through a central nozzleand draws in milk round the periphery so that there is a close mixture and high tempera- tures can be achieved. This method is cheap and neat and takes up very little space. On the other hand, there might be a risk of local overheating which might even result in some caramelization, and the problem of accurate temperature control is rather difficult.

The other method is to employ a pressure tank into which milk is pumped under pressure and which contains steam at a pressure corresponding to the temperature to which it is desired to heat the milk. This is much more expensive, it is rather bulky, but it does give very good temperature control, and there is no risk of overheating.

There are legal objections to the dilution wl.ich inevitably results from heating milk by steam, and while I am often in sympathy with those who say that if regulations retard progress then change the regulations, nevertheless, I think it is important to be careful that in doing so one should not permit abuses to occur which the regulation was specifically designed to prevent.

Journal of‘th2 Society . . of Dairv Technology, Vol. 16, No. 2. 1963 I03

Regenerative heat-saving can be applied between incoming raw milk and the heated milk, and it is common practice to achieve final cooling by means of vacuum. This has the additional advantage that water corresponding to that added is boiled off. This process, for example, is now permitted in the United States, provided the milk is cooled by vacuum to a degree or two below the incoming temperature.

The next problem is that of obtaining what is known as ‘culinary steam’ or steam which will not add toxic or offensive substances to the product. I t is common practice in the production of steam to add boiler compounds partly to prevent the formation of scale on the tubes of the boiler, and partly to destroy the oxygen and COr which, at the high temperatures prevailing, are liable to cause corrosion. These substances can be alkalis, tannins, phosphates, chromates, amines and other reducing agents. There is always a danger that a boiler may be overtaxed or suffer a sudden demand of steam, and it might then ‘prime’ or allow actual drops of liquid to boil over together with the steam so it is quite possible for these substances to contaminate the milk. While many are certainly not toxic, nevertheless they may well affect the flavour and quality of the product. A method of avoiding this is by the provision of a secondary boiler in which pure tap water is turned into steam by high pressure steam from the boiler installation.

This brings me to the question of the de-aeration of fluid milk which I must admit 1 find extremely puzzling. Not how to de-aerate the milk-the process itself is comparatively easy to carry out- but the question is whether it really offers any benefit apart from those areas in the world where the milk is contaminated by off-flavours derived from feed or weeds. Another claim is that if oxygen is removed from the milk there is less danger of rancidity.

In my view one thing is clear, and that is to apply vacuum to the milk below the corresponding boiling temperature achieves very little, and in order to carry out effective de-aeration i t is necessary to apply vacuum so that the liquid actually boils or,

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better still, to use a column in which the product can be steam distilled. Whether this process is justified in areas where there is no material feed flavour I think rather questionable.

Automatic control My last point is in connection with mechanical cleaning and automatic control generally. We are now witnessing many advances in this field, and I want to make it quite clear that there are three separate steps in our march towards fully automated operations. Cleaning by the pump circulation of detergent is comparatively simple and can be man- ually controlled. It eliminates the labour ofdismant- ling and re-assembling, and leaves only the necessity for periodical inspection.

The next step is to apply automatic control to temperature, flow, pressure and other variables, and in this way it is still necessary to set the instru- ments manually. The third and final stage is the application of process timing to both the treat- ment of the product and also the cleaning cycle. Here the actual temperatures, flows and pressures are pre-set on a chart and the time factor is also introduced so that once the process is started all factors are automatically controlled until the end of the run.

To sum up, it seems that soon we shall forget entirely the word ‘pasteurization’; we shall be using one of a number of processes, each of which can produce a virtually sterile product and which can offer keeping quality which can be measured in weeks or months. The one obstacle to the wide- spread adoption of sterile milk is, of course, the fact that so far we cannot f i l l it into bottles under completely aseptic conditions, but this is a problem which I am sure will be solved within the next year or two. Already a plant has been operating suc- cessfully in Switzerland filling milk into a paper carton under sterile conditions.

1 think it seems likely that processing of fluid milk will become more of a controlled industrial operation operated on a five- or six-day week, and the adoption of modern process timing methods seems inevitable.

ERRATUM

We apologize to the North Western Section and to Miss N. Bennion for the error which occurred in the History of’ the North Western Section, 16, 44. col. I , lines 17-22 which should read:

‘Many founder members of the Society were active in the formation of the Section including Sir Thomas Peacock, Mr. Edgar Heald, Mr. E. C. Hemming, Mr. G . Walworth-all un- fortunately no longer with us-and Miss N. Bennion . . .’