In this article we will discuss about:- 1. Introduction to Continuous Cheese Making 2. Basic Principles of Continuous Cheese Making 3. Methods 4. Advantages.
Introduction to Continuous Cheese Making:
It is generally agreed that the conventional batch process of cheese making is time-consuming and laborious, involving back-breaking manual work. Further, the rise in present- day labour and manufacturing costs in cheese making countries has made it necessary to look for ways of mechanizing cheese making.
A study of the time-schedule adopted for making cheddar cheese from pasteurized ripened milk will show that the total time required from receiving milk to first pressing is about 6¾ hours, with the following break-up-
Although in the process itself there has been little change in the last century, a considerable amount of mechanization has been successfully introduced in all phases of cheese-making operations over the past thirty years.
Since 1950, much progress has been made in the mechanization of the manufacturing process of several varieties of cheese, and more recently, continuous methods have been introduced. Continuous cheese-making, as distinct from the conventional batch method, implies a steady and continuous treatment of the curd to expel whey until a ‘green’ cheese or filled mould is obtained.
Basic Principles of Continuous Cheese Making:
The cheddar cheese-making process can be divided into 4 phases, which can most rationally be mechanized and automated along the following lines:
Phase I- Setting, Cutting and Cooking:
This begins with the addition of starter to the milk in the vat and extends to the removal of the bulk of the whey from the curd. In the batch method, this phase is carried out in rectangular jacketed vats which are equipped with mechanically-driven agitators and can be heated by injection of steam into the jacket.
The cheese maker cuts the curd, operates the agitators and the steam valves, determines the titratable acidity of the whey at intervals, and at the required acidity, first draws off a half and later all the remaining free whey.
The above operation has been considerably mechanized and can be automated by equipping the vats with temperature and pH regulating devices. An important approach to improving this phase has been continuous precipitation of curd using cold renneted whole milk (Berrige—U.K.; NIZO/Nicoma-Netherlands) and cold renneted concentrate (Stenne-Hutin-French).
Although there have been some commercial applications of these processes to soft cheese, the same is not yet true for hard pressed cheeses. Until this is done, the best approach seems to be to automate deep round-ended horizontal vats and pump the curd and whey to a suitable continuous cheddaring system.
Phase II- Drying and Cheddaring Curd:
This could be mechanized by a machine that would convert the granular curd into a fibrous slab. This stage is a laborious one when carried out in the vat and mechanization will reduce the back-breaking work involved. There have been a number of approaches to mechanizing the cheddaring of cheese and these can be classified as- Cheddar Towers; Batch cheddaring or Cheddar-box systems; and Continuous cheddaring.
In cheddar towers (developed by NIRD in the U.K.), the normal 17 curd is placed in an elongated vertical cylinder tapered at the top with its upper portion perforated to facilitate whey drainage. The curd is forced downwards by the pressure of the succeeding curd. As it progresses down the enlarging cylinder, it expands or flows and produces the stretch required for a desirable cheddar texture.
The matted curd is removed by a cutter that cuts off layers from the bottom. In the cheddar-box system (developed in Australia, New Zealand and the Netherlands), the traditional batch method of cheddaring, i.e., the formation of curd blocks with regular turning to allow for curd flow, is initiated in a machine and the whole period takes at least one-and-a-half hours.
In the continuous cheddaring system (developed in the U.S.A. and Australia), the curd and whey are pumped to a vibrating screen for separation. The curd falls into a vertical curd-fusing section where some further drainage takes place and it mats together. At the bottom of the fusing section, the curd flows on to a cheddaring belt and is slowly moved in a continuous stream to the curd mill.
Phase III- Milling, Salting and Hooping:
This needs large amounts of labour by traditional methods, involving strenuous manual work. Mechanization would not only reduce the labour force, but also take a shorter time and increase efficiency. The operation is better performed away from the coagulation vat. With modern milling machines, the curd is not damaged much and fat losses are reduced.
There is no manual handling of the curd after it is placed inside the curd mill; this reduces the possible pick-up of coliforms and other undesirable organisms and extraneous matter. The accuracy of mechanical salting is better than that obtained by hand salting. The filling of curd into hoops has been considerable mechanized, as also the operations of cheese washing, drying, brine salting and waxing.
Phase IV- Pressing and Packaging:
This stage of the cheese manufacturing operation uses the largest percentage (nearly 40 per cent) of the total cheese labour requirements and, therefore, its mechanization should receive much more attention in the future than it has done in the past.
It could be dealt with under the following headings:
1. Rectangular film wrapped cheese;
2. Brine salted cheese;
3. Large block pressing;
4. Continuous pressing and extrusion;
5. Continuous pre-pressing of 40 or 60 lb. blocks;
6. Vacuum pressing.
There has been a gradual change from round blocks to rectangular ones all over the world; the latter can be film-wrapped conveniently by machine, thereby much reducing packaging costs. Mechanized brine salting reduces labour costs considerably. Several countries have adopted large block pressing in an endeavour to reduce capital and labour costs.
The continuous pressing and extrusion of cheese, and continuous pre-pressing of 40 or 60 lb. blocks are both time- saving processes. Vacuum pressing is catching on all over the world, since it caters principally to the demand for close-textured cheese by consumers in their cut and wrapped pieces. Considerable work has been done in the mechanization of the cheese mould and hoop handling from the filling point to the packing room.
Methods of Continuous Cheese Making:
With the development of the ‘short-time process’ of cheddar cheese-making by adding more starter, or by increased syneresis or the drying off of curd, there has been greater scope for large-scale mechanization. A great deal of intensive research in this regard has been carried out in Australia, New Zealand, U.K. and the U.S.A.
One method of continuous cheese-making developed in each of the above countries is briefly described below:
(i) CSIRO (Australia):
The latest cheese making and cheddaring unit has been called the ‘Bell-Siro Cheese maker 2, Mark 2’, while the milling, salting and hooping unit is known as the ‘Eell-Siro Cheese maker 3’. The Cheese maker 2, Mark 2 is capable of handling between 6000-10,000 lb. of curd an hour.
The curd and whey mixture is pumped on to a rotating perforated cylinder to separate the curd, which moves along an endless belt on which it is compressed. The compacted curd is sliced and deposited into cheddaring boxes. After cheddaring, the blocks are automatically transferred into the milling, salting and hooping machines.
(ii) DRI (New Zealand):
Here, the cheese making equipment has been called the Cheese-master. In this, the curd and whey are pumped from the vat to a draining conveyor, which consists of a slow-moving belt with perforated stainless steel slats. Four sets of drums fitted with peg stirrers prevent matting during the draining period.
The drained curd is delivered by gravity into stainless steel cheddaring boxes, each holding 400 lbs of curd which are turned through 90° every 15 minutes. This results in the cheddaring of curd in due course. The large cheddar blocks are milled by a rotary mill and deposited on a belt similar to the one described above. The milled curd is mellowed for 5-10 minutes before it undergoes mechanical salting and hooping.
(iii) NIRD (UK):
The essential feature of this method is cheddaring in a tall vertical tube, which widens towards the bottom and is insulated. Whey drains between the curd and the wall of the tube; or if a perforated tube is used, it goes through the holes and out by a separate outlet. The weight of the curd assists the cheddaring process in all these different methods.
A cutting disc at the bottom supports the curd mass and cuts off slices or chips of curd, which are collected at a controllable rate and passed on for direct salting, as further milling is no longer required. To initiate the process, the tube must be filled with curd. This naturally does not receive the proper cheddaring treatment and must subsequently be handled separately.
When the supply of curd is used up, pressure can conveniently be applied to the last batch by compressed air blown in with the top of the cylinder sealed. It is claimed that in a factory operating 12 vats, the man-hours can be reduced from 48 to 8 at the cheddaring stage.
(iv) Ched-O-Matic (USA):
In this case, the curd is handled normally in regular cheese vats until dipping. Afterwards a curd and whey mixture is pumped into an inclined rotating perforated drum for whey removal. The dried curd is deposited on the top of a large rectangular pressing unit provided with channels to permit the whey to escape. After cheddaring, the curd is cut and milled automatically. The milled curd is mechanically sprayed with brine and conveyed to the hooping device.
Advantages of Continuous Cheese Making:
Continuous cheese-making has the following advantages over the traditional batch method:
(i) It is more economical, since power is usually much cheaper than hired labour;
(ii) Processing is more uniform and should be more reliable, provided mechanical breakdowns can be avoided.