Chapter 2: Curd[edit | edit source]
There are two phases of the cutting of the curd. The first phase consists of inserting the cutting harp into the vat just along its inner edge and beginning to cut the curd in one direction. Each time the opposite end of the vat is reached, a 180 degree turn is made, lifting the harp a bit but not totally removing it from the vat in order not to damage the curd. Upon arriving at the other edge of the vat, the curd is then cut crosswise, that is, at right angles to the previous cutting direction. The same cutting procedure is followed, such that a cries-cross pattern appears in the curd and vertical strips are formed. At this point there is a pause in the cutting and the sectioned curd is left to rest for five minutes, during which time the whey begins to separate from the solids.
Next the second stage of the cutting begins. The vertical strips of curd are turned with the help of plastic plates that are moved by a second worker, and are then cut with the harp which is passed through them in a perpendicular manner. Grains or cubes of curd are formed in this way. The number of passes made depends upon the size of grain desired. In principle, in order to obtain a semi-hard cheese, an attempt is made to cut the curd in grains of 6 to 7 mm in diameter. However in practice, the grain size is between 5 and 10 mm, a variation that is perhaps due to the difficulty of the operation and the inexperience of the cheesemakers. As a general rule, the grains of curd should have a size similar to a mediumsized kernel of corn.
The entire curd cutting process lasts about 10 or 15 minutes. The cutting of the curd must be done with much care, since if it is not cut correctly there will be many losses due to the pulverization of the grains (grains cut too small) and to the separation of fat, which, upon mixing with the whey, changes the latter from an almost transparent yellowgreen to a whitish colour. These problems will reduce the yield of the conversion of milk to cheese.
An easy way to gauge the size of the curds.
|Type of cheese||Size of curd required|
|Fresh||up to 2 cm in diameter|
|Andean (soft)||lima bean (1.5 cm)|
|Tilsit (semi-hard)||maize grain (1 cm)|
|Gruyere (hard)||wheat/rice grain(0.5 cm)|
Stirring, or agitating the curds (Photo 3), separates them from the warm whey and causes them to shrink and increase in density as a result of the whey loss. For hard cheeses, the major part of the whey must be removed from within the grains of curd or the cheese will be too moist and, as excess moisture and excess lactose favour the multiplication of microbes, it will not have a long shelf life.
Stirring should gradually quicken so that grains of curd move swiftly along the surface of the whey. The time required for stirring varies according to the type of cheese being made: curds for soft cheese, which requires large grains with a high moisture content, should not be stirred for long, while those for semi-hard and hard cheeses should be stirred for longer, to produce small grains with a low moisture content.
Increased levels of acidity and temperatures facilitate the construction of the curd grains. If the milk is very acid, or stirred at too high a temperature, then the curd will be too hard and the stirring will have to be accelerated.
Removal of whey
After stirring has stopped, the grains of curd sink to the bottom of the vat because of their greater density and the whey can be removed. Occasionally, however, curds will float, usually due to the presence of carbon dioxide from coliform contaminations. The whey is skimmed from the vat with a plastic or stainless bucket, changing the position of the bucket so that the mat of curd at the bottom of the vat is not pressed in the same spot. Normally about 30 per cent of whey is removed; more, if acidity is more than 13 Dornic. Whey can be removed from the base of a vat if a suitable drain-lock and sieve are used.
Washing and salting
Washing the curds by adding and stirring warm water enables the removal of the remaining lactose and lactic acid, and adds water. This is suitable only for the washed-curd types of cheese, such as Swiss and Dutch cheeses. The addition of salt during washing helps prevent the growth of microbes and gives the cheese a longer shelf life.
Certain cheeses Tilsit and Danbo, for example need hot water (65 to 75 C). In these cases it is very important that the water is added slowly and steadily while the curds are being stirred. This process should take five to ten minutes. If not done correctly, the curds will form hard crusts and retain moisture instead of expelling it.
While the water is being added, the curds must be stirred continually. This stirring continues for a specific period of time, depending on the type of cheese. Very soft cheeses, for example, need only 10 minutes from the moment the water is first added. A semi-hard cheese (Tilsit, Danbo) needs about 30 minutes of stirring in all. A very hard cheese (Gruyere, Parmesan) needs 60 to 80 minutes. During this process, the whey is expelled from the curds. Most of the whey is then removed with plastic dippers to facilitate gathering the curds for the subsequent moulding.
Moulding and Pressing
To shape the cheeses, the curds are packed into moulds. The moulding table is covered with a thick nylon mesh (2 mm squares). The moulds are placed on top of this mesh so that the cheeses may acquire a pleasing grid pattern on the outside. While one person stirs the curds, another scoops them out and pours them into the moulds, until they are full (Photos 4 and 5). The whey drains out through the holes in the sides of the moulds and base. Drainage can be speeded up by lightly pressing down on the curds with the hands. In about five minutes, all the visible whey will have been drained and a compact mass will have formed. The cheeses are then ready to be turned over for the first time. The subsequent pressing process depends on the type of cheese.
Soft cheeses, made from large curds, are not pressed because they would lose too much humidity. After the curds have been placed in the moulds, their own weight provides sufficient pressure to form the cheeses. The correct room temperature is absolutely essential for this process: it must be warm, with 20 C being the optimal temperature to allow the specific bacteria to grow and produce the correct acidity. This acidity in turn allows the whey to drain off, without any extra pressure. To maintain the 20 C temperature, the doors of the moulding room must be kept closed. The run-off beneath the moulds should be rinsed away with the warm whey (never with cold water) to avoid an abrupt drop in temperature. In high altitudes and colder climates, the moulding cheeses must be covered with a large piece of plastic to keep them at 20 C.
Hard and semi-hard cheeses, made from small-and medium-sized curds, are pressed for specific lengths of time depending on the type of cheese. Each cheese in its mould is wrapped in a cloth, with the edges folded up smoothly over the top. A piece of wood, shaped to fit into the mould, is placed on top of the cloth. A round piece of cement, made to fit into the mould, is placed on top of the wood. Generally, 4 kg of weight are needed for Andean cheese, 6 kg for Tilsit, and 10 for Danbo. Danbo cheese is made in a rectangular mould with rectangular weights.
The cheeses are removed from the moulds after a half an hour. The cloths are wrung out to remove the whey and any dry crusts that have formed around the edges of the cheeses are cut off. The cheeses are turned upside down and placed back into the moulds. They are then rewrapped (called 'dressing') in the cloth and weighed down again for another hour, then unwrapped, unmoulded, and turned over again. Next, the cheeses are returned to the moulds and placed on a dry cloth, unwrapped. They are left sitting until the next day (approximately 12 to 14 hours). During this entire process, an effort must be made to keep the room temperature as close to 20 C as possible. An experienced cheesemaker will, at this point, have a good idea how successful the fermentation process has been. The cheese should be yellow, with a firm texture, and the top edges should have pulled away slightly from the mould. A poorly processed cheese will be pale, with a mounded top and its edges touching the mould all the way around. This can result from the presence of coliforms or any gas-producing micro-organism; even reactivation of the starter culture can cause gas formation. These cheeses will swell to form bloated balls and the only way to save them is to process them immediately into Mozzarella or Provolone (see p.44). It is very important for the cheesemaker to realize that coliform gassy fermentation is a serious problem and s/he must recheck the entire process used, including milk quality, culture and general hygiene procedures.
The moulding of Gruyere cheese is a difficult operation. A thin steel strip is fitted on the edge of a coarse-woven dipping cloth, overlapping slightly. The steel-edged cloth is passed down and under the curd bed in one smooth swoop. The four corners of the dipping cloth are brought together to form a bag, and the filled bag of curd is pulled out of the whey, then deposited directly into a round, wooden Gruyere cheese hoop. Remove the small amount of curd left in the bottom of the vat and quickly return it to the curd bed. Fold over the heavy cloth and knead the cheese lightly with the palms of the hands.
A Gruyere cheese, which is very large, needs a great deal of pressure about 10 times its own weight. The pressing should be gradual: a little pressure at first, then slowly increase the weight. If the pressure is too heavy at the beginning, while the cheese still has a lot of whey, a thick crust will form around the entire cheese, preventing the rest of the whey from draining out. The end result will be a cheese with a hard, dry outer layer and a white spongy acidic inner layer, with drops of whey. As it continues to mature, the flavour will become bitter.
To facilitate whey separation from curd:
Â· The temperature should be 31 to 33 C
Â· Add more rennet to reduce coagulation time
Â· Prevent too rapid acidification, avoid milk that is overripe or too much culture
Â· Cut the curd earlier
Â· Cut the curd into finer (rice-sized) grains
Â· Increase stirring to two hours
Â· Increase temperature during stirring to 55 C (for Parmesan)
Â· Turn the cheese more frequently in the moulds.
To slow down the whey separation from curd:
Â· Use pasteurized milk
Â· Raise temperatures for coagulation (35 C in Andean or lower in Camembert, 26 to 29 C)
Â· Cut the curd after it has become well stiffened
Â· Cut the grains larger
Â· Stir slowly for a shorter time
Â· Increase the temperature of the hot water used during the second stirring to form a hard surface that will prevent the escape of whey
Â· Salt the curd.
After 24 hours remove the cheese from the mould, weigh it to calculate the conversion from milk into cheese and identify each cheese clearly with the date of its pressing.
The conversion or yield from milk to cheese varies considerably, but depends to a large degree on the fat and protein content of the milk, the quantity of fat lost during cheesemaking and the amount of water absorbed during the stiffening process (see Figure 12 and Table). Other factors also play a part; in Europe, for example, the yield from autumn milk is higher than from spring milk due to the higher protein content of the former and its mineral balance (see also p.14). A high conversion cheese one which requires less milk for the same quantity of cheese will be cheaper to produce and more cost-effective than a low conversion cheese. Conversion may be expressed either as the quantity of milk required to produce 1 kg of cheese or by the number of kilograms of cheese obtained from 100 litres of milk:
Yield of cheese from milk.
|No. of litres of milk required for 1 kg cheese||No. of kg of cheese produced from 100 litres milk|
|Mozzarella (fresh Provolone)||10.5||9.5|
Figure 12. Relative composition of milk and cheese
Relative composition of milk, soft cheese and hard cheese.
|Milk||Soft cheese||Hard cheese|
|Fats||40 g||240 g||315 g|
|Protein||35 g||205 g||275 g|
|Carbohydrate||48 g||25 g||25 g|
|Mineral Salts||7 g||20 g||25 g|
|Water||870 g||500 g||350 g|
|Salt||10 g||10 g|
Brine, a known solution of salt in water, forms the cheese rind. The salt solution hardens the outer layer of the cheese by drawing off the moisture from the surface of the cheese. The final texture of the rind depends on the salinity, acidity and temperature of the brine: too little salt will not draw off enough moisture and the rind will not be properly hardened. Too much acidity will damage both the rind and the cheese during ageing, and if the brine is too cold then there will be insufficient exchange of whey and salt and the rind will be soft.
Boil 30 litres of water and, while it is still hot, dissolve in it 10 kg of salt. This gives a salinity of about 20 to 22 C Baume. Cool the brine to 12 C before submerging the cheese. Salt may be sprinkled on the upper side of the cheese to obtain uniformity.
Cheese is left in the brine (Photo 6) according to its size, for example: Andean cheese (1.2 kg) requires 6 to 8 hours, Tilsit (3 kg) 20 to 24 hours and large Gruyere (40 kg) 48 hours.
The salinity of the brine gradually decreases and its acidity increases. When the acidity rises above 40 D the brine should be discarded. When the salinity falls below 18 Baume, salt should be added until it reaches its original salinity. The temperature of the brine must also be checked from time to time and should vary between 8 and 12 C. After brining, remove the cheese, allow it to dry a little and place it on the lower shelves in the maturing room so that it does not drip on to older cheeses.
Chapter 3: Cheese[edit | edit source]
Maturation, also known as ripening or curing, results in some instances from the growth and multiplication of aerobic microbes on the rind, progressing inward after a few weeks, and produces a well-ripened cheese with a pleasant aroma, flavour and texture. Enzymes, produced by B. Liners bacteria in particular, pass into the cheese mass, contributing to the aging process, and are especially important in the formation of taste and aroma. Not all cheeses rely on microbes entering from the rind the starter culture microbes or their enzymes will be present throughout the cheese.
Changes in cheese during ripening
Growth of bacteria. Rapid growth takes place during the first few days of the ripening period. One or two grams of three-day-old cheese may contain several hundred million bacteria.
Change in the types of bacteria. During the first few days the streptococcus organisms, chiefly from the starter, are in the majority. Later, lactobacilli and others, like propionic bacteria (in Swiss cheese), predominate. (See Figure 13).
Figure 13. Normal bacterial contamination
Decrease in sugar content. The remaining lactose present usually disappears in the cheese within a few days.
Decrease in moisture. There is a slow decrease in the percentage of moisture, even in paraffined cheese.
Decrease in acidity. There is a decrease in total acidity as the ripening progresses.
Change in pH. The pH is lowest (most acid) in the cheese about the third or fourth day after moulding. It then increases slowly during the ripening period. A pH level of 5 to 5.2 of cheese after pressing will rise to 5.4 to 6 after four weeks and 5.8 to 6 after eight weeks. If, however, the pH level drops, the cheese will have a sour or bitter flavour.
Change in the flavour. Good quality cheese kept at 15 C should develop a pleasant, full flavour in four to eight weeks. Certain volatile flavouring compounds are formed.
Change in the body of the cheese. The chemical and physical properties of the casein change as the ripening progresses. Increasing amounts of casein are changed to a more soluble form by the action of bacteria and enzymes. The change is accelerated at higher ripening temperatures. The body of a good cheese changes from a tough corkylike texture to a smooth, waxy consistency. In acid cheese a mealy, pasty body results.
Production of gas. Gas production is normal in some cheese. It is, of course, abundant if the cheese contains the typical gas-producing bacteria, as with Swiss cheeses.
The temperature, relative humidity and ventilation in the maturing rooms where the cheeses remain until their sale all affect the maturation of the cheese. Ideally, the room should be ventilated, but the air should have a relative humidity of about 80 to 90 per cent and the temperature should be between 13 and 15 C. If too low a temperature is used, the cheeses will mature very slowly and may have an acid flavour and a crumbly texture; if too warm, the cheeses will become soft and break down. If the humidity is too low the cheeses dry out, become very hard and will crack; too high and they may become covered with a foulsmelling yellow-white scum. A thermo-hygrometer measures both temperature and relative humidity accurately, but it is sufficient to measure only the temperature daily. The approximate relative humidity can be estimated by inspecting the cheeses, an ability that comes with experience. Dry, cracked cheese indicates a low humidity and yellow surface scum indicates high humidity.
Temperature and humidity can be manipulated in various ways. The room temperature can be raised by opening the door to the production room where the vat is being heated and can be cooled by adding a ceiling or a second roof to prevent direct sunlight or by opening windows at night. Cover the window opening with a fine mesh to prevent insects and other pests from entering. A dry curing room can be made more humid by spraying the walls and floor with water daily, taking care not to wet the cheeses, and by keeping doors and vents closed to prevent the escape of moist air. A more expensive solution is to add pools of water or pipes which wet the walls when necessary. Opening windows and doors might dry out a damp curing room, but in very damp climates it is sometimes necessary to put in moisture-absorbing substances such as sawdust or sand.
As the cheese is initially very acid, the lactose having been transformed into lactic acid, bacteria will preferentially grow on the rind. A cheese left unattended in the maturing room will soon become covered with a layer of mould and decay. Wiping the cheeses gently with a moist cloth not only reduces mould formation but can also inoculate a new rind with bacteria from old rind, thereby helping the rind to develop and encouraging the maturation from the surface to the inside of the mass. Smearing a liquid bacterial culture on the surface also protects against mould.
Wiping is done in two stages:
1. Wipe the sides and upper face of the cheese with a moist cloth, keeping the shelf dry.
2. Two days later turn the cheese over and wipe the other face and the sides.
Smoked Provolone belongs to the 'pasta filata' or stretched curd category of cheeses traditionally produced in Italy, Bulgaria, Rumania and Turkey. It is related to Caciocavallo and Mozzarella. It is made from fresh milk, raw or pasteurized, though slightly sour milk can be used. Bacterial starters are added to achieve a specific level of acidity and curds are formed by the coagulating action of rennet. Andean cheese, Tilsit and Danbo are all made in a similar way. However, for Provolone, instead of moulding, the curds are piled onto a table and left to ferment. After fermentation, the curds are cut and heated in water and then stretched and rolled into round, pear-like or sausage shapes. The weight can vary from 450 to 2,270 g. The cheeses are hung in plastic or string nets during the subsequent drying and ripening. The outside has a shiny surface, smooth and well-sealed, without cracks or holes. After hanging the cheese turns yellow and is then ready to be smoked, if required, which imparts the characteristic pleasant smokey aroma of this popular cheese.
Raw material and acidity test
Smoked Provolone is made from curd which has fermented over a 15-to 30-hour period at 20 C. The acidity of the curd is the decisive factor in forming smooth and well-shaped cheeses. In hot weather, 15 hours of fermentation is enough, whereas in cooler periods, up to 30 hours are needed.
A simple test after fermentation determines the correct acidity and therefore the right moment to begin stretching and moulding: take a one cm strip of curd and submerge it in water (65 C) for two minutes. Remove it and stretch it. If it stretches smoothly to approximately double its length, it is ready. If not, or if it breaks, it needs to ferment longer to increase the acidity. If the curds are not acid enough the curd will be lumpy. On the other hand, if the curd stretches very quickly and is very soft it has overfermented and the strings will break and not hold together during shaping.
In rural cheese factories, Provolone has been successfully produced from curds which had been intended for Danbo/Tilsit or Andean cheese, but which had suffered from coliform gas fermentation and were therefore disqualified from the ripening process. These cheeses have to be processed within a maximum of 40 hours after moulding.
When the curds are ready to be stretched, cut them with a large knife into narrow strips, not more than one cm wide.
Heat a large (50 litre) pan with 20 litres of water to 80 C. Add about 20 kg of the strips of curd to the water, making sure that all the curd is covered by water. Leave the curds submerged for 5 to 10 minutes, allowing the water temperature to drop to 65 C. Using a large wooden paddle, begin stretching the curds with a pulling movement. Continue until a smooth, uniform, white plastic mass forms. At this point, place the paddle under the curds and lift them out, letting the mass fall on either side of the paddle. Pull out a segment of the mass with both hands, pulling, stretching and squeezing it, and smoothing out holes, lumps, rough parts, drops of water or whey (Photos 7 and 8). Then let it fall back into the water and begin again with another segment. If the curds have not been well worked, they retain a great deal of whey, which is discarded during the ripening process, leaving folds in the surface of the cheese.
During this entire process, the temperature of the water and the curds must remain at between 60 and 65 C.
When the mass of curd is shiny and of a uniform consistency, pull a segment and begin to roll the curds up into a very tight shape, rotating the ball until it reaches the desired size. This must be done by pulling firmly and steadily on the curds so that each thin layer will join the one beneath. If this is not done properly, air pockets and whey will be trapped between the layers of the cheese and create an imperfect product. When fully formed, the hot ball of cheese is placed in the middle of a piece of thin cloth, 50 cm square. The cloth is folded lengthwise over the cheese and its ends are twisted in opposite directions, compressing the cheese and removing the last drops of whey.
Cooling and brine solution
The cheese is removed from the cloth and tossed into a cold water-bath to cool. The bath must be kept constantly cold by a flow of running water. After approximately two to four hours the cheeses are removed from the cold water-bath and placed in a brine solution (20 to 22 Baume) for four to six hours, according to their size. The brine solution is prepared by adding 10 kg of industrial salt to 30 litres of boiled water. Since the cheeses float, extra salt must be sprinkled on top to obtain uniform salinity.
Drying and weighing
After the salt bath, the cheeses are placed in a net bag made from either plastic or string. They are tied together in pairs and hung over a stick for three to five days to dry (Photo 9). Once dry, all the cheeses from the same batch are weighed together to determine the yield produced from the fresh milk.
Smoking gives the cheese its characteristic golden colour and appealing aroma and flavour. It also acts as a germicide on the surface of the cheese. It is important that the smoke does not heat the cheese directly. An effective design, therefore, is to produce the smoke away from the smoking room, so that only the cool smoke reaches the cheeses (Photo 10). When the fire is burning well, sawdust is added to produce copious amounts of smoke. Smoking takes four to eight hours, depending on the intensity of the smoke, until the cheeses are shiny and golden coloured. Care must be taken to select wood from a safe source; industrial cuts are unsuitable, for instance.
The yield of Provolone cheese is less than other types of cheese, since part of the milk fat is not incorporated into the curds, but is lost in the water bath. Ten and a half to eleven litres of milk are needed to obtain 1 kg of Provolone cheese.
The smoking process further if educes the weight of the cheese by 10 per cent. If this yield is not obtained, too much milk fat has been lost in the water bath, either because of low acidification of the curds or overlong submersion in the hot-water bath.
Ripening and preservation
Smoked Provolone cheese can be consumed immediately after smoking, when the smoky flavour is most prominent. It can also be preserved for several weeks, which hardens and ripens the cheese. The ideal conditions for ripening consist of a 14 to 16 C temperature and an 80 per cent humidity. However, in the tropics, Provolone has been successfully ripened at 20 C and 95 per cent humidity.
Undesirable bacterial growth seldom presents problems during the ripening process, due to the high acidification and temperature of the curds during stretching. This process destroys the majority of microorganisms and inhibits the development of surviving bacteria.
The main problems are external, such as fly larvae on the surface of the cheese. Ants and cockroaches have also been known to descend the strips. Moulds can grow, too, when there is excessive humidity. In this case, the cheeses must be cleaned with a dry cloth.
To avoid these problems, and to conserve the moisture in the cheese, the cheeses can be wiped with vegetable oil or with a plastic solution (Mowilith or Foodplast) which also improves their external appearance. As the cheese ripens, the acidic taste is replaced by a sharp, highly aromatic flavour and the texture becomes firmer and drier. Occasionally 'eyes' will appear in the body of the cheese, due to gaseous fermentations.
Use of the by-products
The whey or water mixture left after the stretching of the cheese is rich in fat. It can be passed through a cream separator, or just left to set overnight and the resulting fat can be skimmed off and made into butter.
Disadvantages of Provolone cheese
- The processing is slightly difficult at first, until one becomes accustomed to judging the correct moment to begin the stretching and pulling.
- The temperature of the curds is quite high and takes getting used to.
- The yield is low, which causes the price of the cheese to be higher than other cheeses.
Mozzarella is a soft, white cheese, similar to Provolone, but with a higher whey content and is sold fresh. It is packed in plastic bags and needs to be refrigerated for not more than about 10 days. Consumers prefer lowfat Mozzarella (30 per cent fat) for dietetic purposes. It is often used as a pizza topping, since it forms the characteristic long strands when heated.
The production of Mozzarella is the same as that for Provolone until the curds are about to be stretched. Then they are worked only half as long as the time taken for the Provolone curds, leaving more whey in the curds. They are stretched and rolled into firm balls, as with Provolone, but instead of being squeezed in the cloths and put into cold water they are immediately put into plastic bags and sealed. They are put next to one another on shelves, in a cold room (4 C), to be delivered as soon as they are cool, (normally the next day). Mozzarella can also be dried in a cold room without the plastic bags, producing a firm texture which is easier to slice, often preferred by Pizzerias.
The yield of wet Mozzarella is 1 kg per 10.5 litres of milk with three per cent butterfat.
Preserving and record keeping
A well-made cheese will last for a long time. Nevertheless, some factories add sodium or potassium nitrate to the milk to prevent the swelling up of the cheese caused by cold or butyric bacteria. These additives are not always successful however: active aerobic cold bacteria in milk, for example, prevent potassium nitrate from working and can produce a bitter taste in the cheese, lowering its quality. It is better to eliminate the need for preservatives by ensuring that good hygiene prevails at all times.
A record (see Figure 14) of daily procedures can help analyse and understood successful and unsuccessful batches. The record should include all the items given in the box.
Figure 14. Example of record keeping
Common problems and their causes
Cheese with cracks
Over-acidified milk or carelessness with starters and production can result in too much whey remaining in the cheese. During secondary maturation, the necessary enzymes will be unable to penetrate the cheese from the rind to the centre, often producing a cheese with two colours, which is ripe on the outside but bitter and crumbly within. Specific causes can be one or more of the following:
- Undue care at milking
- Milk exposed to sunlight (that is, heat) resulting in high acidity
- Dirty milk churns
- Negligence and delays in manufacture
|Daily technical report 1. date
2. quantity of milk in vat 3. type of cheese to be made 4. quantity of fat in the milk 5. acid level of milk 6. type and quantity of culture and amount of rennet used 7. temperature of coagulation 8. time in minutes of cutting and stirring 9. size of curds 10. acidity of whey 11. amount of whey extracted 12. amount of water added 13. amount of salt added 14. time in minutes for washing and stirring 15. temperature of whey after final watering 16. total time of preparation from rennet to pressing 17. number of moulds 18. weight of new cheese before brine bath 19. weight of cheese after maturation 20. conversion of milk to cheese 21. observations
Early blow-ups (Pressler defect)
Blow-ups, where the cheese becomes full of small or large bubbles of gas, can occur during pressing (called the Pressler defect). They are normally caused by Aerobacter aerogenes or Escherichia cold entering the milk during milking or transport or through cloths or cloth filters and are invariably due to a lack of hygiene, such as:
- Unhygienic milking or dirty cloths
- Dirty churns
- Milk containing antibiotics or other inhibiting substances (mastitis, for example) which sets back growth of the desired bacteria.
- Degenerated cultures
- Dirty water
- Unhygienic workers.
Blow-ups can be prevented if the level of milk contamination is slight with an active culture of streptococcus, but nothing can prevent the growth of coliforms if milk is contaminated by antibiotics.
Clostridia are mobile, anaerobic and spore-forming microbes. They are present in large quantities in faeces and produce large quantities of carbon dioxide and hydrogen gas and cannot be eliminated by pasteurization. These bacteria enter the milk from the hands or clothing of personnel or when tiny bits of excrement fall into churns and milking equipment. Care must be taken to avoid, in particular:
- Unhygienic milking near manure and muck
- Rotten silage for feed.
The only defence is to prevent the bacteria entering the milk and the importance of good hygiene cannot be overemphasized.
Figure 15. Late blow ups