Technical Information

Why doesn't milk set the same way each time I make cheese?

Achieving a good set of your milk is one of the most important steps in making cheese if you want to make good cheese. But it can also be one of the most frustrating. There are several practical considerations that the cheesemaker needs to be aware of that can affect how well the rennet will work when it is added to the milk to make cheese.

Background to forming a cheese curd
A key part of making cheese is forming a curd. A cheese curd can be formed by either the addition or production of acid in the milk, this is an acid set cheese. Yoghurt, Persian feta and some Mozzarella types are good examples of these. The second way a curd can be formed is by the addition of rennet and is called a rennet set curd. The vast majority of cheeses that you will make and eat will come from rennet set curds eg. Cheddar, Camembert, Blue Vein, Gouda and so on.

What is happening when the rennet forms a curd?
Rennet is an enzyme that coagulates the milk, basically it turns the milk from a liquid to a solid. Chymosin is the active enzyme in the rennet that does this. When rennet is added to the milk (see foot note) it needs to be stirred in very well, the milk is then left undisturbed for a predetermined time, usually from 30 – 60 minutes depending on the type of cheese and the recipe. During this time the Chymosin cuts (cleaves) off the casein portion of the protein from the other proteins (whey proteins) in the milk and the caseins then all bond together into a fibrous structure referred to as a gel. The gel grows in strength during the set period. This gel now contains most of the milks components: fat, casein, calcium, starter cultures, some water, and some of the chymosin itself.

What are the Practical considerations for the cheesemaker?
The formation of this gel is when a cheesemaker may experience differences in how well the curd will set. A cheesemaker requires the gel to be a certain strength (referred to as being set) before the curd can be cut and then stirred. If the set is not strong enough at the cut stage, the finished cheese may have inconsistencies and it may turn out as an inferior quality cheese. A curd that is too soft will not drain sufficiently and will make a cheese that is over moist, over acid and with a weak structure. A curd that is over set will produce a cheese that is too firm, too dry and will not ripen adequately. The issue for the cheesemaker is that all milks do not set exactly the same so it is important for the cheesemaker to understand that there are several variables that may affect how well a cheese is going to set. Understanding these variables will assist you with dealing with the problem for the current batch and or future batches of cheese.

  1. Volume of rennet added:
    Only add the required rennet according to the recipe and to form a firm set in the required amount of time. Generally, rennet volumes can be varied up and down just a little bit, and I mean only a little. Adding too much additional rennet may achieve a firm set, but the additional rennet activity within the cheese may produce a weak and pasty body and off flavours in the cheese. This is because the rennet is a proteolytic enzyme that breaks down the cheese structure as the cheese matures. The required amount of rennet should be accurately measured in a clean plastic syringe or small graduated measuring cylinder and stirred into the milk very well.
  2. Temperature of the milk:
    Rennet works best at 40°C ‑43°C, but rennet will work satisfactorily but more slowly at 30°C ‑ 32°C. For example, if using the same milk and the same volume of rennet you will get a better set of the milk at 42°C, by about 5 – 10 minutes, then you would if the same milk was at 32°C. Some recipes use lower temperatures for setting milk because it is the most suitable for temperature for starter growth eg Mesophilic starter cultures are usually required for recipes that use temperatures around 34°C or less.
  3. Acidity of the milk:
    The action of rennet in the milk is assisted by small increases in acidity. The acid ripening of the milk after starter addition has the effect of helping to speed up rennet setting times. For example, if using the same milk but different volumes of starters, the milk with the greater volume of starter culture will set before the milk with less starter culture. But that is not a license to add more starter as this may over acidify the cheese.
  4. Milk from sick cows, cows in late lactation and mastitis affected milk:
    The very slight increase in alkalinity in these milks is enough to impair rennet action. The additional albumin and globulin caused by mastitis infection also retards coagulation. Similarly, the imbalance in the minerals and proteins in the milk of cows that are almost ‘dried off’ may also cause inconsistencies in sets.
  5. Different animals and different breeds
    Cheese has been produced from many animals over the years. The cow and goat mostly but sheep and buffalo are becoming more common in Australia. The milk from each of these species will vary and with that the set of the milk will vary. As a general rule a milk with more Casein and Calcium will have a firmer set curd than a milk with less of these components. Buffalo and sheep milk have significant higher levels of both of these components compared to cow and goat milk. Usually a lot less rennet is used with sheep and buffalo milks.
    Then there are the differences within different breeds of animals for example a Jersey or a Guernsey will have more casein and calcium than a Fresian, so you would expect a jersey milk to set faster and stronger than a Fresian milk.
  6. Different composition of milks at different times of the year
    The composition of the milk between individual animals of the same breed varies, depending upon the influence of factors such as time of year, stage of lactation, availability and type of feed, and udder and general animal health of the animal. Milk is not a constant composition throughout the year and this will influence your sets, but there is not usually a significant difference in the composition of the milk due to these factors.
  7. Soluble calcium available in the milk
    If milk contains a shortage of soluble calcium this will lead to a soft weak curd. All milk has natural soluble calcium, but you don’t know how much. You cannot see it, taste it and you don’t have the facilities to test its strength. The additional of calcium in the form of Calcium Chloride to the milk will definitley help strengthen your sets. Ensure that if you are adding Calcium Chloride, you do so at least one hour before the addition of the rennet or the positive effect of the additional calcium will be heavily reduced.
  8. Heating of milk:
    Excessive heating of milk precipitates the soluble calcium so it is not available when you add the rennet. Heating is mostly carried during the pasteurisation. It is important not to overheat raw milk in the pasteurisation step. Stick to the recommended pasteurisation time and temperature combinations. Many commercially available milks are pasteurised in large continuous pasteurisers (known as High Temperature Short Time) and the ‘high temperature’ component is great to increase the shelf life of these milks, unfortunately this higher temperature precipitates some of the soluble calcium. If this is the case the addition of Calcium Chloride is very important.
  9. Age of milk:
    Milk that is several days old will not set as well as fresh milk. Some of the natural occurring soluble calcium in the milk will have precipitated. Plus, the proteins may also be affected by the action of unwanted bacteria in the milk as it ages.
  10. Quality of the rennet
    Rennet needs to be fresh and stored in the fridge. It should not be frozen. Rennet tablets are for quantities around 30 – 50 litres of milk are not accurate when using in smaller volumes plus powdered rennet is not as effective as using liquid rennet.

Factors to consider when handling your rennet:

  • Never use rennet syringes that have been sanitised in a chemical
  • Always sanitise syringes and graduated cylinders in hot water
  • Always store rennet in the fridge, never freeze
  • Dispose of rennet when its best before date is reached and get a new batch
  • Know the strength of the rennet you have and the exact dosage and strength of the rennet to be added to the milk eg 10ml of 100 IMCU strength rennet is the same as 5 ml of 200 IMCU strength rennet (IMCU = International Milk Clotting Units and is the standard measure of rennet strength)

Foot Note: Many people use the practice of diluting their rennet in 20 times the volume in distilled or boiled cooled water. This is not necessary for rennet’s that are up to 200IMCU strength. What is important is that the rennet is added over the length of the cheese vat and stirred in very well and the milk is then left undisturbed to set.

Adding Colour to Cheese:

Cheese comes in lots of different colours. The addition of colour to cheeses was historically quite common but in the last 30 years its use in cheesemaking has dramatically decreased.

Colour was added to cheese for cosmetic reasons, to give an appealing brilliant yellow colour.  There is no actual functional use in adding colouring.  The natural yellow colour in cow’s milk cheese comes from the carotene in the cream.  When the cheese is made the loss of the whey concentrates the carotene and leaves a colour darker than the original milk.

Cows are the only mammal with yellow milk.  Cheeses made from sheep, goat and buffalo milk are white.  These animals have an ability to synthesise the carotene in grass whereas a cow cannot.  Cows fed on dry feed during cold winters and housed in barns will also have whitish milk compared with cows that are free ranging, who will have more yellow colouring in their milk.  Breeds such as Jersey and Guernsey will have a more yellow milk than say a Friesian cow.

Annatto

Annatto is the most common colour used by cheesemakers.  It is derived from the berry of the annatto tree (Bixa orellana) which grows in the rainforests of Central and South America.  The English Red Leicester cheese which is red in colour has approximately 20 – 30 times more annatto than a Cheddar cheese.

If annatto is to be used, it is added to the milk when the bacteria or starter culture is added but before the rennet. It is difficult to determine if a colour has been added just by looking at a cheese.  Most cheesemakers choose not to add annatto at any time, preferring to display the natural colours of the cheese. Some cheesemakers will add it all year round for uniformity and some add it only when the cheese milk becomes light in colour (eg when the dry winter feed produces pale coloured milk).

Port Wine

If making port wine cheese, there are a number of ways to get the port wine colour (and flavour) into the cheese.  The most common way is to spike some holes into the matured cheese, and soak the cheese in Port wine for several days.  However an unattractive brown earthy colour sometimes appears and not the rich red port colour.  This can be remedied by adding a small amount of beet dye to the port before the soaking begins.

Other ways to change colours of a cheese

In Sage Derby a green vegetable dye and dried sage herb is added to the cheese just before the curd is hooped.  The colour only adheres to the surface of the curd particles to give a mottled green effect.

Naturally smoked cheeses will have a bright yellow to brown colour as a result of the heat, smoke and some drying of the cheese. Inconsistencies in naturally smoked cheese are very normal.

The red, orange or brown and sometimes neutral colour from washed rind cheeses comes from the brevibacterium linens bacteria that is washed onto the surface of the cheese which breaks down the proteins into desired flavours.

Herbs, grape skins (marc) husk and alcohols such as wine, beer and spirits can be used to wash the outside of cheese.  Sometimes cheeses are soaked in these solutions for several days.  The solution is usually diluted with distilled water and a small percentage of salt added.

Pasteurisation of milk for home Cheesemaking

With the release of the first raw milk bleu vein cheese made in Australia (Udder Delights King Saul), it is probably timely to cover the issue of pasteurisation of milk for home cheesemakers.  This article is not about the pros and cons of using either raw or pasteurised milk it is about how to pasteurise raw milk in a home situation.
The government in Australia requires that milk is pasteurised and milk products such as cheese be made from pastuerised milk. There are a few exceptions for some imported cheeses and a few Australian made cheeses such as King Saul and for raw goat milk in a few states across Australia.

However the law does not require milk produced from your own cows and goats, intended for home consumption, to be pasteurised.

The reason for pasteurisation is that raw milk is a rich product that supports the growth of a large number of microorganisms. The milk as it comes from the cow’s udder is almost sterile and it picks up numerous microbes on its journey through the cold chain. The environment where the milk is produced on the farm has numerous microbes: some may be pathogenic or disease producing, some may be spoilage and some may be beneficial bacteria required to make raw milk cheese.

Some of these microbes will find their way into the milk. Unless you have access to a laboratory you will not know which type and how many microbes are actually in the milk.

The temperatures used to make cheese requires the same milk to be held for up to a few hours at temperatures between 20°C and 40°C  where any microbes (the good, bad or pathogenic) can grow and multiply. If a significant number of disease producing bacteria grow they can potentially cause serious illness to those persons consuming the cheese.

Time and temperature treatments for milk pasteurisation

Pasteurisation requires the milk to be heated to a time and temperature combination that will destroy the pathogenic microbes in the milk. Unfortunately the good or starter bacteria will also be destroyed. Starter cultures are added back into the pasteurised milk as a replacement for the ones destroyed by pasteurisation.

There are numerous pasteurisation time and temperature combinations available but the four most logical treatments for use by home cheesemakers, based on the equipment most people will have available are:

69°C for 1 minute
68°C for 2 minutes
66°C for 5 minutes
65°C for 10 minutes

By properly pasteurising milk you will:

Destroy all pathogenic bacteria and make the milk or cheese safe for human consumption
To destroy some of the spoilage bacteria and enzymes and therefore improve quality of the cheese
Increase the shelf life of the milk

How to batch pasteurise at home:

In the batch pasteurisation process the milk is placed into a pot and heated, usually on a stove top to one of the required temperatures. Some people will do this by placing the pot directly on the heat source (eg stove top) and others will place the milk in a double boiler.

The latter has a less severe effect on the milk and is the preferred approach. The milk will need to be stirred continuously but very gently while it is being heated. When the required temperature is reached heating should be stopped.

A warning note: The above time temperatures are the minimum required to pasteurise the milk for making cheese however additional time and temperatures are also not desirable as they may cause some damage to the milk constituents and make cheesemaking more difficult.

When the maximum temperature is reached, the milk will need to be held for the required time, and cooling commenced immediately. Do not continue with a higher or longer heat treatment thinking it is better. Be aware that the pot and the stove top will also contain residual heat and this may alsocause the milk temperature to continually rise past the minimum temperature.

When the holding time is reached continue cooling the milk straight away, do not delay the cooling so be prepared. You will need to have a supply of cold tap water or refrigerated water to start the cooling process. A sink, a bucket or an outer boiler can be used to hold the cold water. Ice or refrigerated water can be used, it is beneficial but it is not necessary.

You will find that the cooling water in the outer jacket will increase in temperature and will need to be discarded for a new batch of cooling water. Most damage to the milk is done while it is above the 55°C temperature, so it is desirable to cool the milk down below this temperature as quickly as possible.

Continue cooling the milk until it reaches the desired cheesemaking temperature. You are now ready to start making cheese. The same time and temperature standards apply to milk from cow, goat, sheep and buffalo.

Pasteurisation will cause calcium precipitation so it is helpful to add calcium chloride to the milk as soon as it is cooled to cheesemaking temperature. Pasteurisation may extend the time taken to coagulate the milk, give a softer curd and make drainage of moisture from the curd more difficult.

Can you use homogenised milk to make Cheese?

If you want to make cheese, you have a choice of using either homogenised or non-homogenised milk. Fifty years ago the only options were raw or pasteurised milk; homogenised milk was not readily available. Now the situation has reversed, it is a little harder to find non-homogenised milk, but most states in Australia have several dairy farmers that are turning the milk from their own cows into pasteurised but not homogenised milk.

When you purchase milk from a supermarket, quite often the only choice is pasteurised homogenised milk. Homogenisation and pasteurisation are two very separate processes. The law requires all milk sold in Australia to be pasteurised milk; it is illegal to sell non-pasteurised or raw milk. Homogenisation is optional as long as it is declared on the label of the bottle or carton.

If you want to make cheese, you have a choice of using either homogenised or non-homogenised milk. Fifty years ago the only options were raw or pasteurised milk; homogenised milk was not readily available. Now that the situation has reversed, it is a little harder to find non-homogenised milk, but most states in Australia now have several dairy farmers that are turning the milk from their cows into pasteurised but not homogenised milk. I use only non-homogenised milk at the Intensive Cheesemaking and Intensive Yoghurt Making courses.

So, which milk should you choose to make cheese?

The answer is non-homogenised milk. Why? Let’s start with an explanation of why milk is homogenised. Homogenisation came about because the public wanted the cream evenly distributed through the milk as opposed to having the cream layer at the top, where the bottle or carton had to be shaken before being poured. A secondary effect of homogenisation is that it generally lasts a few days longer than non-homogenised milk. Initially homogenised milk was met with scepticism but now it is readily accepted.

Milk is homogenised by passing it through very narrow openings under very extreme pressure. These openings are called homogeniser valves. These valves shatter the fat and proteins in the milk into billions of much tinier pieces. The cream can no longer rise to the surface and is evenly spread through the milk. That the fat globules have been broken up does not affect the cheese. The flow on effect for cheesemaking is that the very high pressure of homogenisation also breaks up the proteins into much smaller pieces. These proteins are needed in their “whole form” to turn the milk into a curd when the rennet is added or the curd does not form properly. Homogenised milk will still form a curd but it is a very weak and the resulting cheese is much lower quality. It is for this reason that commercial cheese manufacturers the world over do not use homogenised milk to make cheese.

There are a few minor exceptions where you can use homogenised milk to make cheese. Both homogenised and non-homogenised milk can be used to make Ricotta. Homogenised milk can also be used to make gourmet feta because it requires a soft curd.

So if you want to make good cheese, use non-homogenised milk. If you want milk with a full flavour and lots of body use non-homogenised milk. Don’t let anyone tell you otherwise.

Using a brine to add salt

Salting involves the spreading and distribution of salt through a cheese. There are two ways to add salt to cheese: by immersing the cheese into salt water, which is called brining or by physically or mechanically adding the salt to the surface of the cheese which is called dry salting.
There are several key reasons that salt is added to cheese and all are very important for the quality of the finished cheese:
Alters the texture and appearance
Slows down or stops lactic acid fermentation
Controls enzyme activity and subsequent breakdown of fats and proteins
Suppresses the growth of spoilage bacteria
Aids moisture control
Improves flavour

Brining is the immersion of the whole cheese in a sodium chloride solution. Most brines are around 20% – 27% salt content. Once 27% salt is reached that is called the saturation level for salt in water. Brining is thought to have come about because if dry salt was not available then partially evaporated sea water would serve the same purpose.

When brines are used, the following principles should be followed:
Brine storage vessels should be made from non-corrosive material
The volume of brine should be at least 1.5 times the volume of cheese
The amount of salt to be added is calculated from the desired brine strength, for example 20% brine for white mould cheeses
If reusing a brine, the salt strength should be monitored and salt needs to be added to ensure concentration is maintained
The pH and calcium content of the brine must be maintained so that these two components roughly equal the same level as the cheese
Ideally brines should be refrigerated between uses but also ensure they are handled correctly as they are very corrosive
The mechanism of salt uptake of salt from the brine to the cheese is similar to that of dry salting.
The salt that is taken into the cheese from the brine and whey (including moisture and some minerals) is then expelled from the cheese into the brine. This transfer is not always even, as a general rule two grams of water is lost from the cheese into the brine to every 1 gram of salt taken up by the cheese.
A variation in salt uptake means that different styles and sizes of cheeses will require different amounts of time in a brine.

Variation of the rate that salt is taken into the cheese can be achieved by:
Different concentrations of brine (20% salt v’s 27% salt)
Length of time the cheese in the brine solution
Moisture content of cheese
Temperature of brine
Surface texture of cheese
Surface area, size and shape of cheese;
Agitation of brine solution
Hardness of the cheese
Fat and protein content of the cheese

Making and using a salt brine
The water used to make up the initial brine should be straight from the tap and heated to at least 80c to kill any unwanted bacteria and the salt should be added to the hot water. The salt for making up a brine does not have to be premium fine cheesemaking salt, as this type of salt can be expensive. The cheapest non iodised supermarket salt is suitable. The salt should also ideally be free from foreign matter, however if the salt does have foreign matter it will be rendered safe by the hot water and the salt.
When a salt brine is first made up it is necessary to add approximately 1ml of acetic acid and 1ml of calcium chloride for every litre of water so that the acid and calcium levels of both the brine and the cheese are equal. The purpose of adding CaCl to the brine is to maintain the same concentration of calcium in the brine and in the cheese – if the calcium concentration is too low in the brine then calcium will move from the cheese to the brine to establish equilibrium concentration in the brine vs the cheese. If the calcium leaves the cheese then the cheese will go soft.

When the cheese is sitting in the brine, it is ideal to sprinkle a pinch of salt over the surface of the cheese that is protruding from the brine. The cheese should be turned 180 degrees a few times during the brining process.

It is ideal to reuse a brine as it builds up with substances such as lactic acid, proteins, minerals, lactose and moisture from the cheese however many people will not have sufficient space to store their brines in a refrigerator between use. If reusing a brine any floating pieces of curd should be removed before use.

Why is the size that you cut the curd important?

The size that you cut the curd will affect the moisture and characteristics of your cheese.
The cutting of the curd that has been formed after the addition of the rennet is one of the most critical aspects of cheesemaking.  Cutting is the start of the dehydration process and will affect the final moisture, acidity, maturation rate and yield of the cheese. All of which are very important factors that distinguish the exact characteristics and quality of a cheese. After the curd is cut it holds the main constituents of the cheese which are the fat and casein plus it also contains some water, minerals, whey, starter culture and rennet. The constituents that are lost in the whey are the water, lactose, whey proteins, some minerals and a small amount starter culture. The term used to describe the loss of these components is called syneresis.

The volume and the amount of these constituents that are either retained in or removed from the curd are very closely related to the surface area of the curd particle after it is cut. The general rule is that the smaller the size of the cut, the greater is the surface area of the curd and the greater is the loss of components into the whey.

To show this: If we started with 1 litre of milk and added rennet so that it formed a cube of curd. We would have a 10cm cube of curd; the surface area would be 600cm cm² (6 sides to a cube). If that cube of curd was cut into 1cm cubes (Cheddar cheese is cut to this size), then we would have 100 cubes with a surface area of 6000cm².  If we cut those 1cm cubes into 5mm cubes then we would have 8000 cubes of curd with a surface area of 12,000cm².  Simply put the more surface area means more loss of whey and constituents into the whey.

Different cut sizes for a few cheeses may be:

·      Parmesan styles 2 – 3mm

·      Cheddar 8 – 10mm

·      Camembert 12 – 15mm

·      Persian feta very large pieces

How to check if your thermometer is accurate

I receive regular emails from people that have been using their thermometers for fairly long periods of time but they are not sure if they are working correctly. Checking your thermometer is something that you should consider doing every several batches of cheese.  It is very simple and quick to do and can give you good peace of mind.

How do thermometers become incorrect?

Regardless of how much you spend on a thermometer, $10 or $1000, they are all capable of providing an inaccurate reading.  Inaccurate readings can be caused because it was dropped, you changed a battery or it’s just one of those electrical/mechanical things that happens from time to time. If you are using a non-water resistant or non-water proof thermometer to make cheese then the electrics of the thermometer may be starting to deteriorate due to water damage of the internal components.

What is a satisfactory level of accuracy for a thermometer?

For most people making cheese at home, you should be happy with your thermometer if it is within +/– 1°C or even 2°C of a true and correct reading.  However if your thermometer is out by any more than this it may affect the quality and consistency of the cheese you are making.

How do I check the level of accuracy?

There are two standard methods that you can use at home to check your thermometer.  The Ice Bath or Freezing Point method and the Hot Water or Boiling Point method.  You can check your thermometer by using either or both of these methods.  If you are making yoghurt or ricotta where you are heating the milk to i.e. 90°C then the hot water method is best for you to use.  If you are using cheesemaking temperatures around 30°C then the ice bath method is best to use.  If you are using both high and low cheesemaking temperatures then use both methods.  It does not take long and it’s a good idea to check your thermometer against both methods.

The principle of these two methods is that a pure ice and water mixture will hold its temperature temporarily at 0°C and that pure water will boil at 100°C. If your thermometer is placed in either of these mixtures then ideally it should read the same temperature as the water bath.  A description of the 2 methods follows:

Ice Bath method

Materials needed: 1 litre clean and dry container (glass or plastic), 300 grams of crushed ice (not ice cubes), 200 ml of the purest water available (filtered water is best but tap water is ok providing it is not overly hard with minerals), thermometer/s to be checked

Immerse the thermometer probe by more than half way in the ice and water slurry.  The mixture should be a slurry and not have large chunks of ice.  Hold the thermometer in the ice water bath and move it around in a stirring action without touching the sides of the water bath.  Do this until the thermometer reading stops moving.  The reading on your thermometer will show how accurate your thermometer is (it should read 0°C).

Boiling water method

Materials needed: Approximately 1 litre of the purest water available (filtered water is best but tap water is ok providing it is not overly hard with minerals), a 1.5 to 2 litre saucepan, thermometer/s to be checked.

Add the water to the saucepan and place on the stove top until water boils (when there are bubbles rapidly rising to the surface, not just simmering). When boiling commences turn the stove top down to its lowest setting but be careful to make sure that the water is still boiling. Immerse the thermometer probe by more than half way into the boiling water. Move the thermometer around in a stirring action without touching the sides of the saucepan. Do this until the thermometer reading stops moving.  The reading will show how accurate your thermometer is (it should read 100°C).

How to adjust the thermometer if the reading is inaccurate?

Not all thermometers can be adjusted. Both of the thermometers that I provide on the Cheesemaking Shop  are waterproof and have an ability to be calibrated by the freezing point or boiling water method. Manufacturer’s instructions are provided with each thermometer. When you test your thermometer and it is out by i.e. 2°C then you can adjust the thermometer by holding down the calibration button on the thermometer. If your thermometer is not adjustable then then next time you make cheese just add or subtract that difference each time you take a thermometer reading when you make the cheese.  If the thermometer is out by more than 2°C you can still do the addition or subtraction, but it is probably time to look at replacing your thermometer

Pressing and moulding cheese

The purpose of pressing and moulding of cheese is to:

Produce the desired size and shape of cheese
Form all of the individual particles of curd into one cheese that can then be ripened, packaged and stored
Speed up removal of free whey
Consolidate the curd by removing the air and spaces between curd pieces
Create the initial stages of rind formation

The main variables that need to be controlled during pressing are the amount of pressure applied to the cheese, how fast pressure is applied, the temperature of the cheese during pressing and the length of time the cheese is pressed.

The amount of pressure

Some cheese such as fresh acid, blue mould and white mould; the curd is moulded and no pressure is applied, the cheeses are simply turned 180 degrees and allowed to be pressed under their own weight. Cheese such as Cheddar and Emmenthal are pressed at high pressures for several hours. In the case of eye-type cheese, prepressing may take place under the whey, usually after the curd is placed in the mould.  Other cheese such as Tilsit and Havarti with some eyes and openness only have a moderate amount of pressure applied.

Applying pressure slowly

Pressure must be applied gradually to ensure that whey and air can escape through the natural channels between the curd pieces before pressure builds up sufficiently to close off the channels.  30 – 60 minutes is sufficient time before the full pressure is applied.

The temperature of the curd

The curd needs to warm when it is placed in a hoop just prior to pressing.  Curd particles that are cold or have dried out will be hard and will not matt together sufficiently.  If curd is salted prior to hooping (eg Cheddar) then the curd needs to be kept warm to allow the salt to slowly diffuse into the curd for approximately 10 minutes prior to being moulded and pressed.  The curd should be kept warm while it is in the press.

The length of time the cheese is pressed

Pressing time can vary from 30 minutes to 24 hours. Pressing needs to be applied slowly at first and then gradually increased.  This allows air and moisture to move from via natural channels from the inner to the outer layers of the cheese.  Pressing at a too fast rate may close these channels and trap air and moisture in the centre of the cheese.  The cheese hoop or mould should be lined with a cheese cloth, which can be made of cotton or synthetic material (blue cheese cloth) to aid in drainage of whey and to produce a smooth close surface finish. Once the cheese has been pressed, it is usually taken from the press after about 30 – 60 minutes, to straighten the outer cloth so an even surface results on the finished cheese. The cheese is then usually pressed overnight.  The following morning the curds have cooled considerably and ‘set’ so additional pressure should not be applied the following morning.  Keeping the curd warm after pressing is important especially on cool days.  .

There are a large variety of cheese presses used by home and commercial cheesemakers.  Pressure can be applied by hydraulics, spring or by vacuum.

What are those hard white crystals in mature cheese?

Have you seen those small white crunchy specks on and in hard cheeses such as Cheddar and Parmesan? They are called calcium lactate crystals. They are part of the cheese and they are harmless. They are usually pin head size and some cheeses have a few and some cheeses have lots.

These crystals are often sought out by connoisseurs of such cheeses as being indicative of a mature cheese with a strong flavour, but they are also misunderstood by others as being foreign matter or extraneous to the cheese. Calcium lactate is formed as the lactose in serum (residual moisture in the cheese) is turned into lactic acid as the cheese ages, the casein bound calcium is released into the serum and this combines with the lactic acid to form crystals over several months. There are several factors that may cause these crystals, the main ones are too much acid and too much moisture in the cheese. Other factors include slow cooling and high maturation temperatures.

The big question: If you could purposely make a cheese with Calcium Lactate Crystals would you?

Why is Ash added to cheese?

There are many famous cheeses around the world that have ash added to them. Sainte Maure, Morbier, Valencay, Selles ser Chur, plus local cheese such as Meredith Ashed Chevre and Yarra Valley ashed pyramid are just a few. But why is ash added to these cheeses? It is tasteless and odorless!

For thousands of years ash was used as a preservative, to stop lumber from rotting, bodies from decomposing, preserving food and water on long sea voyages, filtering muddy water, controlling odours and as a powerful medicine. Cheese also needed to be preserved especially as there was no refrigeration or the advantages of modern packaging. Originally ash was obtained from burning oak branches, grape vines or local timbers. The ash was sprinkled on the surface of the cheese often in conjunction with salt.

There are five main reasons why ash was added to the surface of the cheese:

1. To decrease the acidity of the cheese. Where the cheese has a high acidity, such as fresh acid cheeses (cheese made without the use of or minimal use of rennet; most of the cheeses mentioned above are this style) the ash will neutralize the surface acidity. The surface flora required of those cheeses, some added to the milk and some occurs naturally, do not grow well in very acid environments but will grow earlier than would be expected if ash is added and results in a more complex micro flora of the final cheese. The ash in this situation also restricts the growth of unwanted micro flora

2. To absorb surface moisture. The surface moisture reduces the hardness of the rind. The rind is the hardened surface of the cheese and is important to protect the cheese inside from drying and physical damage. So if moisture is soaked up soon after manufacture then the hardened rind will be able to preserve and protect the interior of the cheese

3. The addition of salt in conjunction with the ash also aids in assisting points 1 & 2 above

4. Purely cosmetic. With modern packaging and refrigeration and controlled environments the need for ash to preserve the cheese is reduced or not even required.

5. Tradition. Tradition does not need to be lost just because of modern technology. This ash has been used for centuries and is as much as a characteristic of the cheese as the cheese itself. We need to these traditions to be preserved plus the ash is an instantly identifiable characteristic of those cheeses.

Ash is technically known as Activated Charcoal. The word “carbon” comes from the Latin word for coal. Graphite, the most thermodynamically stable form of carbon (as in pencil “lead”) is in the ash family as is the diamond.

Charcoal from burning wood in the back yard is not “activated charcoal”; rather it is a raw material for the manufacture of activated charcoal. Commercially cheesemaking ash it is derived from wood, sawdust / wood chip, coconut shells, bamboo and peat. For food grade purposes these timbers are heated to between 600 °C – 1,200 °C which is much higher than a conventional fire or oven can achieve.

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