Acidity control continued

In depth discussion into the scientific aspects of cheese making.

Acidity control continued

Postby Rik vonTrense » Sun Apr 23, 2006 7:26 pm

Here we go then:

Milk: Lactic acid producing bacteria: Rennet (or other coagulant): and Salt. That's all we need...... Plus total dedication.

Oh, and one other thing...... you must be inquisitive.

Bacteria, from birth so to speak, take time to acclimatize themselves. If they then find themselves in a friendly environment they will reproduce and the numbers will increase rapidly. The numbers will reach a peak and then begin to decline. In cheesemaking this decline is the result of the bacteria themselves having used up all the available nutrients (there may be other reasons, which will be discussed). You, as the cheesemaker, will control the amount of nutrients available to your starter bacteria, and the suitability of the surroundings, and thus extend or limit their acid producing potential.

Lactose is a disaccharide (two sugars) of glucose and galactose. It is dissolved throughout the milk fluid at a volume of around 5%. About 10% of the lactose is consumed during cheesemaking and the rest is lost into the whey.
The lactose is the source of energy, in the form of carbohydrate, that is utilized by the lactic acid producing bacteria (starters). They consume lactose and exude lactic acid as a waste material.
By the end of production most well made cheese will contain close to zero lactose.
The starter bacteria will starve as a result and acid production will cease.

This activity also deprives many other bacteria of a source of energy, and this is one of natures "pathogen controls".

The acidity of the surroundings is all important in the world of bacteria and the absolute optimum acidity at which any given species of bacteria will operate at it's best is within a very small range: one step either way will be the optimum for another organism which will use the same energy source, and may possibly produce substances which are harmful to the competition.

E.coli are bacteria which will utilize lactose as their energy source but, they will only reproduce at an acidity which is low in comparison to that favoured by your starter bacteria. You will find that most pathogens favour lower acid (higher Ph) conditions.
A good starter will generate acid at an even rate (not necessarily fast), thus never allowing the E.coli to feel comfortable enough to start reproducing before the acid levels become too high for it to function at-all or, all the lactose has been used up by your starter and E.coli starves.
Nature's pathogen control at work........ Cheese, well made from good milk, will never present a risk to human health

The principal of acid "control" is the basic principal applied throughout your cheesemaking. You control good cheese by controlling the optimums.

The rate and extent of acid production exert control over every aspect of your cheesemaking.
This includes the viability of the lipase working in flavour production and in body structure.
A lipase is an enzyme, which causes the break down of lipids into fatty acids and the fatty acids are major precursors of flavour.
Lipids are fats. Lysis is the breakdown of a component. Lipid breakdown is known as lipolysis.

Although you can't see or measure the enzymes, you will find that the flavour profile of your cheese will change in relation to the rate and extent of your acid production, which controls the enzyme activity. When you change your acidity, or rates, (and throughout through your cheesemaking you do just this) you change the optimums for the bacteria and their enzymes. Which means of course that you are responsible for the flavour.

It follows, naturally, that the flavour profile of cheese made from pasteurized milk can never be as complex as that of raw-milk cheese.
The enzymes are produced inside of bacteria. Raw milk may contain many hundreds of species of beneficial bacteria, and the only bacteria in pasteurized milk are those which are introduced as starters, or from post-pasteurization contamination. Though the use of enzyme "soups", which are added during cheesemaking in an attempt to re-create flavours and to accelerate ripening, is now widespread in commercial cheesemaking plants. "Accelase" is an example.
The "ase" ending tells us that it is an enzyme and "accel" is self-explanatory.

I notice that many novice cheesemakers in the USA are using what they call "flavour enhancers" along with their starters. These are the enzyme additives I refer to and are totally foreign to real cheese-making.

With freshly drawn cows milk you will expect to register a titratable acidity (T.a.) of 0.15 to 0.17. (This is a P.H of about 6.7). Incidentally, you cannot compare "acidity" to "Ph". You may know some points that match here and there simply from experience though.
As milk passes naturally to the calf it will become contaminated with viable lactic acid producing bacteria (streptococcus thermophilous etc.) which thrive on the milk residue in the mouth of the calf and in the teat canal of the cow/goat/ewe etc.
During the milk's passage through the stomachs of the calf these bacteria will begin to multiply - thanks to the availability of the milk lactose as an energy source and the close to optimum temperature for growth.
Once in the abomasum (fourth stomach) the milk, now acidified, is ripe for the coagulating actions of the stomach enzymes, rennet.

So, we have a natural phenomena: separation of solids from liquid: separated at a relatively low acidity by the effects of rennet and giving the calf a smooth, soft curd to digest (Cf. when a milk-fed baby burps up semi-solids).
Without this "setting" the milk would pass through the animal's intestine too quickly and be only partly digested.
Had the acidity been higher (faster) this milk would still have coagulated but the resulting curd would have had a more grainy and less cohesive body, relative to the acidity, and not have been in optimum condition for absorption.

Milk will coagulate simply from the affects of lactic acid, without the benefit of rennet, at P.h. 4.6. This is what is known as the iso-electric point of casein.
At 20c this will take around 24 to 36 hours depending on the starter.
Fresh cheese made purely through this lactic coagulation will have high acidity and a very fragile body comprised of fine flakes or grains with little cohesion. The particles will be very porous and hold lots of moisture.
These " lactic " spoonable cheeses are usually sold either absolutely fresh or, packed in airtight containers and chilled.

The elasticity (cohesion) of the curd is dependent on the mineral calcium and this is "fractured" by acid and will then drain from the curd along with the whey.
The greater the acidity at coagulation time the less calcium will have been retained and the less cohesive will the resultant curd be. It will also retain more moisture since it becomes more porous with the loss of calcium.
You might think of calcium as the natural "glue". How much "glue" you allow your curd to retain will depend on how firm or soft, or dry or wet, you want the mature cheese to be.
Commercial producers will add extra calcium to the cheese milk as it means that they can work at faster and higher rates of acidity than is traditional. They will give you other reasons but the truth is that fast acid rates upset the calcium balance and this needs to be restored artificially.

The Artisan cheese-maker should beware of using commercial cheesemaking practices as criteria for their recipes. You do so only at the cost of complexity of flavour and personality.
This will lead to a devaluation of your products as commercial plants continue to "improve" the flavour profiles of cheese made from pasteurized milk.

Lactic Cheese: is coagulated slowly, 24 to 36 hours, at high acidity and low temperature; it lacks calcium, has a high moisture content, a loose and inelastic body, and a very short shelf life. It will desiccate very quickly if left exposed.

Renneted Cheese: coagulates quickly (20 minutes to 2 hours usually) at lower acidity and higher temperatures, it retains more calcium, has a lower moisture content, an elastic body, is often pressed and has greater keeping qualities.

Where Lactic coagulation & Rennet coagulation meet is your cheese. You are constantly working with a balance within these two extremes.

If you make soft or pliable cheese types you will be attaining a fairly high acidity (low elasticity) but relatively slowly.
If acid production is too high, or fast, you will make hard dry cheese lacking in flavour.
If it is too low, or slow, you will make a sticky mess prone to gas formation, or, a hard wet cheese.

If you make a hard-pressed cheese you will be working towards a lower acidity
(high elasticity) but faster.
If it is too fast you will make a hard dry cheese lacking in flavour.
If it is too slow you will make a soft bodied, poor flavoured cheese prone to gas formation.

Rennet: is a concentration of live chymosin and pepsin enzymes extracted from the dried vells (stomach membranes) of un-weaned ruminants. It will cause milk to coagulate quickly at, and below, P.H 6.5 (Ta. ~ 0.18). How, is another story.

Similar coagulation can be achieved by stimulating certain moulds or yeasts to produce large numbers of other enzymes which will coagulate milk, often known as "vegetarian rennet" (Modilase, Renilase etc.).
There is now also the laboratory produced "Chymogen" which is a genetically engineered synthetic chymosin enzyme (the base DNA used in these genetically engineered coagulants is usually derived from E.coli or from the mold Aspergillus niger, both of which can produce toxins). "Chymogen" is a trade name but other companies produce and market these genetically modified coagulants under similar names.
The use of these is illegal in some countries, though (at the time of writing) they are used in around 80% of British cheesemaking. Personally, I find the use of genetically modified organisms in food to be quite frightening.

The coagulant you use will help determine the flavour, aroma and body structure of your cheese.

Cynara cardunculus:

The plant "Cardoon" naturally produces an enzyme (Cardosine A) which will coagulate milk.

This is a true vegetable coagulant and is used by most Artisan cheesemakers in Portugal.
It is a member of the artichoke/thistle family. The flowers are plucked and dried then infused in warm water into a tea which is then used in the same way as one would use rennet: I usually use around 25 grams of dried flowers, twisted into a bag of cheesecloth, to a large cup-full of warm water to make up mine.
I am not sure that it would be suitable for a cheddar-type cheese as it produces a more delicate set and, in my experience, seems to be rather more proteolitic than rennet. It has a quiet different life about it and it needs a perceptive person to work with it. { The amount you use will vary for many reasons... try 5 ml. of the mixture per litre of milk as a jumping in spot}.
It grows fine in the U.K. and is perennial.

The coagulum of milk set mainly by the action of rennet (or other enzyme coagulants) will be so homogenous as to be jelly-like, since it will have set quite quickly at relatively high temperature:
it will not be very acidic and will not have lost much calcium "glue".
It will have shrunk slightly, and enclosed a lot of moisture within itself. That is, within it's mass, not within the actual particles.
All of the lactose will be accessible to the starter and the main acid production will start during coagulation.
It is at this time that the acid producing starter bacteria are most active: it is warm and there is a high concentration of lactose available in the moisture to supply the energy to reproduce.

If we simply leave this coagulum undisturbed for some hours it will become very acidic.

If we cut or break the coagulum so as to cause it to loose moisture, and lactose, then the resulting curd will be less acidic in the same number of hours.

If we actually remove some of the moisture (whey) then the resulting curd will be even less acidic.

The amount of acid produced within the curd from now on, you control through temperature and the rate at which it is applied, the time that you allow the moisture to remain in the curd, your cutting, stirring, pitching, texturing, room temperature, milling, pressing, molding, type of mold, humidity, turning, salting. These are all acidity control points and will all influence body and flavour.
If you make cheese already you are using these controls.

If you take 20 litres of milk, take it to 20/21 centigrade, add 1% starter (this is about equivalent to what would be used in the average British hard cheese) and leave it undisturbed in an ambient temperature of 20/21c, it will coagulate in 20 to 24 hours.

It will form a very delicate curd. If you handle it gently you can scoop the curd into a coarse muslin cloth which you should tie and hang to drain for a further 24 hours at 20/21c, then hang in a fridge at 4c for 24 hrs to produce a wonderful Quark cheese. It is usually lightly whipped before serving or potting.

This is Lactic cheese. In other words, the coagulation results purely from the effect of lactic acid and is rennet-free.

If you add just one drop of rennet to the milk you are taking the first step towards rennet cheese: the curd will set sooner and will be more cohesive, and will be closer to the modern Fromage Frais. One more drop and the curd will be stiffer and more suitable for cheesecakes etc. There's a limit of course.

The acidity must still be allowed to rise for the full term before the curd is disturbed. The more acid the curd the deeper will be the surface layer of free whey, and the more likely you are to observe cracks in the curd surface.

You will probably find that when the ideal acidity is attained you will see that the curd is just beginning to shrink away from the sides of the vessel, and there are perhaps just one or two small cracks in the curd surface.
The acidity at which you disturb this curd is extremely important to the quality.

You should take a reading of the whey acidity before you disturb the curd, then when you make a first rate cheese curd (not too acidic and fragile, and not under acid and stodgy) you will have a guide for every make. In fact, you will have a recipe and in future you will ladle/cut according to acidity and use time merely as a guidline.

You may increase or decrease the acidity simply by extending or decreasing the time, or by increasing or decreasing the amount of starter. Temperature changes will affect acidity rates but will also affect the curd shrinkage and body.

The most common causes of failure are poor temperature control and poor starter management.

The whey in which your cut curd is floating contains lactose; if you reduce the lactose available to the bacteria within the curd then you reduce their life span and acid producing ability.
The point at which you remove the whey is a major acidity control. The sooner you remove it the slower will be the rate of acid production during the rest of the make.
The smaller you cut or break the curd the slower will be the rate of acid production. This applies whatever cheese type you are making. If we were to cut our curd into 1-inch cubes each cube would have 6 square inches of surface area from which to loose moisture. If we cut these cubes in half we will now have 8 square inches of surface area, and so on.

As the available lactose decreases the bacteria recognise this and will reproduce ever more slowly to avoid over- producing competition for the failing nutrients.


The curd shrinks and looses moisture through the influence of heat, acid, and of rennet: and through physical pressure (stirring etc.).
With any cheese, the way in which you handle the curd throughout cheesemaking will influence the acidity of that days make.
The more roughly, or firmly, you handle your curd the faster it will loose moisture (containing lactose), and therefore will have a lower potential to produce acid. The more you leave it undisturbed and the more gently you handle it the more it will acidify. The French have a wise old saying that it should be handled "like a bride".

Pressure at any stage before salting will influence acidity.
In fact, any physical action which assists drainage will reduce the acidity potential by reducing the amount of moisture in the curd and, along with it, the lactose which is the energy source for the remaining starter organisms.

With experience, you will eventually be able to quite easily "read" the acidity of the day's curd simply by the feel of it related to time.
The more fragile the more acidic. The more stodgy the lower the a basic.
Don't kid yourself too soon though.

As you will see, what you do at any given point usually has no immediately apparent influence on your cheese: it all takes time.
This is where your acidity readings and log become your back door into what is going on in there.
Once you know what the acidity should be at certain stages then, in the midst of a make, you will be able to decide whether or not you need to increase or decrease the rate from then on in order to maintain the right balance for your cheese.

How do you find out what the acidity should be at these "stages" ?-----

Well, first off, you make a cheese, whilst being guided by a recipe from whatever source that is somewhere in your mind around what you would like to make.

You will see cheese grow in your hands. Study what is happening, study your curd, take acidity readings and you will begin to recognise "high" and "low", "fast" and "slow", "wet" and "dry". If you can follow a cheese throughout it's life you will begin to assimilate all, from the milk to the end effect.

Don't worry too much about mistakes, there is no such thing.. it is all learning, and every mistake adds to your experience.

When, one day you make a "great" cheese, you will know how you did it, and you will keep that basic record come hell or high water. When your readings wander from the norm, and what you make is not great or it just doesn't feel right today, ask yourself why? Compare the logs and see what is different. Listen to what your cheese is telling you, feel it, talk to it, and assimilate everything you can from it at every stage. Cheesemaking is not something you can do now and then�. you must live with it ! Then you must learn how the seasonal deviations in milk and weather will call for changes in your making.

If you have come this far then you realize that you have not set yourself an easy task. The rewards though, of working with nature, are overwhelming.


Try not to make more than one change at a time to your recipe.

You have a limitless number of possible combinations to work with but one group will apply uniquely to your cheese, and you will get to know them much sooner simply by listening to what your log has to say. The variations can often produce favourable end results but, if you have no record of what you did it can take years before you are able to repeat it, and it is so easy to get lost by wandering further and further in the wrong direction.

You probably won't see the end results of your actions for some weeks or months even, and it is extremely unlikely that you will remember every one of your actions over this period. You must keep an honest Log !

You should be aiming always for that "golden" cheese, and a good cheese-maker is able to control the make to such an extent that any deviation is minimal.
This is not standardization; this is simply good cheesemaking practice.

All this may seem rather nebulous to some of you but, we'll get there.

You may find some morsels here that will interest you but they are all necessary for the cheesemaker if he is to become good.

Rik vonTrense
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Rik vonTrense
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