Cheese and Yoghurt Making

GENERAL NOTES ABOUT MAKING YOGHURT
Yoghurt is simple to make if you follow some basic rules. 
When incubating the yoghurt, temperature is very important.  The two bacteria in yoghurt have different characteristics, which influence the yoghurt flavour and body.  If the temperature of the milk is too warm during incubation, then one of the bacteria in the starter will proliferate and the other will not. This will result in an imbalance in the starters, producing a weak bodied yoghurt with a strong acid flavour.  The best results are found by incubating the yoghurt at precisely 42 to 43°C.  The incubation time should be about four to six hours. The yoghurt makers that Cheeselinks sell are ideal for keeping the milk at this temperature (or if you are having a heat wave like Melbourne and Adelaide at the moment, you could just leave your yoghurt outside for the day!)

European yoghurts are often incubated at much lower temperatures (32 to 38°C), but the time of incubation will to be closer to 10 to 16 hours.  If yoghurt is incubated at too low temperature, it may tend to go stringy or slimy. 

The yoghurt will coagulate during the incubation, but it is generally not placed in the refrigerator until about one hour after coagulation.  The time allowed after the yoghurt coagulates and before refrigeration will determine its flavour intensity.  To make a stronger flavoured yoghurt, simply leave it longer before cooling.  To make a milder yoghurt, refrigerate soon after coagulation.

STEP BY STEP INSTRUCTIONS FOR YOGHURT MAKING USING YOGHURT MAKER:

• Boil water (on the stove or an electic kettle)
• Place your spoon and plastic container in boiling water for at least two seconds to sanitise
• Pour your milk into the sanitised container. UHT milk is ideal, but if you have fresh milk you need to heat treat it first (see instructions for heat treatment below) 
• Optional Step: Add approximately 100g full cream milk powder or skim milk powder to your milk. This will make the consistency of your yoghurt thicker.
• Add about 1/10th of a teaspoon of yoghurt starter to 1 litre of milk. You can choose from any of the Cheeselinks range depending on the flavour profile you prefer in your yoghurt.
• Mix together with a sanitised spoon
• Put the container in the yoghurt maker and turn on.
• Let the yoghurt set for 6-8 hours, or until it is coagulated and to your taste.
• Once set, place into your fridge and store at 4 degrees C.
• Add sweeteners or flavours as desired.

 

Some ideas for things to try mixing into your yoghurt:

• Honey or brown sugar
• Muesli
• Vanilla essence
• Stewed apricots
• Fresh passionfruit
• Strawberry jam (or any flavoured jam will work)

 

Our most recent newsletter has a great article with ideas to try with your yoghurt, so we encourage all of you to subscribe now by sending us an email!

 

ADDING FLAVOURS TO YOGHURT

Essences or sugar can be added to the yoghurt before adding the culture.  Just be careful if adding sugar as too much sugar can inhibit the growth of the starter bacteria.  If you want a very sweet yoghurt you can add the sugar after the fermentation. 
When adding fruit to yoghurt, either make sure that the fruit has been heat treated (to ensure that if there are any organisms or enzymes in the fruit they have been destroyed) or if you want fresh fruit, add just before eating the yoghurt.  Do not stir fruit or flavours into the yoghurt until the yoghurt is cooled as this may cause the yoghurt to separate into curds and whey. 

 


GREEK STYLE YOGHURT
Greek style yoghurt can be made by one of two methods.  The first is to make the yoghurt as per the yoghurt recipe and then drain the yoghurt through a cheesecloth until the yoghurt is thick enough for your liking.  Usually it is drained to half its original volume.  The second method requires 100 grams of full cream milk powder to be added to each litre of milk and make the yoghurt as normal.  It may take a couple of hours extra to set. 




OTHER ORGANISMS IN YOGHURT
There are other organisms that can be added to yoghurt. These are usually classed as probiotics.  These include, but are not restricted to Lactobacillus acidophilus, Bifidobacterium bifidus and Lactobacillus casei. These organisms can survive the intestinal system and can be found alive in the faeces. In very few cases are these organisms used to actually culture the yoghurt, but are added as an adjunct. 


 

USING EXISITING YOGHURT AS A STARTER FOR YOUR YOGHURT
If you use existing yoghurt as a starter for your yoghurt you will get inconsistent results. The different types of bacteria in the yoghurt die off during storage. The yoghurt may contain all of the bacteria but not necessarily in the correct ratios. If the yoghurt you use contains acidophilus or Bifidobacterium then it is a waste of your time subculturing from that yoghurt and expecting to have these bacteria in the resultant yoghurt.  If you want yoghurt with good levels of acidophilus or bifidus you will have to use starter powder each time you make the yoghurt. 


In regular yoghurt the two bacteria grow optimally at slightly different temperatures, and have different acid tolerance. This means that the yoghurt that you are using as a starter will have the individual bacteria present in different levels. This will mean that the balance of flavour will change as will the flavour and texture of the yoghurt. 

 

HEAT TREATMENT OF YOGHURT MILK
When making yoghurt, the milk should always be given a substantial heat treatment.  Milk for yoghurt making is heat treated above pasteurisation temperature to increase the water binding capacity of the proteins and therefore to increase the viscosity of the resulting yoghurt.  Another of the reasons for high heat treatment is to destroy the spoilage bacteria present in the milk.  With these bacteria gone, the yoghurt starter has no competition and can produce the lactic acid and flavour that is typical of yoghurt. 


Even pasteurised milk is not sterile.  There are a number of thermophilic (heat loving) bacteria that survive the pasteurisation  process in the milk. 
The addition of milk powder to milk for yoghurt making is done to provide a thicker yoghurt and can be added in amounts to suit your preferences.  The heat treatment should always be done after the addition of powder, so that any bacteria in the powder are also destroyed. 
If you are heating in a saucepan, the heating must be done carefully so that it does not burn on the base of the pan.  If this happens then your yoghurt will have a cooked or burnt flavour.


PROCEDURE FOR HEAT TREATMENT

1. To each litre of whole milk, mix in 30 gm of skim milk powder. 
2. Heat to 90°C. A microwave oven is useful to heat small quantities of milk.  If heating in a saucepan on the stove, stir continually to avoid burning milk on the base of the pan.
3. Upon reaching 90°C, remove the milk from the heat source, cover and allow to cool to 42 to 43°C.  You may chose to remove the skin that will form, or stir it back into the milk. Note that Starter addition must not be done until the temperature is under 45°C.  If starter is added with the milk too hot then the starter may be killed.  It is wise to mix the starter in well, so that it is evenly distributed throughout the milk. 

 

TECHNICAL INFORMATION ABOUT YOGHURT


What is YOGHURT?
Yoghurt is a form of preserved milk.  It is preserved by means of acidification. This acidification is produced by the action of the yoghurt bacteria fermenting or converting the lactose in the milk to lactic acid.


The main bacteria in yoghurt are:


-Lactobacillus delbruekii subsp. bulgaricus and (Lactobacillus bulgaricus)
-Streptococcus salivarus subsp. thermophilus (Streptococcus thermophilus).


CHARACTERISTICS OF THE CULTURES: 


The thermophilus produces a mild flavoured, thick yoghurt. The bulgaricus produces an acidic flavoured, weak bodied yoghurt. When both cultures are combined, they grow together symbiotically, and the resulting yoghurt is thicker than either one would be on its own. If one of the bacteria out populates the other, the resultant characteristics of the resultant yoghurt will change. 

 

Basically, the way that these bacteria work is by fermenting the lactose in milk to produce lactic acid.  If conditions are favourable and these organisms have nutrients to grow, they will reproduce, which they do by dividing in half.

 

As the starters reproduce and produce lactic acid the environment of the bacteria becomes more and more acidic, to the extent that it becomes toxic to the bacteria, at which stage they stop reproducing and start to die off. 

 

Therefore the number of live bacteria in the yoghurt will depend on the time that the bacteria have been in the yoghurt and the acidity of the yoghurt. 
You can see from looking at the way in which bacteria grow that if we use yoghurt that is old, there will be very few live bacteria in the culture. 

 

If there are any other live bacteria in the original milk or in the yoghurt, they will also grow, so this will affect the yoghurt that you get.  With raw milk there may be pathogenic (harmful) organisms in the milk that will also grow when the yoghurt milk is incubated. 


 




 

ACIDOPHILUS/BIFIDO YOGHURT

The production of cultured milk using starters Lactobacillus acidophilus and Bifidobacterium species is not often used as the sole culture in yoghurt.  More often they are added in with regular yoghurt cultures.  The acidophilus and bifidobacterium bacteria have been isolated from the human digestive tract.  They are claimed to have positive health effects on the human body.  Whereas the two bacteria for making yoghurt do not survive passage through the stomach and intestinal system, these bacteria do.  The benefits claimed by consuming this type of cultured milk include reduced flatulence, improved regularity and a positive effect on controlling harmful bacteria in the digestive system.
It is essential to maintain strict hygiene and cleanliness when making this product.  The milk takes about 30 hours or more to set because the bacteria grow very slowly.  If the milk becomes contaminated by other bacteria, the contaminants will probably grow faster than the starter spoiling the product.  To ensure sterile milk we suggest that you use long life (UHT) milk. 

 

ABT YOGHURT

The cultures used here are Lactobacillus acidophilus, Bifidobacterium species and Streptococcus thermophilus.  The yogurt gets its aBt tag from the names of the starters, (note the bold letters in each bacterial name).
This yoghurt is a safer process in that the fermentation takes around 8 hours instead of the 30 hours for aB yoghurt.  The shorter time means less chance of contaminant bacteria growing in competition with the aB cultures.  The down side is that the numbers of acidophilus and Bifido bacteria are diminished by the growth of the t (streptococcus thermophilus) culture.  If you want a good dose of aB cultures then this yoghurt will need to be cultured at 37-39°C.  It is essential to maintain strict hygiene and cleanliness when making this product.
As with all probiotic yoghurts, you cannot use this yoghurt as a starter for the next batch of yoghurt and get any significant amount of probiotic cultures growing. 

 


NOTES ON SOY YOGHURT.
Soy beverage or soy drink is not milk but a form of bean juice.  This means we are not able to use the traditional methods of making cheese.  We can however make yoghurt in much the same way as we make regular yoghurt, provided that a few of the basic conditions indicated below are met. 

Glucose levels

Soy beverage may need to have additional fermentable sugar (glucose) added to ensure fermentation.  If the soy beverage does not have glucose added (or has insufficient added) the cultures will not have sufficient food to grow.  In this case add 1% glucose powder or 2% glucose syrup. 

Protein levels

For a stirred Yoghurt the protein level should be 4 – 4.5 %.
For a set yoghurt the protein level should be 5.0 – 5.5%.
As with basic yoghurt making principles, lower protein levels may result in a weak or sloppy set.