Last month we looked at the impact of changing moisture in mozzarella type cheeses. This month we will discuss two other key functionality of mozzarella – browning and free oil formation.

Browning

Browning occurs when unfermented milk sugars react with some amino acids and peptides during heating. Although some browning is required the extent required differs between customers and thus needs to be controlled by the manufacturer.

Browning can be affected by

1. Starter culture – Traditionally, a mix of S thermophilus and Lb bulgaricus has been used to make pizza cheese. Substituting the Lb bulgaricus with Lb helveticus has been shown to be effective in reducing browning because of its ability to ferment galactose. Depending on your customers preferences you can vary the degree of browning by varying the mix of Lb bulgaricus or Lb helveticus in the mix. Your starter culture rep should be able to help with this.
2. Age - As cheese matures the level of browning tends to increase.
3. Washing - Washing curd with warm water removes some lactose resulting in less browning.
4. Salt and moisture - Browning also follows excessive blister formation during cooking. Low moisture and high salt in cheese will lead to high blister formation.

Free Oil formation

Free oil formation is an issue when large pools of oil form on the top of pizza during cooking. This is unsightly and not pleasant to eat.  Free oil can be controlled by the following:

1	Fat content or more precisely fat in dry matter Fat in Dry Matter FDM = Fat (100-moisture %) As FDM goes above 40% e.g. 23% fat, 45% moisture than free oiling will increase
2	Salt content. As salt content deceases then free oil increases, thus if you want to make a higher FDM product then you may need to add extra salt or increase brining time to reduce the free oil.
3	Proteolysis -  Excessive protein breakdown can also lead to free oil formation. Excess proteolysis can be caused by some highly proteolytic rennets or starter cultures, particularly if stretching temperatures of less than 60°C are used. Storing pizza cheese at high temperatures will also accelerate ripening and lead to more proteolysis.

Mozzarella is a Pasta filata type of cheese (Pasta filata is Italian for spun paste or stretched curd)

There are two main types:

1. Traditional Mozzarella

Made originally in Italy, this mozzarella is traditionally made from Buffalo milk and has 48-52% moisture.  This type is made in Australia from cow’s milk and tends to be softer than the mozzarella made for food service and is sold in block or traditional shapes, e.g. pears or plaits. There is normally no draining or cheddaring belts used and the cheese is predominantly brine salted.

2. Mozzarella Cheese for Food Service

This type of mozzarella cheese is a rennet coagulated semi hard cheese variety with a composition range from 45 -52% moisture and 30-50% fat in dry matter. It is predominantly used for pizza toppings and is sold either shredded or grated. It is often made in traditional cheddar plants using cheddaring belts and may include a dry salting step.

As Mozzarella is predominantly used in pizza toppings the main quality attributes relate to functionality once the cheese is melted eg, texture, look and feel. This article will review the impact of moisture variation on the functionality of mozzarella cheese.

Impacts of higher moisture

Negative Impacts

• Proteolysis (i.e. breakdown from long chain proteins to short chain peptides), as moisture levels increase then the rate of proteolysis increases, which results in a more rapid breakdown of the cheese body. This means that the cheese becomes gummy earlier and will not shred as well.
• Increased browning
• Softer cheese body
• Increased potential for shreds to matt back together
• In low moisture mozzarella cheese an extra 1% moisture may reduce the shelf life by 1 month

Positive Impacts

• More cheese i.e. greater cheese yield
• Increased stretchability, flowability
• Less chewy
• Shorter ripening time

Manufacture Time

The longer the make time the greater amount of syneresis (moisture removal from the curd) and thus lower moisture at the end (assuming all other controls such as temperatures, stirring speeds etc. remain constant).  Faster acid production before draining and particularly before rennet addition will assist the cheese to retain more moisture.

Cooking/Cheddaring Temperature

Lowering the cooking and cheddaring temperatures will slow acid development and thus increase moisture levels. However this will also result in an increased make time to reach the final desired pH. Therefore extra starter may need to be used so that the make time remains the same.
Curd Washing

Some manufacturers wash the curd on the draining belts. This will result in extra moisture retention. Generally the lower the wash temperature the more moisture is retained.  Some manufacturers wash as low as 10°C. Again however to maximise the impact then other factors will need to be controlled so that the make time remains similar, e.g. increased starter or increased prime time before renneting.

Next issue we will look at control of other functionality issues such as browning. Note for more information on Mozzarella functionality control refer to Cheese Problems Solved edited by P.L.H. McSweeney

In the early part of my career I was employed at various times as a bulk starter culture maker, cheese maker and laboratory technician. I learnt very early the dread words, “the starter is going slow it must be a phage attack” I can remember many times as a lab tech getting ready to go home and being brought whey samples by the cheese factory manager saying “start a Pearce test on these please”, starting the test and then either he or me coming back 6 hours later to read the results.

So what are bacteriophages and how can we prevent them having a serious impact on cheese making?

Bacteriophages are a virus that attacks a specific strain of bacteria. Their mode of action is to inject their DNA into a living cell. The phage then replicates itself and the cell then bursts releasing a number of phage, these then attack many other cells. The result is that the phage multiplies much more rapidly than the bacteria being attacked. The resultant impact on cheese making is that acid production capacity is greatly reduced. This can result in no acid production at all (a dead vat) or poor quality low acid cheese.

Prevention

1. Hygiene, phage can only grow when they have a food source, therefore it is essential to regularly hose whey off the floor and remove spilt curd. Regular sanitising of the floor also will help.
2. Limit personnel access from raw milk areas to pasteurised milk. Phage will be present in raw milk but are destroyed by pasteurisation. Do not allow tanker drivers into cheese making areas. Ensure footbaths from raw to pasteurised areas are cleaned and refilled with sanitising solution regularly.
3. If making bulk culture limit entry of personnel to the bulk culture area. Maintain this room in an immaculate condition.
4. Starter selection

• Bulk Culture; ensure cultures used in a rotation are not phage related. Have a rotation of either 2 or 3 cultures or groups of cultures that have different phage relationships.
• Conduct activity tests daily to check if phage is building up, activity tests can detect low levels of phage enabling changes to be made before the acid production is slowed in the vat.
• Direct Vat cultures, 
  • Undefined cultures, these mixes have a large range of cultures that may vary slightly from batch to batch, because of the large number if 1 strain is attacked by a phage there is plenty of acid production still available from the other strains.
  • Defined cultures. These contain a smaller number of selected strains which makes them more susceptible to a phage attack; it is recommended that different strains are used in rotation.

Maturation of cheddar is affected by many factors. Some key ones are:

Initial milk quality. The quality of the milk as it enters the vat will have a large impact on cheese maturation. Milk breakdown commences as soon as the cow is milked. This breakdown leads to enzyme production. Some enzymes, particularly those produced by psychrotrophic bacteria can lead to unpleasant stale flavours in cheese. If milk quality is excellent than a more consistent cheese can be produced.

Starter selection, traditionally Lactococcus lactis and cremoris strains were used. These produce a clean typical cheddar flavour but often require long maturation times to develop exceptional flavours. Most bulk starter cultures for cheddar are still composed of these. However many direct vat cultures contain a wider variety of species and strains which will develop flavours more rapidly. Starter selection will influence the flavour and character of the cheese

Adjunct use. Adjunct cultures are added to impart particular flavour characteristics. They do not contribute to acid development during cheesemaking.  This allows product differentiation and also more rapid flavour development. Popular adjuncts include Lactobacillus helveticus and Lactobacill paracasei

Storage temperature.  I have seen cheddar stored between 2 and 12°C. The lower the temperature the slower the maturation. Cheddar in the US is sold at up to 7 years of age. This would have been made with low moisture and low storage temperatures. This produces very clean cheddar flavour. Maturing at higher temperatures, 9-12°C may lead to development of other flavours such as “fruity” which are favoured by some customers.

NSLABs. Non-starter lactic acid bacteria (nslabs) are those bacteria that are indigenous to the factory environment and enter the cheese from equipment, surfaces, walls and operators. If the same milk and starter was used in different factories the cheese would be different because of the NSLABs. Maintaining excellent hygiene standards will control the nslabs and thus lead to a consistent product. NSLABs may contribute to a depth of flavour which sometimes may be missing from cheddar produced in modern very hygienic plants. This depth of flavour can be attained by the careful selection of starters and the use of adjunct cultures.

How to prevent viruses attacking bacteria.

Phage are viruses that attack bacteria. The phage injects their nucleus into a living cell. This then reproduces in the cell until the cell burst, releasing up to another 20 virus particles. Virus’s thus multiply much more quickly than the starter bacteria. The result is either reduced or no acid production. When there is no acid production it is referred to as a “dead vat”. This is the last thing that a cheese maker wants to hear! Reduced or no acid production will produce cheese that is either inferior at best or virtually unsaleable and may be a potential health risk. The high pH will allow Staphylococcus aureus to grow if present and produce a pathogenic toxin.

Indications of phage presence

• A gradual reduction in acid production during a day’s manufacture either at whey off or later in the process.

• Higher than normal 24 hour pH.

Prevention

• Phage can build up in the environment. To prevent phage attacks consider the following:

• Maintain excellent hygiene in the vat room.

• Clean up the curd off the floor and equipment regularly.

• Don’t leave it until the end of the day.

• Don’t leave pools of whey on the floor.

• Minimise the entry of people from raw milk areas.

• Rotate cultures - use different strains every few days.

Phage are specific to a starter strain. e.g. when making cheddar cheese, Lactococcus lactis ssp cremoris is the bacteria primarily used for acid production. However there are numerous strains, or variants of this culture that are offered for sale by starer culture companies. Each strain may produce acid at a slightly different rate. Starter strains are combined so that phage unrelated groups are used together. Therefore if one strain is attacked by phage the other strains in the mix should still produce enough acid to enable cheese to be made. Rotating cultures means that the “problem phage” does not have a host to grow on and thus numbers reduce to inconsequential numbers.

Shamrock Food and our culture partner, Sacco, can provide tailored culture products to reduce the risk of phage attack in your plant. For specific advice contact Wayne either This e-mail address is being protected from spambots. You need JavaScript enabled to view it or phone 0407 667 435.