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Dairy Ingredients Q&A

Have you ever wondered what causes water/moisture to form on the surface of butter? Or why it’s difficult to melt mozzarella that was previously frozen? The answers to these questions, and many others, are in this section of MILKingredients.ca.

>>> Perhaps one of the following topics is just the one you are looking for:

1. What causes water/moisture to form on the surface of butter?

2. Is there a difference between butteroil and ghee?

3.
Why is cellulose used in shredded cheese?

4. What causes cream that has been frozen to separate when thawed?

5.
What causes water to form in cream cheese?

6. In what way would lactoglobulins added to a cheese formulation change the taste of the final product?
7. What is meant by the description: Modified Milk Ingredients?

8. Why is it difficult to melt mozzarella cheese that was previously frozen?

9.
Why does separation occur in sour cream that has been previously frozen?



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1. What causes water/moisture to form on the surface of butter?


Butter is a water-in-oil emulsion produced from cream. When cream is churned, the partially crystalline fat globules cluster to form a network. The result is the breakage of the oil-in-water emulsion structure of the cream and the formation of distinct butter grains with the release of much of the water component of the cream, known as buttermilk. The butter grains are salted and worked to produce a continuous mass of butter that contains a moisture content of 16% within the system in the form of finely dispersed droplets. Separation of this moisture from the butter can occur as a defect commonly referred to as "leaky butter".

The separation of water from butter is strongly related to the size of the water droplets within the oil network. The larger the water droplets are, the greater the likelihood of their association, eventually leading to development of the "leaky butter" effect. Churning of the butter is the critical processing step related to proper water incorporation. When the butter is churned, the butter grains are consolidated while the water present is divided into fine droplets that become dispersed in the oil network. If butter is not adequately churned, then the resulting water droplets will be larger than optimal and prone to coalescence. Inadequate churning is possible if the churning time is too short or if the churn is overloaded with material. Also, if the butter grains are too soft at the start of the churning process, they will mass together quickly and will be unable to offer the resistance needed to break up the water droplets. The softness of the fat is dependent on factors such as the temperature and seasonal variations in the composition of the fat.

Improper working of salt through the butter can also lead to the "leaky butter" effect. If the salt is not mixed through, an osmotic gradient can be formed causing moisture to migrate through the butter to the areas where the salt concentration is the highest. This localization of the water will cause the coalescence of the water droplets and increase their size.

Handling of the butter during packaging can also impact water separation. The butter emulsion is a somewhat delicate system with the water droplets dispersed inside the oil. If the shear forces applied to the butter during handling are too large then the droplets of the aqueous phase can come into contact and combine with one another. Handling of the butter should either be very gentle, or else designed to promote re-emulsification (for example a high shear inline buttermixer).


By Kevin Segall, Ph.D., Research and Development Scientist, and Nathan Payne, B.Sc., Research Scientist and Packaging Specialist, Guelph Food Technology Centre.


2. Is there a difference between butteroil and ghee?

A popular product in India and in Egypt, ghee is made from milk, but can also be made from cream or butter. Bacterial cultures like lactobacilli or streptococci are added to milk to develop unique flavours; this stage is sometimes called maturing. After maturing, the product is heated for several hours above 100°C and the filtered and cooled. The heating step drives off the water and denatures the whey proteins. The filtering step removes the whey proteins and results in a finished product that is mainly fermented butteroil with less than 1% water.

Ghee sometimes has a slightly brown colour due to the Maillard reaction that occurs during heating.

Butteroil is a term used for pure fat that is extracted from milk than can be made from cream or butter. The emulsion is destabilized by heat and/or by agitation and the oil is then separated by centrifugation. Air is then removed and the oil is dried in a vacuum dryer to remove additional moisture.

The important differences between ghee and butteroil remain in the manufacturing process, their finished flavour, their colour and their texture.


3. Why is cellulose used in shredded cheese?

Shredded cheese is mechanically shaken with a small amount of cellulose, prior to packaging. The sole purpose of adding this ingredient is to prevent the cheese shreds from sticking together and forming clumps.


4. What causes cream that has been frozen to separate when thawed?


The key factor in determining how the cream survives freezing and thawing is the size of the ice crystals. The larger the ice crystals are, the more damage they do to the surface coating of the fat globules. Stabilizers included with the whipping cream can bind water. As a result, not as much water is available to participate in ice crystal formation. The ice crystals formed are smaller, which allows the fat globules to retain their surface coating. When the cream is thawed, the fat remains as distinct globules and the cream can be whipped. Whipping cream without stabilizer can be frozen and remain functional if the cream is frozen very rapidly using special equipment. The faster the cream is frozen, the smaller the resulting ice crystals and functionality is preserved for the reasons explained below.

Background Information

Whipping cream is an oil-in-water emulsion containing 35% fat in the form of individual globules. Because whipping cream is not a homogenized product, the fat globules are the same size as those found in whole milk and are still coated with the native fat globule membrane proteins. When the cream is whipped, not only is air introduced into the system, the shearing action promotes collisions between the fat globules and also damages their protein surface coating. These factors promote the conversion of the individual fat globules into a three dimensional network. The network of fat formed upon whipping gives body to the whipped cream and also helps to retain the air bubbles.

When pure whipping cream is frozen, much of the water in the system is converted to ice crystals. Close association of the fat globules with the ice crystals may physically remove some of the membrane coating from the surface of the globules. Without the membrane coating for protection, the ruptured fat globules can easily merge with other fat globules. As well, conversion of the water to ice concentrates the fat globules, bringing them closer together and increasing the likelihood of interactions. These factors result in a loss of the emulsion structure upon thawing. The thawed cream is therefore separated with the majority of the fat floating on top of the water phase. Because most of the fat is now present in very large particles, the proper fat network cannot be established when the cream is whipped. Without the proper fat network, the cream cannot stabilize the air bubbles and so the amount of air incorporated is much poorer. Although it cannot be used for whipping, the separated cream can be used in products such as "cream soups" where flavour is the critical factor or in products such as ice cream where homogenization is part of the manufacturing process.


By Kevin Segall, Ph.D., Research and Development Scientist, Guelph Food Technology Centre.


5. What causes water to form in cream cheese?

Syneresis occurs when proteins in the cheese gel network become too highly associated, preferring to interact with each other, rather than with water. The result is a shrinking of the protein network and the expulsion of serum from the gel. Such a situation occurs if the pH level of the cream cheese is right at 4.6, the isoelectric point of the casein molecules. At this pH level, the charges on the proteins are balanced, resulting in a condition that promotes protein-to-protein interactions and thereby minimizes the proteins’ ability to retain water. This problem can be overcome by lowering the pH level of the cheese to just below 4.6. This will result in an overall charge on the proteins and will prevent them from becoming overly associated.

In addition to controlling the pH, syneresis can also be discouraged by incorporating ingredients into the cream cheese that have water binding properties. For example, polysaccharide gum-type stabilizers are commonly used in cream cheese formulations to function as a thickener and to help retain water within the protein gel network. The type of stabilizer and the level of usage are factors that can be manipulated to counteract syneresis.

Another similar means of countering syneresis is to increase the protein content of the product. Casein proteins added through skim milk powder or caseinate can contribute to the gel network and help retain water. Whey proteins added as part of skim milk powder or as a whey protein powder will also hydrate and help thicken the serum phase.

Background Information


Syneresis is a phenomenon in which serum (water plus dissolved components) is released from a protein gel network. The development of this condition during cheese storage is highly undesirable because it is detrimental to the visual characteristics normally associated with the product. Cream cheese, in simple terms, is a cheese that is formed by the acid precipitation of homogenized, high fat (12-16%) milk) and is a product prone to syneresis during storage.


By Kevin Segall, Ph.D., Research and Development Scientist, Guelph Food Technology Centre


6. In what way would lactoglobulins added to a cheese formulation change the taste of the final product?

Cheese flavour develops as a result of the breakdown of protein and lipid components in the curd during ripening. The longer the cheese is aged, the longer these reactions proceed, resulting in a stronger flavour. Lactoglobulin is the predominant protein in whey. Incorporating whey changes the flavour of the cheese by altering the pattern of protein breakdown. In addition, when the whey is incorporated by high heat treating the milk, some of the enzymes responsible for normal flavour development are de-activated. Ripened cheeses made to incorporate whey have been described as having weak, sour or bitter flavours. Whey incorporation has typically been found to be most successful for fresh cheeses (cheeses that are not aged).


Background information

In traditional cheesemaking the casein proteins are coagulated to form the curd and the whey proteins are lost with the whey. Because the casein proteins only represent 80% of the total protein in milk, 20% of the available protein is not used in the traditional process. Therefore, cheese manufacturers have been looking for ways to incorporate whey proteins into the curd to improve both the yield and the nutritional value. Incorporation of whey into cheese can have a significant effect on the sensory attributes of the cheese, including the flavour.

There are three main technologies for incorporating whey into cheese:
  • Exposing the cheesemilk to heat treatment more severe than pasteurization. This treatment will unfold the whey proteins and allow them (principally lactoglobulin) to bind to kappa casein on the surface of the casein micelles. The whey proteins that are physically attached to the caseins become part of the curd when the coagulation process occurs.
  • Adding denatured and aggregated whey protein to the cheesemilk. When this cheesemilk is coagulated, the resulting curd incorporates the small particles entrapped within the curd matrix. This sort of addition can be beneficial to the texture of low fat cheeses.
  • Ultrafiltration of the cheesemilk to remove much of the water and small molecule components. Coagulation of the resulting "precheese" gives a curd that does not release much, if any whey.

By Kevin Segall, Ph.D., Research and Development Scientist, Guelph Food Technology Centre.


7. What is meant by the description: Modified Milk Ingredients?

The term "Modified Milk Ingredients" can be used on a product label where the formulation call is for a blend of a dairy by-product (such as whey) with a milk-based ingredient (such as skim milk powder/whole milk powder.) Rather than list the ingredients separately, the manufacturer is able to use this generic description which also allows for changes to be made to the dairy formulation at a later date without having to re-do the label information on the packaging material. In this scenario the product has been "modified" by mechanical means.

The use of the term "Modified" in this case should not be confused with the term "Genetically Modified Organism" (GMO) which involves a product/ingredient for which the composition has been altered chemically or genetically from its original form.


8. Why is it difficult to melt mozzarella cheese that was previously frozen?

Mozzarella cheese is quite perishable due to its high moisture content, and as a result it is desirable to store the cheese in a frozen form. However, once thawed the functionality of the mozzarella may suffer, including poor melting behaviour characterized by reduced flow and increased oiling off. The problems with flow are related to the distribution of water within the cheese and can be combatted by thawing and holding the mozzarella at refrigerator temperatures for 1-3 weeks. The increase in oiling off may be due to a reduction in the ability of the cheese proteins to bind fat. The molecular changes caused by freezing and thawing and their impact on the melting behaviour of mozzarella cheese are discussed in more detail below.

Background Information

All cheeses are essentially casein protein networks with entrapped fat globules and water (which contains dissolved salt and other soluble components). Heating cheese will soften it by melting the fat crystals present. Whether the hot cheese flows or not depends on the characteristics of the protein network, as strong association between proteins will inhibit flow. The key factor affecting the protein network, in regards to frozen mozzarella is the hydration of the proteins.

Most of the water in cheese can be classified as either expressible water, which can be mechanically "squeezed" out of the cheese or entrapped water, which is retained by the protein network. As a cheese is stored the protein network absorbs increasing amounts of water and the amount of entrapped water increases at the expense of the expressible water. When the protein network becomes highly hydrated, some protein-protein interactions are replaced by protein-water-protein interactions. This type of network, "lubricated" by water is better able to flow. When cheese is frozen, water molecules cluster to form the ice crystals and are taken away from the protein molecules. As a result, the proteins become less hydrated and forced into more protein-protein interactions. Thawing of frozen cheese converts the ice crystals back into liquid water but does not instantaneously redistribute the water molecules throughout the protein network. Instead this water exists as tiny localized pools. Over time the water will be reabsorbed into the protein network and the melting properties of the cheese should improve. As a result, if possible, frozen mozzarella should be thawed and stored in the refrigerator for 1-3 weeks to give the best possible melting behaviour.

More free oil than expected may also be seen when previously frozen mozzarella is melted. As mentioned above, the protein network in mozzarella cheese surrounds the fat globules and water molecules. When the water is frozen to form ice, interaction between the ice crystals and fat globules seems likely given their close association. It is possible that the growing ice crystals may rupture the fat globules and promote their interaction to form larger fat aggregates. If the casein network cannot emulsify these larger fat particles (some protein damage may also result from freezing), then more free oil will be seen when the cheese is melted.


By Kevin Segall, Ph.D., Research and Development Scientist, Guelph Food Technology Centre.


9. Why does separation occur in sour cream that has been previously frozen?


Sour cream is prepared by acidifying homogenized cream with culture microorganisms. Lowering the pH level causes the interaction of casein proteins and the development of a weak gel structure throughout the sour cream. This gel structure consists of many small protein-coated fat droplets that are cross-linked by casein proteins. Entrapped within this fat and protein network is the serum phase, consisting of the water fraction of the product along with small dissolved compounds like salts and sugars. This serum phase exists in small areas, separated from each other by the gel network.

When the sour cream is frozen, the water is converted into ice crystals and the sour cream expands in volume. As the water is highly compartmentalized, its expansion upon freezing results in physical disruption of the protein-fat network. Damage to the linkages in the gel weakens the gel structure and allows contact between formerly discreet areas of water. When the product is thawed, the ice crystals are converted back into water and the formerly small clusters of water molecules are able to pool together. The damaged gel structure is unable to hold these larger pools of water and the result is separation of the cream.

In whipping cream, freezing causes separation by physically damaging the surface of the fat globules, allowing the fat particles to join together upon thawing. Adding stabilizers to whipping cream can greatly reduce this freeze damage by inhibiting ice crystal formation. Sour cream formulations typically include stabilizers that discourage ice crystals from forming. However, separation still occurs when sour cream is frozen and thawed because the sour cream gel structure is very easily damaged, and even small ice crystals are capable of disrupting the network which holds the serum phase.


By Kevin Segall, Ph.D., Research and Development Scientist, Guelph Food Technology Centre