Cheese making from ultra filtered milk

Terms and Principles

See Figure 5.1 and Membrane Processing in the Dairy Science and Technology Education website.

Reverse Osmosis (RO).

A pressure driven process where small molecules (molecular weight less than 100 daltons, eg., water) are separated from larger molecules by a semi-permeable membrane. In practice the term describes a concentration process where water is removed to increase total solids content of a liquid. For example desalination can be accomplished using (RO). It is appropriate to think of RO and the related membrane processes, UF and nanofiltration, as chemical filters where the separation characteristics are determined by the pore size of the membrane and the chemical interactions between the product and the membrane. The most common RO membrane material is cellulose acetate with operating pH of 5 -7. Dairy applications include supplementation of milk evaporators, whey concentration, and waste treatment.

Ultra filtration (UF). 

A membrane process similar to RO where semi-permeable membranes are used to separate large molecules (molecular weight greater than 10,000) such as proteins from small molecules such as sugars. Common membrane materials are polysulfone (operating pH 2 - 12) and ceramic (pH 2-12, retort sterilizable).

Nanofiltration. 

A membrane process with separation characteristics intermediate between RO and UF. It is designed to separate small minerals and ions from larger molecules such as sugars. It is used to demineralize cheese whey as an alternative to ion exchange and electrodialysis processes.

Microfiltration. 

A membrane filtration process designed to separate particles greater than .2 µM. Principal dairy applications are spore removal from milk to prevent late gas defect in cheese and to extend the shelf life of pasteurized milk.

Permeate and Retentate. 

Material passing through the membrane is permeate while material retained by the membrane is retentate. For example UF milk permeate is composed of water, sugar, some minerals and non-protein nitrogen compounds. UF retentate is a concentrate of milk fat and protein, including both caseins and whey proteins.

Component processing. 

Developments in membrane processing combined with other conventional and emerging technologies make it possible to isolate and recombine milk components in new ways to produce new products, process conventional products more efficiently, or reduce waste.

Benefits of UF in the Dairy Industry

Countries most active in the study of the properties and processing of UF milk retentates are France, U.S.A., Holland, England and Australia. The earliest and currently the largest dairy application of UF is in the production of functional (i.e., undenatured) whey protein concentrates. Reverse osmosis is also used in whey processing.

Potential benefits of membrane processing are:

Reduced Farm Feed Costs. Permeate which could be removed at the farm contains lactose, minerals and some nitrogen.

Cheese Manufacturing Costs. Reduced cooling and heating costs, lower rennet needed, reduced capital equipment costs, and increased yield from better retention of whey proteins in the cheese.

Transportation Costs. On farm UF would reduce milk volume by a factor of at least 2, and UF-thermized milk could be picked up less frequently

Economic Benefits to the Farmer of performing UF on the farm, are savings in both transportation and feed costs and the opportunity to market a value added product.

Product Standardization. It is possible to standardize the protein, fat and non-fat solids of all dairy products. For example fluid milk is now skimmed to a legal minimum of 3.25% fat so that on average about 6.0 kg of fat is removed per 1,000 kg of milk. UF makes it possible to skim protein in the same way as we now skim fat. This practice will be increasingly attractive as the value of milk protein relative to milk fat increases.

New Products. New cheese varieties, dairy spreads, high protein milks, milk based meal supplements. 

Properties of UF Milk Retentates

Composition. 

UF retains all milk fat and protein. Lactose permeates freely through the membrane. Mineral retention is dependent on the association with proteins and decreases with acidification.

Physical Properties. 

Fat globules are slightly reduced in size, indicating that some homogenization takes place in the UF system. Casein micelles and whey proteins are unaltered. Buffer capacity of UF retentates increases exponentially with total solids due to the concentration of proteins and salts

Lactic Fermentation.

Culture growth is normal but more acidity is required to reduce pH because of the high buffer capacity of UF milk retentate..

Rennet Coagulation. 

If rennet is added proportional to milk volume rather than weight of protein, rennet coagulation time (RCT) is unaffected by UF concentration. This means that, relative to the amount of protein present, less rennet is required for coagulation. However, the structure and properties of the gel are quite different than in normal milk, and for aged Cheese there is insufficient rennet to promote ripening. Concentration by UF has the remarkable effect of restoring rennetability to over pasteurized milk.

Milk Quality.

UF activates the natural milk lipase and concentrates bacteria. However, UF retentates have superior freeze-thaw stability, less oxidative rancidity, and have greater microbiological stability.

Development of UF Applications in the Cheese Industry

MMV Process. (Maubois et al., 1969) Concentrate to 5 - 7 x original milk protein content, add both starter and rennet, incubate until both coagulation and lactic fermentation are complete, and ripen. MMV is most successful for some fresh and soft-ripened cheese varieties which have relatively low total solids and do not require rigorous pH control. It has been most successful for Feta cheese. The chief difficulty is that the MMV process produces close textured cheese which has led to two types of Feta: (1) Structured or conventional Feta and; (2) UF or cast Feta. The MMV process can also be used to manufacture cheese base to extend young Cheddar in process cheese formulations. The amount of UF retentate in process cheese products is limited by the presence of whey protein in the retentate which impairs meltability of the cheese.

The LCR Process. LCR stands for low concentrated retentate. Milk is concentrated 1.5 - 2 x original milk protein content. Cheese is made using minor modifications to traditional procedures. LCR is now the principal process used in French Camembert providing the advantages of slightly higher yields, labour savings, facilitation of continuous cheese making, and increased plant capacity. Most types of hard cheese have been made by LCR principles with varying degrees of success.

UF retentates in the mid range of concentration (2 - 5 x original protein content) have not been successful with the possible exception of Feta. It is possible to produce higher yields of Feta than via conventional means by heat treating retentate at sufficient levels to denature whey proteins. Normally this would impair rennet function, but UF treatment restores rennetability. The result is that denatured whey proteins are incorporated into the rennet gel, thus increasing cheese yield. This permits manufacture of a structured Feta, similar to traditional products, while realizing significant yield improvement. This practice has been successful for Feta but not for most rennet cheese because the whey proteins impair meltability and produce a coarse textured cheese.

TABLE 22.1 Ultrafiltration of whole milk. Typical composition of concentrate and permeate System: polysulfone membrane in tubular configuration, small pilot plant, batch operation at 50C (Glover, 1985).

 polysulfone membrane in tubular configuration, small pilot plant, batch operation at 50C