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Perspective:
Dairy Research

Increasing yield, efficiency with concentrated milks

John Lucey

John Lucey, director of the Wisconsin Center for Dairy Research at the University of Wisconsin-Madison, contributes this column for Cheese Market News®.

If you ask a cheesemaker what some of the qualities are that they look for in their milk, most will probably say high fat and protein and overall high-quality milk (low somatic cells, low microbial counts). To control cheese composition (such as, to meet legal compositional standards for cheeses), the dairy industry has developed different methods and technologies to standardize the starting milk.

These methods depend on the cheese variety and the desired fat and protein level required in the cheese. For instance, the target protein/fat ratio in Cheddar is around 0.9, so whole milk could be used, whereas for low-moisture part-skim Mozzarella, the ratio is around 1.4, so we can remove some fat or dilute the fat content in the milk with skim milk to achieve the desired protein/fat target. Removing fat from milk will reduce the yield of cheese produced since yield is directly related to the concentration of fat and casein in the cheese milk. Some plants will add concentrated milk (e.g., condensed skim) to achieve the appropriate casein-to-fat ratio in the cheese milk, and with this approach the solids content in milk increases, and so the yield increases, too.

If membrane filtration is used, the cheesemaker has the advantage that they can also adjust the lactose content in the standardized milk; unconcentrated milk contains around double the concentration of lactose needed for fermentation to achieve the target pH for many varieties. The commonly used membrane filtration technique ultrafiltration (UF) concentrates both the casein and fat in milk but removes some lactose. The permeate from ultrafiltration can be subjected to nanofiltration, and the permeate can be used for lactose dilution (adjustment) in the milk (since it does not contain lactose, only water and monovalent salts), thus eliminating the need to add groundwater to the milk. Lactose standardization of the milk also avoids the need for curd washing or whey dilution techniques during the cheesemaking process used for certain varieties such as Gouda and Colby. Lactose standardization would be a big step forward for cheesemakers because it would allow them to standardize lactose content that is needed for a particular product to obtain the desired pH. If there is too much lactose in the initial milk, then the cheese can be acidic and/or it can result in defects like the formation of calcium lactate crystals.

Another issue with making consistent cheese is related to changes in milk composition during the year.

Changes can be due to seasonal, lactational or dietary effects. As I write this column, we are heading into the summer months here in Wisconsin and, as the weather warms, the protein content in milk often begins to drop. Protein, in particular casein, is crucial to the cheesemaking process, and milk with lower casein content will negatively impact coagulation and cheese yield.

Standardizing the casein content of milk with microfiltration (MF) is now common in Europe as this allows for the more direct and explicit control of coagulation and yield. Microfiltration has not been approved for use in the U.S. for cheesemaking. The use of MF of milk also has the benefit of creating a novel coproduct called milk-derived whey, which has minimal fat and improved flavor and clarity over traditional whey. Additionally, since it was not obtained from the cheesemaking process, it does not contain colors, enzymes or starter cultures.

When membrane filtration is performed within a plant it has been considered another pretreatment of the cheese milk and just an alternative way of producing cheese with the same composition and quality as traditional products that do not use this pretreatment step. For cheesemakers purchasing UF milk for use in their plant, FDA has issued an enforcement discretion allowing its use in cheeses with standards of identity (UF milk has always been allowed in non-standard cheeses). Hopefully, we will see a final rule issued soon by FDA that will modernize its standards and bring the U.S. into line with the rest of the world by allowing all types of liquid membrane concentrates in cheese.

Increasing the solids content in milk also has the significant benefit of increasing the yield of cheese. For example, if we were making a 37% moisture Cheddar cheese from milk with 2.5% casein and 3.2% fat, we expect a cheese yield of about 9.4% (i.e., 9.4 pounds cheese from 100 pounds of milk), and if we double the concentration of the casein and fat in the cheese milk by using membrane filtration, we should also double the yield to about 18.8% (assuming we have a similar cheesemaking process). For a cheesemaker, using concentrated milk results in obvious economic benefits like higher cheese yield, increased production per day and could reduce the immediate pressure for a plant expansion if sales were rapidly increasing.

A key aspect to keep in mind is that if there are more solids in the cheese vat, there needs to be adequate curd handling equipment downstream because there will be more curd coming through the process. For instance, larger or more drain tables might be needed, and for Mozzarella, key equipment like a cooker/stretcher might not have sufficient capacity to handle in a tumult fashion a larger volume of curd (delays in processing of curd would likely result in variable quality cheese due to differences in pH).

One issue with using concentrated milks is that the rennet coagulation process will be impacted if the casein content is greatly increased (e.g., greater than 3.0%). Since there is more casein in the milk, once gelation occurs the rate of increase in curd stiffness will be rapid. This means precise control of the cutting time is very important. In an enclosed vat this can be difficult because we can’t easily see the formation of the coagulum.

When using concentrated milk in modern cheese vats, my recommendation is to cut the coagulum while soft, and cut quickly. This will result in lower moisture in the cheese but greater fat recovery and less fines. Other protocols can be used to produce a higher moisture content in the cheese. Another strategy is to reduce the vat or set temperature, which will slow down coagulation and make it easier and allow more time for proper cutting. When using concentrated milks, it is also common to preacidify the milk, because more of the insoluble calcium needs to be removed from concentrated milks; otherwise, the final cheese tends to be tough or curdy or not melt properly. Where to get these concentrates? Plants can produce their own membrane concentrates in-house (from their own milk) or purchase concentrates (whole or skim milk) from suppliers.

One last thought on this topic is: How far up in concentration of cheese milk can we go? Part of the answer depends on what kind of cheese vat is being used and, specifically, how the curd is cut in the vat. Each vat design has its own way of cutting the curd. For instance, think of a large horizontal vat; it can be hard to complete cutting before the curd firms so fast that it just clumps together in a firm mass. The key here is to use faster revolutions to quickly curd the coagulum and form our curd particles. One thing to keep in mind is that we should always be monitoring the level of fat in the whey — if we’re not cutting properly (right time/speed), there will be a lot more whey fat generated due to tearing of the curd particles. Here at the Center for Dairy Research, we’ve been exploring how to make cheese with high solids milk. The question we’re interested in is, what is the upper limit? Is it 5% casein, 8% or even 10% casein? We don’t have a final answer yet, but we have successfully made cheese from 8% casein milk. To go much higher in casein content we may need to reimagine the cheesemaking process and maybe skip cheese vats altogether in favor of a more continuous process. But that is a thought for another day.

I would suggest cheesemakers that are not currently utilizing concentrated milks to investigate this option.

Reach out to CDR staff for advice. Using concentrated milks, cheesemakers can successfully adjust their recipes to continue to make high-quality cheese while gaining important benefits like greater yield and higher plant efficiencies.

CMN

The views expressed by CMN’s guest columnists are their own opinions and do not necessarily reflect those of Cheese Market News®.

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