Guest Columns

Perspective:
Dairy Research

The relationships you can’t put on a balance sheet

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®.

A longstanding, major issue across the cheese industry is the high risk or prevalence of calcium lactate crystals. These are small, white crystals that sometimes form on the surface of cheeses like Cheddar and even Colby. These crystals can look unappealing to consumers, and some might mistake these crystals for mold. Calcium lactate crystals can also be indicative of poor-quality cheese — these crystals often form on cheese that is too acidic, which negatively impacts flavor and texture. However, there are some consumers who like slight crystal formation and see it as an indication of a well-aged Cheddar.

These crystals are not new to cheesemakers. For more than 100 years, calcium lactate crystals on cheese have been noted in literature, but the risk of them forming has increased in recent decades. Industry practices have also changed, including the use of faster makes, fortification of milk, more aggressive starter cultures, higher salting pHs and accelerated ripening. Cheesemakers struggle with the fact that the formation of these crystals seems unpredictable — sometimes they appear and sometimes they do not.

The good news is that we now know more about the chemistry behind calcium lactate crystals and the factors that go into their formation on cheese. Two big factors that contribute to calcium lactate crystal formation are high levels of residual lactic acid in cheese, and moisture migration or sweating.

Let’s start with what is needed for these crystals to form. There needs to be sufficient levels of calcium and residual lactic acid in the cheese serum to develop calcium lactate crystals. Most Cheddar cheeses made today have more than enough calcium and lactic acid for the crystals to develop (for a cheese with a moisture content of 38%, there needs to be 0.235% calcium and 1.05% lactic acid in the cheese serum phase).

However, just because a cheese apparently has the right levels of calcium and lactic acid, doesn’t always mean the cheese will form crystals.

Over the years, many in the cheese industry shifted to using faster makes to speed up the cheesemaking process. Historically, most Cheddar cheese was made with bulk starter cultures instead of the direct vat frozen/freeze-dried cultures commonly used today. Bulk cultures allowed more acid to develop up front in the cheesemaking process, and thus more of the lactic acid was lost in the drain whey. Modern cultures are not fast acidifiers (once they become active); they can also result in lower-pH cheese. Some factories try to avoid a low final cheese pH by salting and hooping at a very high pH value. But this leaves less time for whey drainage and traps more whey in the cheese, which results in more lactose and lactic acid in the cheese.

Fortification of cheese milk with condensed milk, reverse osmosis concentrates or nonfat dry milk powder unfortunately also increases the initial lactose content (as lactose is around 50% of the solids in these materials). We recommend using ultrafiltration or microfiltration concentrates instead. An increase in the casein content of milk also increases buffering, which necessitates more lactic acid production by the starter to reach the target pH value. Preacidification (addition of acid) of cheese milk is recommended to help reduce the higher buffering in concentrated milk (acid addition helps with the solubilization of insoluble calcium phosphate, a key buffer).

Another next big step, or factor, that contributes to calcium lactate crystals formation is moisture migration. Most of the moisture in cheese is mechanically trapped within the casein network. However, several factors can cause moisture in cheese to move and pool on the surface of the cheese (this is sometimes called “sweating”).

Some of the factors that cause moisture migration include too low pH, too much salt and proteolysis in a low-pH cheese. If a cheese has a low pH (close to or less than 5.0), the casein network rearranges and creates more serum pools that can move more easily. High salt levels in cheese cause the proteins to contract, and serum is squeezed out of the protein network. Excessive proteolysis or protein breakdown weakens the casein network and releases previously trapped serum. Another cause of moisture migration in cheese is changes in temperature. If a cheese plant uses accelerated ripening, they hold the cheese at a warmer temperature for some period and then later restore the cheese to the normal lower temperature storage. The cheese matrix shrinks upon warming (holds serum less effectively) and the matrix expands again on cooling, which promotes moisture movement. In retail settings, cheese may be held at a higher temperature than used in the factory cooler, and this can lead to moisture migration.

Moisture migration is a significant factor in crystal formation because it causes some of the cheese serum to move from within the body of the cheese to the outside surface of the cheese, which is where calcium lactate crystals usually form. When a cheese sweats, moisture then evaporates, leaving a concentration of minerals on the surface. This process can continuously occur and therefore “feed” any crystals on the surface of the cheese. Basically, anything that promotes moisture movement is going to increase the chances of calcium lactate crystals forming on the cheese surface.

Other factors that contribute to calcium lactate crystal formation include loose packaging and rough cheese surfaces. Poor package to cheese contact (e.g., wrinkles, loose edges) creates surface sites where serum can collect. The serum evaporates into the headspace/package and provides sites for crystal growth. Vacuum packaging helps reduce the risk of poor package to cheese contact. It is difficult to control crystal formation in shingle stacked slices of aged Cheddar because it is impossible to get tight film contact to all surfaces of the sliced cheese. Rough or uneven cheese surface also creates more sites where serum can collect. This can be improved by optimizing cutting and slicing to reduce surface roughness. We’ve also found that smoked cheeses are at risk for crystal development because smoking dries out the cheese surface, concentrating the calcium lactate.

At the beginning of the article, I mentioned that most Cheddar cheese produced and sold on the market today probably exceeds the solubility level/limit for calcium lactate. So, the question is, why don’t crystals always form? Why do they only form some of the time? One explanation is the need for moisture migration to effectively promote surface crystal growth. Another key issue is that the soluble calcium in the cheese serum is also associated (complexed) with other soluble salts (anions) like phosphate and citrate. Therefore, there may be insufficient levels of calcium ions remaining to form calcium lactate crystals. Thus, the cheese serum may exist in a metastable supersaturated solution where calcium lactate remains soluble past its normal solubility threshold. All of these different factors result in a complicated balancing act where the cheese can easily be tipped in either direction and form calcium lactate crystals or stay clear.

If you want to learn more about the science behind calcium lactate crystal formation in cheese, I recommend Mark Johnson’s new book, “Cheese & Cheesemaking Explained Through Chemistry & Microbiology.” Johnson
spent most of his career in one way or another studying cheese crystals, and the book includes an entire chapter devoted to the topic.

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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