From the appearance to the flavor profile, enjoying cheese is a wonderful sensory experience. As such, manufacturers work hard to meet the flavor, texture and visual expectations of customers, but visual defects can detract from the premium image of cheese. Though visual defects such as pinking are not a safety issue, they can deter customers and cause significant issues for the industry. Therefore, understanding the cause of visual defects and prevention methods is essential to upholding the premium image of the dairy industry.

Preventing loss of color

In terms of visual defects, a loss of color pigment is one of the most common issues in the industry. Though milk itself is generally white, or perhaps a light yellow tone if the cows are grass-fed, many cheesemakers add annatto or another colorant to the cheese to create the orange color that many customers have come to expect from a cheese such as Cheddar. Derived from a plant and utilized for centuries, annatto has proven to be a safe and effective colorant, but visual defects such as pinking or bleaching are common when the annatto begins to lose its pigment.

This loss of pigment occurs due to oxidation, which is caused by the harsh lighting of the supermarket shelves. Studies show that pigment loss can occur within just a few hours if the cheese is exposed to high-intensity fluorescent light (> 160 footcandles). The pigment loss will generally present as a pink tone but if the cheese continues to be exposed to intense lighting, a complete loss of pigment is possible which can lead to bleaching.  While the color loss itself does not affect the flavor, it might indicate that the fat molecules in the cheese have been oxidized, which will likely result in flavor defects.

Additionally, intense lighting can also cause warming of the cheese, potentially leading to other issues like sweating or crystal development. In other words, pinking and bleaching are warning signs of a quality issue. At this time the best way to avoid this issue is to use packaging with a light blocking material. Some studies suggest that LED lighting, which is a growing trend in retail display cases, might reduce exposure to UV radiation and heat. 

Issues with pinking

In addition to the annatto-related pinking discussed above, pinking can also occur in cheese made without any added color. In this case, pinking can be observed at various locations within a cheese block, but may present as a pink ring. The exact causes of this defect are still uncertain but this type of pinking is common in Italian-style cheeses, Swiss, Gouda and Cheddar. At this time, scientists believe that this type of pinking is likely the result of some chemical reactions facilitated by thermophilic bacteria such as Lactobacilli. These bacteria thrive at high temperatures and are generally added as a starter culture, adjunct or are present as the nonstarter microflora during ripening. 

Due to their ability to thrive at high temperatures, one theory is that this pinking defect is due to a Maillard-type reaction between certain free amino acids released during cheese ripening and reactive carbonyl compounds like diacetyl. Due to the illusive nature of this defect, science is still working on a solution. But screening starter cultures for specific Lactobacilli has allowed cheesemakers to avoid adding strains that are more susceptible to produce cheese with this pinking defect.

Avoiding browning 

Finally, browning is another color defect that can cause significant issues for cheesemakers. Browning can occur after baking of cheese, for example on pizza, or can develop in aged cheese.  Brown color development during aging is more likely to occur in cheese such as Gouda or Parmesan, and this browning is the result of a complex reaction between reducing sugars (such as galactose) and amino acids from the breakdown of the protein in cheese.

This defect is particularly common in cheeses that contain thermophilic cultures because these cultures often do not ferment the galactose fragment of the lactose molecule. This inability to ferment the galactose results in a buildup of this sugar, which coupled with warmer ripening temperatures, a lengthy storage and lower moisture contents, can result in Maillard browning. 

The best way to avoid this issue is to reduce the amount of these cultures used, store the cheese at slightly cooler temperatures or change the make procedure to reduce the amount of galactose present in the cheese. Brown color during aging can also occur in the absence of reducing sugars like galactose and instead involves reactions with carbonyl compounds like diacetyl.

While color defects can be frustrating, research has allowed us to uncover the science behind these defects and the best ways to prevent them. From improved packaging, to new retail displays to using DNA-based techniques to identity the specific bacteria responsible for defects, researchers and industry are working together to solve these issues. It’s an important partnership that must continue in order to preserve the premium image of cheese.