What causes pink discoloration in vanilla ice cream?

Bruce Tharp and Steve Young
Q What causes pink discoloration in vanilla ice cream?

A Discoloration in vanilla ice cream made using exempt, or so-called natural colors, can occur with changes in mix oxidation/reduction potential. Non-exempt artificial colors do not typically change color with minor changes in pH or acidity and that’s one of the benefits of artificial colors.

Annatto (an exempt color), which typically produces a desirable light to golden yellow color in vanilla ice cream, can range in hue from reddish/orange to yellow. If the oxidation/reduction potential of the mix changes due to composition and/or microbiological and chemical contamination, pink discoloration can result.

A frequent compositional cause of such discoloration is from use of certain whey ingredients. Whey can be sourced from different cheeses and processed differently, which impacts coloration with annatto. Interestingly, titratable acidity and pH do not seem to play major roles in ice cream discoloration due to whey. However, whey that is heat processed to improve water immobilization effects in the finished ice cream can cause pink discoloration. It is postulated that whey albumins, which coagulate with heat, indirectly change mix chemistry and are the cause. When low-temperature processed whey is used, pink discoloration does not occur. Typically, modern whey processing does not apply this excess type of heating. However, as more concentrated whey protein products are used and higher process temperatures applied, issues related to ice cream color could arise.

It is also important to be aware that whey from cheeses to which color has been added can also discolor ice cream in a different way. Oxidizing agent(s), which are used to bleach out color in the resulting whey, can be carried into the finished whey ingredient. Overuse or misuse of the oxidant also can directly or indirectly discolor the finished ice cream due to oxidation of a variety of mix components. This can result in faded, washed out, or in other ways, atypical coloration. It can also cause the development of oxidized flavor in ice cream.

Remember, whey ingredients are limited to 25% of total milk solids nonfat. If that restriction were to be removed, the quality, including the process history, of each individual whey ingredient becomes even more important to consider.

Q What causes the presence of white particles in melted ice cream?

A Such particles are either destabilized protein (the explanation behind the industry’s use of the term “curdy” to describe such a condition) or structures of agglomerated fat. The two types of particles can be distinguished from each other by the appearance of the melt. With destabilized protein (true “curdiness”), the particles are usually very small and are distributed throughout the mass of the melted product. On the other hand, fat agglomerate structures are larger and appear as flakes that float on the surface of the melt.

Protein destabilization occurs when the delicate equilibrium of protein stability, principally the balance of buffering salts and pH, is disturbed. Factors that can cause this disturbance include feed, stage of lactation and general health of the cow from which the milk is sourced; as well as treatment to the mix or its ingredients, including excessive shear and/or heat treatment, air incorporation, microbial acid production and psychotropic microorganism growth.

Sometimes protein destabilization is noticeable early on in the ice cream making process. At other times it does not become apparent until later. For example, extreme protein instability in mix can produce whey separation before freezing. This is particularly true in resale mix due to the extended storage time involved. However, an apparently homogeneous hard ice cream mix (or any of its dairy ingredients) may have been exposed to conditions that have not produced noticeable protein destabilization but have predisposed the protein to destabilization. Shear in the barrel of the freezer and freeze concentration then advance the destabilization process, thereby producing a curdy appearance or, in extremes, whey separation in the ice cream package.

Flaky particles often are produced when mix undergoes a high degree of shear in the freezer. High shear produces a semi-continuous fat matrix that contributes to mix structure. Frequently in some mixes, the level of fat agglomeration necessary to provide desirable handling, shape retention and/or eating qualities will consistently produce a flaky meltdown. However, the appearance of flakes in a sample of a product that usually shows a smooth melt reflects a departure from standard conditions that should be investigated. That investigation should include emulsifier type and level, homogenization, shear during mix transfer, agitation in the mix storage tank and variables in freezer operating conditions.