Questions & Answers
from "On Ice Cream" featured in Dairy Foods magazine
and sourced from "On Ice Cream" technical short courses.

Visual Defects - White Particles in Melted Ice Cream:

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

Answer: 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. 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.