"On Ice Cream" featured in Dairy Foods magazine
and sourced from "On Ice Cream" technical short courses.
Defects - White Particles in Melted Ice Cream:
What causes the presence of white particles in melted ice cream?
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
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
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.
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