Chestnuts roasting on an open fire,

Jack Frost nipping at your nose,

Yuletide carols being sung by a choir

And folks dressed up like Eskimos…

Irish cream liqueur in a glass with cinnamon on wooden background

Christmas is one of my favorite times of the year. However, having braved the cold to sing carols and eat roasted chestnuts, my favorite way to wind down, and increase the calorie count for the day, is to reach for the Irish cream liqueur when I get home. And as I snuggle up on the sofa like an oversized cat, supping my liqueur while warming myself in the glow of a fire and watching TV re-runs of classic 1980’s films (Star Wars appears to be the favorite this year), my mind is never far from the fact that particle size analysis has had a hand in ensuring that the drink in my hand is luxuriously creamy rather than tasting like a glass of fat.

Back when I was a boy, cream liqueurs, such as the one you are imagining me drinking now, had a short shelf life. Although this offered my parents an excuse to complete an entire bottle within the 12 days of Christmas, it did not help with the marketing of the product. One of the reasons for the poor shelf life related to particle size and the affect this has on emulsion stability. Overtime, the milk fat particles within the drink would gather at the top of the bottle (creaming) and would then flocculate and eventually coalescence. If the drink was consumed quickly, shaking the bottle would re-disperse the particles. However, if it was left for too long a layer of fat would slowly form, which my parents claimed was not quite as palatable!

The solution to this issue related to particle size. Researchers studied the particle size of cream liqueurs using laser diffraction and determined that homogenization to a finer particle size would improve the stability of the milk fat emulsion. In addition, they were able to understand the role milk proteins have in either stabilizing the emulsion or causing destabilization through bridging flocculation. The result was the development of a formulation which remained stable for many months, ultimately leading to an increase in sobriety in the Kippax household at Christmas time!

So, if you, like me, are partial to a glass of cream liqueur, either to relax following a busy Christmas day or to toast in the New Year, spare a thought for the particle scientists who made it possible. Thanks to them, you can definitely feel like the cat that’s got the cream.


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