Category: MTM

Merlot and Mistletoe: A Tribological Test of Holiday Drinks

As we’re in the holiday period here at PCS Instruments, we thought it would be fun to investigate the tribological properties of a few of the different drinks options on offer this winter season. This falls under the umbrella of oral tribology and focuses on how food and drinks feel as you consume them.

There are many examples of the MTM being used to test and evaluate the properties of foods and drinks, including work to investigate the mouthfeel of wines, the creaminess of chocolates, and the richness of mayonnaise!

With the global food and beverage market size being valued at $7,221.73 billion in 2023, it’s easy to see why academia and industry are using the MTM to gain every advantage possible.

The drinks we chose for our investigation were:

  • Mulled Wine
  • Advocaat
  • Hot Chocolate
  • Irish Cream
  • Port

These were chosen to give us a range of different mouthfeels to investigate and compare. Irish cream and advocaat both have a distinct and classic creamy richness, port and mulled wine have a more dry and crisp feel, while hot chocolate brings in a whole new complex factor of suspended particles.

To test the drinks, we created a bespoke profile for the MTM that consisted of multiple Stribeck steps. The instrument was set up with the pot filler fitted and using PDMS specimens.

The aim of our investigation was to see if we could differentiate not only between the drinks with very diverse mouthfeels, but also between the ones that have similar properties and ingredients; the mulled wine and port, and the Irish cream and advocaat.

We succeeded in this aim as you can see below! The results below broadly align with what we would expect. The mulled wine and port can be grouped together, the advocaat and Irish cream together, and the hot chocolate behaving slightly differently to them all.

We aren’t going to analyse the results too closely in this investigation; we will leave that for you to do as you sit down for a drink over the festive period. However, there are a couple of interesting points to pull out for you to ponder during these long winter nights.

First, comparing port to mulled wine. If you happen to have a sip of these drinks, see whether you pick up on the subtle difference in mouthfeel (not just flavour) between them. When we tried both, we noticed that the port had a richer, heavier feel to it; and that it seemed to be slightly higher in viscosity.

This could explain the lower initial friction coefficient and the earlier move into the mixed and EHD regimes on the Stribeck curve, which would be consistent with findings on the effect of viscosity.

Second, comparing hot chocolate to the other drink options. As you can see below, hot chocolate behaves quite differently to both the thick and rich Irish cream, and the thin, crisper mulled wine. There are many possible explanations for this behaviour.

One possible reason for this is the makeup of the hot chocolate. The protein-filled milk would explain the low boundary friction, and the suspended particles of chocolate powder being entrained into the contacting PDMS surfaces, increasing their surface roughness and postponing the transition to the boundary and EHD regimes.

We hope you will try all three at some point over the holidays to develop your own hypotheses and please do let us know! We would love to read your thoughts on it!

Finally, we’ll have a look at two drinks with very different mouthfeels: mulled wine and Irish cream. With such different viscosities and ingredients, it’s easy to see why these would be so easy to compare and contrast. The thicker Irish cream shows consistently better lubricating properties across all the lubrication regimes as well as an earlier transition between them.

So, what do we recommend? Simply put, our recommendation is to drink whatever brings you joy this holiday season, we won’t draw any conclusions about what drinks are best or worst! 

If you work in the field of biotribology or think it might be relevant to your work – whatever the area of specialisation – please do get in touch with us here so we can talk through your needs and help you expand your ability to test, analyse and compare the formulations you work with.

Keep an eye out for another set of upcoming Christmas-themed tests with our Christmas Condiment King Competition!

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