Why the Creamiest-Tasting Milk Isn’t Always the One You’d Expect

A carton of ultra-high-temperature, or UHT, milk looks deceptively simple: heat-treated, sealed, and shelf-stable for months without refrigeration. Yet behind the uniform white liquid lies a surprisingly tangled web of chemistry, physics, and human perception. A new study published in Food Science and Biotechnology has now mapped that web in unprecedented detail, showing that the quality of commercial UHT milk cannot be reduced to fat content or any single laboratory measurement. Instead, the research reveals that what consumers taste, see, and feel in their mouths emerges from an intricate interplay of particle structure, color, flow behavior, lubrication, aroma, and flavor cues that co-vary across real market products in ways no single instrument can capture.

The research team, led by Hee-Jin Kim and Hye-Seong Lee of Ewha Womans University in Seoul, took on a challenge that has long frustrated dairy scientists: commercial products differ not only in composition but also in raw material background, geographical origin, manufacturer, processing conditions, packaging, and storage history. Because these factors co-occur in real products rather than being independently manipulated in a laboratory, the team deliberately framed their work as an exploratory comparison of commercial product systems rather than a controlled experiment isolating the effect of any one ingredient. They selected eight market-available UHT milk products spanning skim, low-fat, and full-fat variants across three feeding-related product-system categories, identified as pasture-based/mixed-feeding, fermented-silage/mixed-feeding, and total mixed ration, or TMR, systems.

The analytical arsenal deployed was formidable. Physicochemical measurements captured basic composition with a MilkoScan FT2 instrument. Laser diffraction characterized the size distribution of fat droplets, which in milk, an oil-in-water emulsion, governs how light scatters and how the liquid flows. A spectrophotometer quantified color under standardized D65 illumination. A shear-rate-controlled rheometer measured apparent viscosity, and, in a particularly elegant touch, the same instrument was fitted with a ring-on-plate configuration lined with surgical tape to mimic the roughness of oral surfaces, allowing the researchers to measure friction coefficients at body temperature and generate Stribeck curves across boundary, mixed, and elastohydrodynamic lubrication regimes.

Complementing the physical measurements, electronic nose and electronic tongue systems generated instrumental fingerprints of aroma and taste variation. The electronic nose, equipped with fast gas chromatography columns, captured volatile profiles from the headspace of warmed samples, and a statistical screening procedure retained 24 peaks that were well represented by the major principal components. The electronic tongue, with its array of seven lipid-membrane and artificial-receptor sensors, distinguished the products with striking clarity: its first two principal components together explained nearly 94 percent of the variance in taste-related responses. The researchers were careful to note that these sensor systems do not directly measure human perception; they served as pattern-level evidence of product differentiation rather than as proxies for the tongue and nose of a drinker.

The human element came from two panels. Nine trained dairy panelists, each with more than three years of experience, rated the eight products on a battery of appearance, aroma, taste, flavor, mouthfeel, and aftertaste attributes using a nine-point intensity scale, following ISO 13299 guidelines with Williams Latin square presentation to balance order effects. Separately, 208 Korean adults aged 20 to 30, recruited at Ewha Womans University and screened for regular plain-milk consumption, rated overall liking on a nine-point hedonic scale under the same standardized room-temperature serving conditions, allowing direct alignment between expert perception and consumer preference.

The results painted a picture of coordinated, system-level differentiation. Within each product range, increasing fat content generally brought larger median particle diameters, greater lightness, higher apparent viscosity, lower friction in the mixed lubrication regime, and stronger perceived creaminess. Skim products had median droplet diameters around half a micrometer, while full-fat versions reached roughly 1.5 micrometers. Yet the pattern broke down in instructive ways. One full-fat product had a noticeably smaller particle size than its full-fat peers, and another showed lower friction despite comparable fat levels, evidence that lubrication behavior depends on particle-size distribution, interfacial composition, protein interactions, homogenization history, and heat treatment rather than fat alone. Color told a similar story: yellowness tracked the commercial product group more closely than fat level, with one product range appearing distinctly more yellow and another distinctly whiter.

Perhaps the most striking finding concerned creaminess itself. Among the three full-fat products, which differed significantly in particle size, viscosity, and friction, the trained panel detected no significant difference in perceived creaminess at all, with mean intensity scores clustering between 5.3 and 5.9. The authors interpret this as confirmation that creaminess is an integrated, emergent perception, one that the brain assembles from structural, rheological, tribological, and flavor cues rather than a direct readout of any single physical property. For product developers, this is a cautionary tale: engineering viscosity or droplet size in isolation may not deliver the mouthfeel consumers expect.

Consumer liking added another layer of nuance. The TMR full-fat product earned the highest liking score at 6.23, but a full-fat product from the pasture-based range remained among the least liked, scoring in the range of 3.59 to 4.14 for that product group. Fat content, in other words, did not uniformly buy favorability. A partial least squares regression model identified the sensory attributes driving preference: milky flavor, white color, and sweet taste were positively associated with liking, whereas hay-like flavor, yellow color, astringency, and salty taste pushed liking in the opposite direction. A follow-up model linking these liking-relevant sensory attributes to 34 instrumental predictors showed coordinated covariation across measurement domains, with whiteness and sweetness aligned with lightness, particle size, and viscosity, and hay-like, astringent, and salty notes oriented toward yellowness and selected electronic-sensor responses.

The statistical centerpiece of the study was a multiple factor analysis that integrated ten active data blocks comprising 59 variables, from sensory ratings and particle-size measures to color, rheology, tribology, and the electronic nose and tongue fingerprints. The first two dimensions of this integrated quality space accounted for over 82 percent of total variance and revealed two overlapping directions of differentiation: one a coordinated structural and mouthfeel axis linking droplet size, lightness, viscosity, creaminess, and oral coating, and a second flavor-appearance axis pitting hay-like, yellow, salty, and astringent notes against milky, white, and sweet ones. Because many variables loaded on both dimensions, the authors stress these represent overlapping system-level patterns, not independent causal pathways.

The team is candid about the limitations. Fat content, feeding system, origin, manufacturer, and processing history were confounded by design, so no single factor can be credited with the observed differences. Fatty acid analysis, which showed one pasture-range full-fat product with the highest omega-3 content and lowest omega-6 to omega-3 ratio, covered only the three full-fat products. The consumer panel was limited to younger Korean adults with an unequal sex distribution, and all samples were served at 24 degrees Celsius rather than refrigerator temperatures. Even so, the message for the dairy industry is clear and actionable: benchmarking and developing UHT milk demands integrated management of flavor, appearance, and oral-processing properties as a single quality system. In a global market where shelf-stable milk is a staple, the difference between a product consumers love and one they tolerate may hinge not on fat percentage printed on the label, but on the harmonious choreography of droplets, light, friction, and flavor reaching the mouth with every sip.

Subject of Research: Sensory, physical, and consumer-response quality differentiation of commercial ultra-high-temperature milk

Article Title: Integrated quality differentiation of commercial ultra-high-temperature milk: relationships among physical, sensory, and consumer-response characteristics

Article References: Integrated quality differentiation of commercial ultra-high-temperature milk: relationships among physical, sensory, and consumer-response characteristics. (n.d.). https://doi.org/10.1007/s10068-026-02311-9

Image Credits: AI Generated

DOI: 10.1007/s10068-026-02311-9

Keywords: UHT milk, sensory analysis, creaminess, tribology, rheology, consumer liking, electronic nose, electronic tongue, multiple factor analysis, dairy science, food emulsions, mouthfeel