A minor story of interest to food technologists grabbed headlines briefly this summer. This event was widely reported, and one example can be found here: “Walmart-brand ice cream sandwich won’t melt in 80-degree heat” from the Washington Post (http://www.washingtonpost.com/blogs/capital-weather-gang/Wp/2014/07/31/video-walmart-brand-ice-cream-sandwich-wont-melt-in-80-degree-heat/). The reports led to an admirable number of everyday science experiments; many of which were captured on YouTube. (Search for keywords: melt, ice cream, and sandwich.)
It’s too bad that Maya Warren and Richard Hartel’s paper, “Structural, Compositional, and Sensorial Properties of United States Commercial Ice Cream Products,” published in this month’s journal was unavailable at the time. Warren and Hartel study a wide range of commercial ice cream products in the U.S. detailing how compositional and microstructural aspects of ice cream affect the behavior of ice cream products, as well as sensory properties. Having read the paper, I think the mystery of the melting ice cream can be found in its ingredients. A combination of gums, calcium sulfate, and, I would guess, the percentages of moisture and fat translate into this product being easier to make into a “sandwich” as well as decreasing its melting rate. The next time questions about frozen dairy novelties come up, we know where to turn for answers. As Warren and Hartel point out, there is a wide range of commercially-available ice cream products with different formulations, including novelty items such as ice cream sandwiches. We can expect an equally wide range of sensory characteristics such as melt rates in these products.
According to Warren and Hartel, ice cream is a complex, partially frozen food composed of partially-crystalline individual fat globules, partially-coalesced fat globules (partially crystalline), ice crystals, and air cells, all dispersed in an unfrozen fluid phase. In this complex mixture, microstructural components (fat globules, ice, and air) are critical to the overall structure and properties and differ greatly depending on the formulation and the processing conditions used to make ice cream. These microstructural components also affect meltdown/drip-through behavior and sensory properties. The researchers analyzed commercial vanilla ice cream products from the United States (full fat, low-fat, and nonfat) for their structural, behavioral (i.e., melt rate and drip-through), compositional, and sensory attributes. To determine relationships and interactions, principle component analysis and multivariate pairwise correlation were performed within and between the instrumental and sensorial data. They found that greasiness and creaminess negatively correlated with drip-through rate, and creaminess correlated with percent total fat and percent fat destabilization. Percent fat did not determine the melt rate on a sensory level. However, drip-through rate at ambient temperatures was predicted by total fat content of the samples. Based on sensory analysis, high-fat products were noted to be creamier than low and nonfat products. Iciness did not correlate with mean ice crystal size and drip-through rate did not predict sensory melt rate. The researchers also found that greasiness was positively correlated with total percent fat destabilization and mean air cell size was positively correlated with denseness. Commercial ice cream products in the U.S. vary widely in composition, structure, behavior, and sensory properties.