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Study of the Physical Properties that Confer String Cheese with its Texture and Taste

Jungeun Kim, Keigo Nagao and Akihito Yamano

Summer 2020, Volume 36, No. 2 , 06-10

String cheese, which has a texture similar to that of jerky, the taste of fresh cheese, and strands that can be split apart, is a type of immature natural cheese. Natural cheese is generally prepared by adding lactic acid bacteria and rennet to milk, followed by adding salt to the coagulated milk protein to solidify it. String cheese is made from natural mozzarella cheese. After soaking the mozzarella cheese in hot water at 80°C, it can be stretched into a bar shape at room temperature and folded in half. This folding process is repeated to prepare the fibrous string cheese.

There is limited information about the history of string cheese. Some documents indicate that it was prepared in homes in Europe for a long time as a way of preserving fresh cheese, and/or it spread mainly as a menu item in pubs along the US coast. As a Japanese product, string cheese was developed by the Cheese Research Laboratory in Kobuchizawa in Yamanashi Prefecture in Japan, and string cheeses of various flavors are now on sale. According to an article by the Food Industry newspaper on July 27, 2019, annual domestic consumption of cheese is 350,000 tons, of which household consumption is 140,000 tons, and total cheese consumption is increasing every year. String cheese ranks high for its unique texture and strands, and its popularity has rapidly increased. However, there is a problem with insufficient milk supply due to an increase in the consumption of dairy products. For example, six pieces of string cheese, 1.5 cm in diameter and 10 cm in length each, require about 200 g of mozzarella cheese, which is prepared from 2 L of milk, corresponding to one-tenth of the daily production of a cow. The BBC News has criticized European laboratories for research into the efficacy of piercing a cow’s body to inject feed directly into its stomach to increase milk yield. Research and development on substitutes for string cheese are urgently needed.

Substitutional foods reproduce the texture, such as chewiness and softness, and the taste of original food. However, studying relevant parameters that reflect the characteristics of the original food is not simple because the texture and the taste of food generally depend on subjective factors such as individual differences in sense of taste and smell, changes in taste related to age, and amount of chewing and smelling. On the other hand, there are some objective factors that can be approached scientifically, such as internal structure, degree of crystallinity, crystal phase, and melting and crystallization process. X-ray measurement is one of the critical tools used to study these parameters. X-rays penetrate the material, are absorbed, and interact with the atoms and molecules that constitute the material to cause a diffraction phenomenon. Using the characteristics of X-rays, the internal structure at the micrometer (1 μm＝10⁻⁶ mm) to nanometer (1 nm＝10⁻⁹ mm) or Angstrom (1 Å＝10⁻¹⁰ mm) level can be visualized without destroying the material. The components of the material can be identified and quantified from the X-ray diffraction data. In addition to X-ray analyses, thermal analysis is also a powerful tool to study texture and taste. It allows the investigation of phase transition, melting, and crystallization temperature of materials, and so on.

In this study, we observed the internal structure of string cheese at the micrometer level and the periodic structure at the molecular level using X-ray analyses. The key features that were strongly related to the characteristics of texture and taste of string cheese are studied and the question of why string cheese splits is discussed in conjunction with an examination of the results of thermal analysis.

Highlights

  • X-ray CT, SAXS, and thermal analysis reveal how the microscopic and molecular structures of string cheese determine its characteristic texture, elasticity, and ability to separate into strands.
  • The fibrous structure consists of aligned aggregates of milk proteins rather than individual fibers, with water and melted milk fat creating weak interfaces that enable the cheese to split.
  • Small-angle X-ray scattering distinguishes structural contributions from milk fat crystals and milk proteins, showing that their relative crystallinity and abundance strongly influence texture and flavor perception.

Summary

Understanding food texture requires objective measurements of internal structure and phase behavior in addition to sensory evaluation. X-ray computed tomography (CT), small-angle X-ray scattering (SAXS), and thermal analysis provide complementary techniques for characterizing these structural features across multiple length scales without damaging the sample. Although these methods are more commonly associated with materials science, they can also reveal how food microstructure influences physical properties.

Three-dimensional X-ray CT imaging shows that string cheese contains vertically aligned networks of aggregated milk proteins interspersed with irregular distributions of water, oil, and salt. Rather than forming continuous individual fibers, the protein network consists of bundled structures approximately 1–11 μm thick. This organization explains the characteristic fibrous appearance while providing insight into the material's mechanical behavior.

Thermal analysis demonstrates that water begins evaporating at relatively low temperatures while milk fat melts between approximately 28°C and 38°C. Heating promotes separation of water and fat, creating weak interfaces between protein aggregates. During manufacture, stretching and folding at elevated temperature allow melted fat and water to redistribute between aligned protein structures. Upon cooling, these interfaces remain as preferred fracture paths, allowing the cheese to separate cleanly into strands.

SAXS measurements further distinguish molecular-scale structural changes. A periodic spacing of about 4 nm is associated with crystalline milk fat, while a second periodic feature near 16 nm is attributed to structural organization within the milk protein network. Heating and cooling alter the crystalline state of the milk fat while leaving the protein periodic structure largely intact. Comparison of cheeses with different sensory characteristics indicates that elasticity and flavor are closely related to both the quantity and crystallinity of milk protein and milk fat structures. These findings demonstrate how advanced X-ray characterization techniques can quantitatively relate microscopic structure to macroscopic food properties, providing valuable tools for developing alternative dairy products and other engineered foods.

Frequently asked questions

X-ray imaging methods such as computed tomography allow researchers to visualize the internal three-dimensional structure of food without cutting, staining, or otherwise altering the sample. This preserves the natural arrangement of proteins, fats, and water while providing detailed information about microstructure. Small-angle X-ray scattering extends this analysis to the nanometer scale by revealing periodic molecular structures that influence texture and mechanical behavior.

The characteristic stringing behavior results from the combination of aligned milk protein aggregates and thin interfaces containing water and melted milk fat. During production, stretching and folding orient the protein network while redistributing fat and water between protein bundles. These interfaces have lower cohesive strength than the protein aggregates themselves, allowing the cheese to split cleanly along predetermined paths.

Milk fat contributes to both softness and mouthfeel. Thermal analysis shows that different milk fat components melt between approximately 28°C and 38°C, close to body temperature, producing the smooth texture experienced during eating. The crystallization behavior of the fat during cooling also influences elasticity and overall texture.

SAXS measures periodic molecular structures that cannot be observed with conventional imaging. In cheese, it identifies periodic features associated with crystalline milk fat and organized milk protein structures. Monitoring how these features change during heating and cooling helps explain the relationship between molecular organization and macroscopic properties such as elasticity and texture.

Comparisons between cheeses with different sensory characteristics show that elastic cheeses generally contain a higher contribution from ordered milk protein structures, while cheeses with milder texture may contain greater amounts of less crystalline milk fat. The balance between protein organization and fat crystallinity directly affects firmness, elasticity, and mouthfeel.

Thermal analysis measures phase transitions such as melting, crystallization, and water evaporation. These transitions strongly influence texture, processing behavior, and eating quality. By identifying the temperatures at which these events occur, manufacturers can better optimize production processes and control product consistency.

Quantitative structural measurements make it possible to identify the physical features responsible for desirable textures instead of relying solely on sensory testing. This information can guide the development of plant-based, low-fat, casein-free, gluten-free, or functional foods by helping developers reproduce the structural characteristics responsible for the texture and eating experience of conventional products.

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