Cheese fondue is a popular Swiss dish prepared by melting cheese under the addition of wine, starch, and seasoning. The flow behavior or rheology of fondue is crucial for mouthfeel, flavor release, and the tendency of fondue to cling to the bread. Fondue is a complex multiphase system whose rheology is determined by the interactions of its colloidal ingredients. We establish cheese fondue as a water-continuous system with dispersed fat droplets, charged caseins, and starch granules. Irreversible phase separation, a common issue in fondue preparation, may be prevented by addition of a critical minimum starch concentration. Fondue was found to be a shear-thinning yield stress fluid, which is desirable for mouthfeel and facilitates fondue to cling to the bread for consumption. Fondue showed a viscoelastic stress response around the gel point (G′ ≈ G″), which is proposed as crucial for the balance of orally perceived gumminess (G′) and liquidity (G″). Ethanol addition and lowering pH toward the isoelectric point of casein, as associated with wine addition, decrease fondue viscosity due to a decrease in casein micelle size. Below the isoelectric point of casein, fondue is unstable and phase separates, potentially impeding fondue digestion. Thus, fondue rheology is governed by the complex colloidal interactions within its ingredients, and ultimately determines fondue eating experience.
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