Kitchen Pot Thickens, Drop by Drop

Many food formulations contain sugars and polysaccharides as thickeners that influence flow behavior, stability, processability, texture, and mouthfeel. Interfacial and rheological properties of key ingredients including polysaccharides influence production and processing of various foods, as well as the consumer perception and bioprocessing that begin withe every bite. Typically, chefs, formulators and regular cooks in kitchens judge stickiness, stringiness, spinnability, ropiness, and flowability by dripping a sauce or a mixture from a ladle, stretching a liquid bridge between finger and thumb, or by dispensing from a nozzle/bottle onto a substrate. Stream-wise velocity gradients associated with extensional flows spontaneously arise during these operations associated with dripping, dispensing or stretching liquid bridges. In spite of great advances in quantitative characterization of shear rheology response, elucidating, measuring and harnessing the extensional rheology, there remain well-known challenges associated with robust, reliable and affordable measurement of extensional rheology response. In this contribution, we present a range of experiments that emulate the kitchen flows and survey the influence of typical thickeners by quantitative studies relying on visualization and analysis of pinching flows encountered in dripping, dispensing, and stretched liquid bridges.