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The flavor and aroma development in fermented foods is intricately tied to the mixing dynamics during fermentation. This review explores how variations in mixing influence the physical, chemical, and microbial interactions within fermentation systems, ultimately affecting sensory characteristics such as flavor and aroma. Factors, such as rheology, shear forces, and fluid flow patterns, are critical in mass transfer, microbial activity, and the release of volatile compounds, contributing to fermented products' sensory profile. Examples from common fermented foods—including bread, yogurt, beer, wine, and cheese—highlight how controlled mixing can optimize the release of desirable flavor compounds, improve biosynthesis yields, and reduce technological complexity. Understanding these physical interactions is essential for advancing fermentation processes in the food industry, leading to a higher product quality, a better flavor retention, and an enhanced consumer satisfaction.

Innovations in fluid mechanics have been leading to better food since ancient history, while creativity in cooking has inspired fundamental breakthroughs in science. This review addresses how recent advances in hydrodynamics are changing food science and the culinary arts and, reciprocally, how the surprising phenomena that arise in the kitchen are leading to new discoveries across the disciplines, including molecular gastronomy, rheology, soft matter, biophysics, medicine, and nanotechnology. This review is structured like a menu, where each course highlights different aspects of culinary fluid mechanics. Our main themes include multiphase flows, complex fluids, thermal convection, hydrodynamic instabilities, viscous flows, granular matter, porous media, percolation, chaotic advection, interfacial phenomena, and turbulence. For every topic, an introduction and its connections to food are provided, followed by a discussion of how science could be made more accessible and inclusive. The state-of-the-art knowledge is then assessed, the open problems, along with the likely directions for future research and indeed future dishes. New ideas in science and gastronomy are growing rapidly side by side.

This paper investigates the self-cleansing performance of an airlift pump with a u-bend. For this purpose, an experimental test model is used to assess the effect of air supply on the pump's ability to lift water and remove particles under different submergence ratios and particle concentrations. In addition, a simple yet accurate fluid mechanical model is used to rationalize the experiments with individual particles, and to predict the critical water velocity required for removal from the pipe bend. Our experimental results show that the airlift pump is self-cleansing for particle concentrations corresponding to as much as 70% of the cross-sectional area in the u-bend. Furthermore, the self-cleansing ability is relatively independent of the submergence ratio and almost entirely determined by the shear stress. However, the submergence ratio strongly affects energy use, and we find that submergence ratios around 0.75 provide a good compromise between energy use and particle removal efficiency.

“A basic and basically unsolved problem in fluid dynamics is to determine the evolution of rising bubbles and falling drops of one miscible liquid in another” [D. D. Joseph and Y. Y. Renardy, Fundamentals of Two-Fluid Dynamics: Part II: Lubricated Transport, Drops and Miscible Liquids (Springer Science & Business Media, 2013), Vol. 4.]. Here, we address this important literature gap and present the first theory predicting the velocity, volume, and composition of such drops at low Reynolds numbers. For the case where the diffusion out of the drop is negligible, we obtain a universal scaling law. For the more general case where diffusion occurs into and out of the drop, the full dynamics is governed by a parameter-free first-order ordinary differential equation, whose closed form solution exists and only depends on the initial condition. Our analysis depends primarily on “drop-scale” effective parameters for the diffusivity through the interfacial boundary layer. We validate our results against experimental data for water drops suspended in syrup, corresponding to certain regimes of the mass exchange ratio between water and syrup, and by this explicitly identify the drop-scale parameters of the theory.

In this Special Issue, we celebrate the connection between the physics of fluids, food science and education. We received over 30 articles concerning all types of kitchen flows, from simple to complex, from small to large scale. They include research articles, short reviews, educational articles, methods papers and expert tutorials. In the remainder of this editorial, we will summarise these works and highlight some exciting new opportunities in this effervescently growing branch of science.

Our work focuses on an experimental investigation of droplets freely rising through a miscible, more viscous liquid. We report observations of water droplets rising through glycerol and corn syrup, which are common household ingredients. Immediately after the drops are formed, they take on prolate shapes and rise with constant velocity without expanding in size. However, after a critical time predicted by our scaling arguments, the drops continually grow into oblate spheroids, and as they mix with the ambient liquid, their volume increases and their velocity decreases, eventually following power laws. We present scaling relations that explain the main observed phenomena. However, the power laws governing the rate of the volumetric increase and the velocity decrease, namely, t1=2 and t􏰑1=2, respectively, remain points of further investigation.

An inherent problem with microfluidic filters is the tendency to clog, especially when applied to cells due to their geometrical complexity, deformability, and tendency to adhere to surfaces. In this work, we handle live algal cells of high complexity without signs of clogging, achieved by exploiting hydrodynamic interactions around trilobite-shaped filtration units. To characterize the influence of cell complexity on the separation and concentration mechanisms, we compare the hydrodynamic interactions to those of synthetic, rigid microparticles. We discover that simple rolling along the filter structures, which prevents clogging for particles, cannot be applied to cells. Instead, we find that inertial effects must be employed to minimize the filter interactions and that this modification leads to only a minor reduction in device performance.

We present a detailed experimental study of a hydrodynamic filtration microchip and show how chip performance can be tuned and clogging avoided by adjusting the flow rates. We demonstrate concentration and separation of microspheres at throughputs as high as 29  ml/min and with 96% pureness. Results of streakline visualizations show that the thickness of a tunable filtration layer dictates the cutoff size and that two different concentration mechanisms exist. Particles larger than pores are concentrated by low-velocity rolling over the filtration pillars, while particles smaller than pores are concentrated by lateral drift across the filtration layer. Results of microscopic particle image velocimetry and particle-tracking velocimetry show that the degree of lateral migration can be quantified by the slip velocity between the particle and the surrounding fluid. Finally, by utilizing differences in inertia and separation mode, we demonstrate size-based separation of particles in a mixture

By the use of an experimental setup for microfluidic flows, we have characterized the separation and concentration characteristics of the so-called Trilobite™ separation unit. Our separation unit consists of microfluidic channels and an elliptical separation geometry with a solid and a permeable wall region. We show that it is possible to adjust the thickness of different flow layers by changing the flow rates and pressure drop over the permeable wall. For high pressure drops, the separator shows promising concentration characteristics. For low pressure drops, an increase in flow rate results in a thinning of the flow layers. For sufficiently high flow rates, it should therefore be possible to create flow layers sufficiently thin that the particle separation is entirely dominated by hydrodynamic forces. This, in turn, will enable clog-free particle separation.

Innovations in fluid mechanics have been leading to better food since ancient history, while creativity in cooking has inspired fundamental breakthroughs in science. This review addresses how recent advances in hydrodynamics are changing food science and the culinary arts and, reciprocally, how the surprising phenomena that arise in the kitchen are leading to new discoveries across the disciplines, including molecular gastronomy, rheology, soft matter, biophysics, medicine, and nanotechnology. This review is structured like a menu, where each course highlights different aspects of culinary fluid mechanics. Our main themes include multiphase flows, complex fluids, thermal convection, hydrodynamic instabilities, viscous flows, granular matter, porous media, percolation, chaotic advection, interfacial phenomena, and turbulence. For every topic, an introduction and its connections to food are provided, followed by a discussion of how science could be made more accessible and inclusive. The state-of-the-art knowledge is then assessed, the open problems, along with the likely directions for future research and indeed future dishes. New ideas in science and gastronomy are growing rapidly side by side.

Fysikk handler ikke bare om det største og det minste. Det er mye spennende fysikk på mer dagligdagse størrelsesskalaer også, for eksempel, på kjøkkenet. Der er det mye som renner – kaffe, champagne, pannekakerøre og oppvaskvann. Væsker beskrives av et sett av matematiske ligninger kalt Navier-Stokes ligningene. De ser ganske uskyldige ut, men har mange overraskelser å by på. Dagens gjest er fluidmekaniker og forsker ved Universitetet i ̽����ѡ og bruker eksempler fra kjøkkenet for å formidle fagfeltet. Podcasten ble spilt inn 13. februar 2023 og varer 1 time og 27 minutter.

A hydrodynamic micro particle separator has been tested by means of streakline visualizations and Particle Image Velocimetry (PIV) for different flow configurations. By adjusting the pressure drop and the Reynolds number, it is possible to determine the thickness of a flow layer that ends up as permeate. The results of the streakline visualizations show that the permeate flow thickness decreases with decreasing pressure drop between the inlet and the permeate outlet. Increasing the Reynolds number has the same effect. A phase averaged PIV method was used to extract the velocity fields from the image data. By visual inspection of the velocity vector plots, it was found that the location of the stagnation points on the separator pillars depend on the Reynolds number.