Question

Based on material science and diffusion, how is beef marinated? This question was given by my professor as a way to apply diffusion to the real world and if you can give me a basic understanding that would be awesome. Thank you.

Answer 1

DIFFUSION plays an essential role in our daily lives. It can be observed in a splash of perfume gradually scenting a room or a drop of ink bleeding onto a page. Thermal diffusivity is essential in the transfer of heat from the stovetop to a pan. To describe how the spontaneous movement of solute particles is driven by a concentration gradient, Fick’s first law of diffusion provides a physical explanation, as follows:

J = D * (dC/dx)

In this one-dimensional simplification of Fick’s first law, J is the solute flux, expressed as net moles of molecules flowing through a cross-sectional area per unit time perpendicular to the x-axis (in mol/m2s); D is the diffusion coefficient (in m2/s); dC is the difference in solute concentration (in mol/m3); and dx is the characteristic length scale of the system (in m). This simple formulation of Fick’s first law can describe numerous complex phenomena in the context of food and cooking: plant growth and ripening is triggered by the diffusion of small molecules such as ethylene, brining and marinating rely on the diffusion of salt and sugar molecules into meat, and dehydration occurs due to the diffusion and evaporation of water molecules from a food. Even the changing moisture profiles across a spaghetti noodle as it hydrates during cooking can be predicted using Fick’s first law.

To reduce cooking time, a more recent recipe suggests to “chop small to chop time”; We use Fick’s first law to explain why this small dicing method works: by increasing the area of the vegetable-water interface, a greater number of molecules can diffuse into the stock per unit time; the larger interface and smaller dice effectively increases dC/dx. Consequently, J increases, which means that the stock achieves the same level of flavor within a shorter period of time.