Foaming performance of plant-based milks for barista application: from formulation and processing history to interfacial structure, foam formation and stability

Background Plant-based milks are increasingly consumed as dairy alternatives, yet achieving consistent, barista-grade foaming performance remains challenging. Foamability and foam stability arise from tightly coupled bulk and interfacial processes, including air incorporation, adsorption and rearrangement of surface-active species, and subsequent changes in bubble size distribution driven by drainage, coarsening, and film rupture. Compared with bovine milk, plant-based milks exhibit wider variability in protein composition and structural state, and often contain endogenous lipids and insoluble particles that can impair foam stability. Scope and approach This review synthesises current understanding of foaming in plant-based milks from an interfacial perspective, linking formulation variables (protein type and state, lipids, particles, polysaccharides, and emulsifiers) with processing history (heat treatment, homogenisation, and emerging non-thermal technologies) that reshapes bulk microstructure and interfacial viscoelasticity. We critically assess common characterisation approaches, highlighting the strengths and limitations of standard foaming tests and the value of complementary measurements (e.g., microstructural imaging and interfacial rheology) under application-relevant conditions. Key findings and conclusions Foam performance is mainly governed by interfacial competitive adsorption, primarily between proteins and small molecule emulsifiers, and by matrix effects from surface-active and antifoaming species. Rapidly adsorbing surfactants may enhance initial foam formation yet can displace proteins and weaken interfacial films; endogenous lipids and oil droplets can accelerate collapse via entry, bridging, and film rupture; and processing-driven protein modification often shows a balance point, where moderate denaturation can enhance the protein unfolding and interfacial rearrangement, whereas excessive aggregation can reduce interfacial mobility. This review highlights the critical need for coffee-relevant protocols that use physicochemical and interfacial properties to predict foaming outcomes.