<p>Andean grains and cereals such as quinoa (<i>Chenopodium quinoa</i> Willd.), kañiwa (<i>Chenopodium pallidicaule</i> Aellen), and amaranth (<i>Amaranthus caudatus</i>) are emerging as strategic ingredients in the formulation of innovative foods owing to their high nutritional value, absence of gluten, and richness of bioactive compounds. This scientific review provides an in-depth analysis of the physical and technological mechanisms involved in thermal expansion (puffing and popping), including traditional (direct fire and sand bed), conventional (puffing gun), and emerging (microwave and infrared) methods. Critical factors affecting puffing efficiency (moisture content, temperature, pressure, and grain structure) and their impact on physicochemical properties, such as starch gelatinization, protein digestibility, and preservation of functional compounds, are discussed. Furthermore, the potential of expanded grains for food customization through 3D printing was explored, highlighting their favorable rheological behavior and formulation capacity. Finally, industrial opportunities and technical challenges that pave the way for functional and sustainable food innovation adapted to different population groups are identified.</p>