Pseudocereals are gluten-free, nutrient-dense raw materials that are being considered for the production of gluten-free products, especially bread. This study proposes a gluten-free sourdough formula based on equal amounts of amaranth, buckwheat, and quinoa with a dough yield of 250, and an elaboration method to obtain ripe sourdough. Sourdough was characterized in terms of microbiology, pH, and total titratable acidity. The established protocol made it possible to obtain a spontaneous ripe sourdough with lactic acid bacteria populations of 9.60 ± 0.02 log CFU/g and total yeasts and non- yeast populations (lysine positive) of 7.91 ± 0.15 and 7.52 ± 0.10 log CFU/g, respectively. Great pH stability and total titratable acidity were maintained in the ripe sourdough phase, with values of 4.04 ± 0.02 and 18.39 ± 0.56 ml NaOH 0.1 M/10 g, respectively, at the time of the next refreshment. The use of this sourdough could be an interesting alternative for the production of not only gluten-free bread but also other gluten-free products.