<p>Brewer’s surplus yeast is the second-largest by-product of the brewing industry. Despite its rich nutrient profile, including protein, amino acids, B vitamins, oligosaccharides, and minerals, most of it is discarded. This study aims to valorize the surplus yeast of <i>Saccharomyces cerevisiae</i> DSM 2155 generated at a local Madeiran enterprise. The surplus yeast was used to remove monosaccharides remaining as secondary products from the synthesis of galacto-oligosaccharides via fermentation and for producing yeast extract serving as a nitrogen source for the growth of Gram-negative (<i>Escherichia coli</i>) and Gram-positive (<i>Staphylococcus aureus</i>, lactobacilli) microorganisms. Two commercial β-galactosidases, Enzeco Fungal Lactase Concentrate (Enzyme Development Corporation, USA) and Biolactase F Conc (Biocon, Spain), were immobilized in glutaraldehyde-activated halloysite nanotubes and used in a repeated batch operation for the synthesis of galacto-oligosaccharides from lactose. After two rounds of synthesis, both synthesis products roughly consisted of 36% galacto-oligosaccharides, 44–49% lactose, 15–20% monosaccharides (glucose and galactose). Fermentation with surplus yeast led to a composition of 41% galacto-oligosaccharides, 47–51% lactose, and 8–12% monosaccharides, due to an almost complete removal of glucose, decreasing its content to only 1% in the final preparations. In a parallel assay, yeast extract was produced by autoclaving, autolysis, and enzymolysis using Viscozyme L (Novozymes, ND) and used as culture medium for <i>E. coli</i>, <i>S. aureus</i>, and <i>Lactiplantibacillus plantarum</i>. This study demonstrates a dual strategy for valorizing brewer’s surplus yeast, yielding nutritionally valuable resources for potential biotechnological applications.</p>