The yeast Pichia anomala inhibits the spoilage mold Penicillium roqueforti in laboratory experiments with high-moisture wheat in malfunctioning airtight storage. The ability of P. anomala to prevent mold growth during 14 months of grain storage was evaluated in outdoor silos with different air permeabilities. Freshly harvested wheat in 160-kg portions was inoculated with 102 colony-forming units (cfu) g-1 P. roqueforti, alone or together with 104 cfu g-1 P. anomala. During the first month P. anomala increased to about 106 cfu g-1 in the treated silos to reach 107 cfu g-1 after 9 months. Naturally occurring P. anomala in the untreated silos increased from 102 to about 103 cfu g-1 during the first month and reached the same level as the treated silos after 9 months. Oxygen levels were reduced below the detection limit within 1 day, while carbon dioxide levels increased to 80-90% during the first month. P. roqueforti did not grow in wheat treated with P. anomala, regardless of silo permeability, but had increased to 105 cfu g-1 in the untreated silos after 14 months of storage. © 2002 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.