Development of the yeast flora of whole-crop maize during ensiling and during subsequent aerobiosis

The fresh maize plant was inhabited by non-fermenting basidiomycetous yeast species, viz. Candida ingeniosa, Cryptococcus laurentii, Sporobolomyces roseus, Sporidiobolus salmonicolor and Rhodotorula rubra. These species had vanished after 2 days of anaerobiosis in a laboratory-scale silo. After this time, ascomycetous species tolerant to acetic acid were isolated. Successively Candida holmii, C. milleri, C. krusei, C. lambica, C. famata, Geotrichum candidum and Hansenula anomala were encountered. Except for C. famata and G. candidum these yeasts vigorously ferment glucose. Total yeast counts were 10⁷ g^?1 during the first 2 weeks and gradually decreased to about 10⁵ g^?1 after 4 months. This shows that anaerobic silage provides an adverse environment for yeasts. Exposure of maize silage to air resulted in complete consumption of lactic and acetic acids within 5 days. This was due to growth of C. hoimii, C. lambica and C. milled. The physiologically similar yeast species C. holmii and C. milled were both abundant from the early stage of the fermentation and during aerobiosis. However, C. milled predominated in the first 2 weeks of anaerobiosis. The less frequently occurring yeast species C. famata, G. candidum and H. anomala assimilated lactic acid and ethanol as well as minor products of bacterial sugar fermentation such as acetoin and butan-2,3-diol but not diacetyl.