The microbiological make up of redried tobacco is almost exclusively made of bacteria from gram positive bacillus family with the exception of a small number of moulds characteristic of storage room flora. This is not surprising since bacillus can form spores that are fairly resistant to heat treatment normally applied during tobacco processing. On tobacco most of the bacillus cells are present in a dormant spore form. They are inactive as long as temperature and humidity remain relatively constant-anormal situation found under standard storage conditions. A correlation between tobacco dryer conditions and cigarette off-taste caused by microbial activation was established. Germination of dormant bacillus spores and the subsequent release of dipicolinic acid are involved in the mechanism resulting in the off-taste. It has been shown that the amino-acid L-alanine naturally present in tobacco plays a predominant role in the germination process. L-alanine binds to a ger mination site at the surface of the spore thus causing activation. A competitive inhibitor for the initiation of germination by L-alanine is D-alanine. The binding affinity of D-alanine to the germination site is stronger than that of the germination site is stronger than that of L-alanine so it is able to block initiation of germination. D-alanine was evaluated specifically as a control mechanism for the Bacillus spore population of tobacco. The efficacy of D-alanine was quantified in synthetic media against pure Bacillus pumilus spores, the predominant strain on tobacco and evaluated in tobacco extract and tobacco cut-filler by measuring germination yields under conditions favoring activation. Minimum germination inhibitory concentration was found around 200 ppm. Conditions favoring germination were simulated in semi-industrial trials with and without D-alanine added. A subjective off-taste was detected on cigarettes prepared with untreated tobacco, while the version treated with 0.5 gram D- alanine per kilo tobacco was subjectively in line with a standard control.