Control of contaminant microorganisms in fermentation processes with peroxygen-releasing compounds

1. A method for controlling growth of contaminant microorganisms in a fermentation process comprising adding a nitrogen-free peroxygen-releasing compound to one or more steps of a fermentation process, wherein the fermentation process comprises (i) providing a fermentation vessel; (ii) providing an inoculant, a fermentable sugar and process water; (iii) introducing separately, or in any combination, the inoculant, fermentable sugar and process water into a fermentation vessel to provide a fermentation broth; and (iv) contacting the inoculant with the fermentable sugar in the fermentation vessel at a temperature at which the inoculant converts the fermentable sugar to ethanol.

2. The method of claim 1 further comprising adding nutrients to one or more of the inoculant, fermentable sugar and process water or directly to the fermentation vessel.

3. The method of claim 2 wherein the peroxygen-releasing compound is added to the inoculant, fermentable sugar or process water prior to introducing the inoculant, fermentable sugar or process water into the fermentation vessel.

4. The method of claim 1 wherein the inoculant is a yeast inoculum produced by contacting a yeast starter culture and a nutrient composition in a propagation tank.

5. The method of claim 4 wherein the fermentation process is a batch fermentation, and the peroxygen-releasing compound is added to the fermentation vessel prior to adding the fermentable sugar to the fermentation vessel.

6. The method of claim 4 wherein the fermentation process is a continuous fermentation process and the peroxygen-releasing compound is added in the yeast propagation step to produce the yeast inoculum or during the contacting step (iv).

7. The method of claim 2 wherein the fermentable sugar is derived from corn using a dry grind process.

8. The method of claim 2 wherein the fermentable sugar is derived from corn using a wet mill process.

9. The method of claim 2 wherein the fermentable sugar is sugarcane- or sugar beet- or molasses-based fermentable sugar.

10. The method of claim 2 wherein the peroxygen-releasing compound is an alkali metal, alkaline earth metal or transition metal compound of a percarbonate, perborate or peroxide, or a mixture of two or more thereof, provided the compounds in the mixture are compatible.

11. The method of claim 10 wherein the peroxygen-releasing compound is selected from the group consisting of sodium percarbonate, sodium perborate, sodium peroxide, calcium peroxide, magnesium peroxide and zinc peroxide.

12. The method of claim 11 wherein the peroxygen-releasing compound is sodium percarbonate or sodium perborate.

13. The method of claim 12 wherein the peroxygen-releasing compound is used in hydrate form.

14. The method of claim 1 wherein the peroxygen-releasing compound is added in an amount to provide a concentration of the peroxygen-releasing compound of 0.0001% to 5%, based on the total weight of the fermentation broth.

15. The method of claim 14 wherein the peroxygen-releasing compound is added in an amount to provide a concentration of the peroxygen-releasing compound of 0.0005% to 1%, based on the total weight of the fermentation broth.

16. The method of claim 14 wherein the peroxygen-releasing compound is added in an amount to provide a concentration of the peroxygen-releasing compound of 0.002% to 1%, based on the total weight of the fermentation broth.

17. The method of claim 1 further comprising following the contacting step, adding a peroxygen-releasing compound to the product of the contacting step.

18. The method of claim 1 wherein the step of providing the fermentable sugar comprises producing and storing a carbohydrate feedstock wherein the peroxygen-releasing compound is added to the carbohydrate feedstock and wherein the carbohydrate feedstock comprises a fermentable sugar and further wherein the carbohydrate content of the feedstock is at least 1% by weight, based on the total feedstock weight and the peroxygen-releasing compound is added in an amount to provide 0.0001 to 5% of the peroxygen-releasing compound, based on total weight of the feedstock.

19. The method of claim 18 wherein the carbohydrate content of the feedstock is 1 to 70% by weight, based on the total feedstock weight and the peroxygen-releasing compound is added in an amount to provide 0.001 to 1% of the peroxygen-releasing compound, based on total weight of the feedstock.

20. The method of claim 18 wherein the feedstock is a sugar-based feedstock.

21. The method of claim 18 wherein the feedstock is a cellulose feedstock.

22. A method according to claim 1 wherein the fermentation process further comprises after step (iv), adding the nitrogen-free peroxygen-releasing compound to the product of the contacting step which product comprises ethanol.

23. A method according to claim 1 wherein the fermentation process further comprises after step (iv), separating the ethanol from the product of the contacting step which product comprises ethanol to provide a remaining product, wherein the remaining product is fed, into a beer-well or a thin stillage tank and adding the a nitrogen-free peroxygen-releasing compound to the beer-well or thin stillage tank.