Antimicrobial method for fermentation processes
A system and method for controlling bacteria, especially lactic and acetic acid bacteria in the production of ethanol using an organic oxidizing compound in combination with an inorganic oxidizer is provided. Particularly, a mixture of one or more peroxy acids and one or more peroxide compounds is introduced into a fermentation mash so as to inhibit or reduce levels of bacteria that compete with yeast for the fermentation sugars. The peroxy acid and peroxide compounds largely are consumed during the fermentation process and are generally not present in the fermentation by-products, especially recovered distiller's grains.
1. A method of controlling lactic acid levels within an ethanol fermentation system comprising:
introducing peracetic acid and hydrogen peroxide into a fermentation mash located within said ethanol fermentation system, wherein said peracetic acid is introduced into said fermentation mash at a level of less than 50 ppm and said hydrogen peroxide is introduced into said fermentation mash at a level of less than 50 ppm, wherein said fermentation mash comprises an aqueous suspension of fiber, wherein a first portion of said hydrogen peroxide is added to said fermentation mash prior to the introduction of said peracetic acid into said fermentation mash, and wherein said peracetic acid is introduced into said fermentation mash as a mixture with a second portion of said hydrogen peroxide; and
fermenting said fermentation mash with an ethanol-producing yeast, at least a portion of said peracetic acid and said hydrogen peroxide being present in said fermentation mash during said fermenting step at levels sufficient to prevent lactic acid levels within said system from exceeding 0.20% by weight of a liquid portion of said fermentation mash.
2. The method according to claim 1 , wherein said peracetic acid is introduced into said fermentation mash at a level of between 5 to 30 ppm.
3. The method according to claim 1 , wherein said hydrogen peroxide is introduced into said fermentation mash at a level of between 5 to 40 ppm.
4. The method according to claim 1 , wherein said system comprises a header, and a mash cooler, said fermentation mash being delivered into said mash cooler via said header, and said peracetic acid being introduced into said system in said header.
5. The method according to claim 1 , wherein said system comprises a fermentation tank, said peracetic acid being introduced into said system in said fermentation tank.
6. The method according to claim 1 , wherein said fermentation system further comprises a quantity of distiller's grain derived from said fermentation mash, wherein said method further comprises recovering said quantity of distiller's grain from said fermentation system, said distiller's grain comprising less than 1 ppm of said peracetic acid or said hydrogen peroxide.
7. The method according to claim 6 , wherein said distiller's grain is free of antibiotic compounds.
8. The method according to claim 1 , wherein said peracetic acid is provided as a mixture with a germicidal fatty acid.
9. The method according to claim 1 , wherein said fermentation mash is a corn mash.
10. The method according to claim 1 , said method being performed without the introduction of antibiotic compounds into said fermentation mash.
11. The method according to claim 1 , said ethanol fermentation system comprising:
at least one fermentation mash cooler;
a fermentation tank located downstream from said cooler; and
at least one injection station adapted to deliver a quantity of said peracetic acid and said hydrogen peroxide into said fermentation mash located within said ethanol fermentation system.
12. The method according to claim 11 , wherein said at least one fermentation mash cooler comprises a primary mash cooler and a secondary mash cooler.
13. The method according to claim 11 , wherein said at least one injection station comprises a header disposed between said primary and secondary mash coolers.
14. The method according to claim 11 , wherein said at least one injection state is adapted to deliver said peracetic acid and said hydrogen peroxide into said fermentation tank.
15. The method according to claim 11 , wherein said system further comprises separation equipment operable to recover a distiller's grain product from the fermentation mash exiting said fermentation tank.
16. The method according to claim 15 , wherein said distiller's grain product comprises less than 1 ppm of said peracetic acid.
17. The method according to claim 11 , wherein said injection station is adapted to deliver said peracetic acid into said fermentation mash at a level of between 5 to 30 ppm.
18. The method according to claim 11 , wherein said injection station is adapted to deliver said hydrogen peroxide into said fermentation mash at a level of between 5 to 40 ppm.
19. The method according to claim 17 , wherein said peracetic acid is provided as a mixture with a germicidal fatty acid.
20. The method according to claim 1 , wherein said peracetic acid and said hydrogen peroxide are added to said fermentation mash as a mixture, wherein said mixture comprises 5% to 30% by weight of said peracetic acid and 15% to 55% by weight of said hydrogen peroxide.
21. The method according to claim 1 , wherein said peracetic acid and said hydrogen peroxide are introduced into said fermentation mash prior to the introduction of yeast.
22. The method according to claim 1 , wherein said fermentation mash further comprises a member selected from the group consisting of protein, oil, and combinations thereof.
23. The method according to claim 1 , wherein said hydrogen peroxide is added to said fermentation mash at a location within said ethanol fermentation system that is upstream from a location within said ethanol fermentation system at which said peracetic acid is introduced.
24. The method according to claim 1 , wherein said first portion comprises from about 12 ppm to about 35 ppm of said hydrogen peroxide.