NOVELTY - Process (P1) for controlling unwanted bacteria in reaction process mediated by non-bacterial system reactive agents, comprises: taking a first portion of biomass feed and identifying the most abundant unwanted bacteria in the portion; culturing the first portion to increase the number of some of the unwanted bacteria to a level to provide sufficient unwanted bacteria to produce by lyse with bacteriophage an amount to provide a concentration of bacteriophage of at least 1x 104 plaque forming unit (pfu); and adding the bacteriophage to the biomass portion and mixing the first portion.    USE - The process is useful for controlling unwanted bacteria in a reaction process mediated by non-bacterial system reactive agents, where the unwanted bacteria for producing biofuel such as ethanol: comprise lactic acid bacteria including Lactobacillus, Pediococcus, Lactococcus, Enterococcus, Weissella, Leuconostoc, Streptococcus, and Oenococcus, or acetic acid bacteria including Acetobacter and Gluconobacter; or are bacteria other than lactic acid bacteria or acetic acid bacteria (all claimed).    ADVANTAGE - The process: utilizes the phages that are natural ubiquitous bacteriolytic agents with extremely high host specificity, specifically kill target unwanted host bacteria without interacting with non-bacterial microorganisms (such as yeast or algae) responsible for alcohol or oil production, and lead to both immediate economic and long-term socioeconomic impacts; and provides improved fermentation efficiencies, reduced wastes and reduced antibiotic residue in solid byproducts, thus increasing the yield of biofuel.    DETAILED DESCRIPTION - Process (P1) for controlling unwanted bacteria in a reaction process mediated by non-bacterial system reactive agents, comprises: taking a first portion of biomass feed from the total feed to the process and identifying the most abundant unwanted bacteria in the portion; culturing the first portion to increase the number of some of the most abundant unwanted bacteria to a level to provide (when reacted with bacteriophage virulent for at least one of the unwanted bacteria) sufficient unwanted bacteria to produce by lyse with bacteriophage virulent for some of the unwanted bacteria sufficient bacteriophage (when mixed with the remaining biomass feed to the reaction process) an amount to provide a concentration of bacteriophage of at least 1x 104 plaque forming unit (pfu); and adding the bacteriophage to the biomass portion and mixing the first portion so processed by culturing and adding virulent bacteriophage with the remaining portion of biomass prior to reaction in the reaction process. INDEPENDENT CLAIMS are also included for:    (1) a process (P2) for controlling unwanted biofilm producing bacteria in a reaction process mediated by non-bacterial system reactive agents, comprising supplying to the reaction process a solution of bacteriophage virulent for biofilm producing bacteria to reduce the level of the biofilm producing bacteria; and    (2) a composition comprising at least one bacteriophage virulent for unwanted bacteria in a biofuel production process comprising the first portion so processed by culturing and adding virulent bacteriophage.