How to prevent yeast (S. cerevisiae) from other microbial contaminants during fuel ethanol fermentation? – The Catalysts Group

How to prevent yeast (S. cerevisiae) from other microbial contaminants during fuel ethanol fermentation?

cerevisiae is one of most common & heart loving microorganism for fuel ethanol producing distillers. All the distillers want maximum productivity of ethanol by using their own culture or by using active dry yeast (ADY) to some extent. In day-to-day operations, Distillers try to implement the desired precautionary measures to prevent the cross contamination of either bacterial cells or wild yeast to their culture either during propagation or fermentation. This strict practice not only helps in preventing the sugar loss but also helps in achieving the desired ethanol yield. Due to involvement of unskilled labourers & their handling efficiency; surrounding environmental conditions; improper storage & sugary nature of feedstock; and limitation of sterilised conditions/CIP, leaves the door open for trouble such as stuck fermentation, high by-products formation & yield loss.

Sources of bacterial contaminations in Sugarcane based ethanol fermentation

Feedstock Contaminants Source
B & C Molasses High Lactic/Butyric bacteria Unhygienic storage
Cane Juice & Syrup Lactic acid bacteria/Bacillus/ Leuconostoc mesenteroides Soil contact and perishable feedstock

Type of by-products produced by different microbial contaminations

Organic Acids /Volatile acids Max. Permissible Concentration Causing Agents Genera / Species
Acetic acid 3500 ppm Acetobacter /Gluconobacter
Propionic acid 150 ppm Propionibacterium
Iso butyric acid 150 ppm Bacillus subtilis, Clostridium butyricum
n – butyric acid 150 ppm Clostridium acetobutylicum
Iso-Valeric acid 250 ppm Propionibacterium, Wild yeasts
Valeric acid 250 ppm Wild yeasts
Lactic Acid N/A Lactobacillus

Effect of microbial contamination

  • Affecting yeast growth and metabolism
  • Reduction in fermentation efficiency
  • Economic losses due to loss of fermentable sugars
  • High levels of by-product
  • Varying organoleptic properties
  • Affects spirit quality

Losses quantification from microbial contamination

Bacterial Counts Level                                                              EtOH loss v/v

Up to 1 million cells/ml                                                            up to 1%

1 million to 10 million cells/ml                                               1 to 3%

10 million to 100 million cells/ml                                          3 to 5%

More than 100 million cells/ml                                              > 5%

Types of microbial contaminants that create problem during fermentation: 

1-General bacteria found in surroundings like air, water & soil

2-Bacteria’s grow on sugary medium

3- Bacteria’s present in dead pockets & recycle streams have organic acids

4-Lactobacillus strains

5-Wild yeasts

Solutions offered by Catalysts Biotechnologies Pvt. Ltd.

  • Enzypro M: Molasses have a variety of complex sugars in it. These sugars are: dextran, starch, Beta-glucans, cellulose, etc., which are complex in nature and not utilized by yeast in such complex form. These sugars are made up of many glucose units bound together by different types of glycosidic bonds. So, we developed an imitable product with cocktail of required enzymes, which hydrolyse all the complex sugars and convert them into simple sugar i.e., glucose. This excess glucose is then available for yeast to produce more ethanol thereby enhancing the recovery.
  • Enzytreat Plus: A specific blend of antimicrobial agents, which efficiently controls wide variety of microbes in the industrial process environment. Enzytreat Plus is fast-acting biocidal agent with a moderately long duration of action. It prevents the proliferation of bacterial cell and mold cells by disruption of intermolecular interactions; results in dissociation of cellular membrane lipid bilayers, which compromises cellular permeability controls and induces leakage of cellular contents. 
  • Bactoferm: An efficient product to control the undesirable lactic acid producing bacterial contamination such as lactobacillus, leuconostoc, etc. Lactic acid production during propagation and/or fermentation not only causes the loss of sugar due to bacterial consumption but also creates the metabolic stress on yeast cell resulting in the lower ethanol yield and sometimes ceases the fermentation in mid process. 
  • Catalysts ADY: A high alcohol tolerance, osmotic stress tolerance & highly suitable yeast to obtain high gravity ethanol fermentation using cane juice syrup as a feedstock. Reduces the chances of contamination & wild yeast development due to multistep culture propagation.
  • DSPN- M: A nutritional strategy for yeast to enhance the ability of handling the variety of chemical stresses and to increase the metabolic process during reproduction and fermentation both. It also helps to provide the all desired vital nutrients for maximum productivity & health maintenance of yeast during entire process.