Some say the optimal Brix is between 10-30, but I have done it at 20 Brix and the efficiency of fermentation was 137% (above standard level). Does anyone have any explanations?
Initial sucrose content is about 40 - 45 % and basically the density of molasses does not reflect the true value of sucrose content. However, the Brix value has been used traditionally, the optimal Brix value of the feeding Molasses should be about 15 - 25 depending upon the fermentation stage and metabolic state of the yeast.
How did you calculate the % efficiency? If it's 137%, it sounds like there may be something wrong with the data.
As you come to this value of 137%, usually in the fermentation efficiency is 90%. We know that the yeast does not make any sucrose in ethanol, part of the energy supplied by sucrose is used by the cell for survival. Review your calculations!!
Are u aware that the value given by a refractometer varies according the sample temperature? Type of fermentation? alcoholic? lactic or propionic? make sure you consider this as the T° and composition of the fermented sludge may influence recorded values!!! remember Brix measures the total dissolved solids [ which is mainly sugar , but also does include minerals]p. This measurement is from 0 to 32 Brix on most refractometers, but other refractometers can go to as high as 50 brix.
Roger et al. (2003) mesuring sugar found that the bias in the sugar content prediction was about 8° Brix for a temperature variation of 20 °C (http://www.sciencedirect.com/science/article/pii/S0169743903000510)
I totally agree with Roger Djoulde - If you are using refractometer then the value varies as mentioned.
Thank you all for the answers. Very helpful. I guess i have to measure the reduction sugar not only the Brix for the better calculation.. Best regards from me.
Dear Mr. Wulan: I think you should measure total sugar in molasses and also Brix value to use in the fermentation process and make your calculation accordingly.
When I was measuring ethanol production from glucose many years ago, I found that the yeast biomass produced was about 5% of the mass of glucose consumed. I also found that there glycerol was produced , which was also about 5% of the glucose consumed. These values resulted in obtaining about 90% of the "theoretical yield", i.e. the stoichiometric yield for the simplified chemical reaction: sugar -> ethanol + CO2.
Dear Mike how did u manage to mesure ethanol production?(chemical reaction? physical? densitometry? alcoholmeter) is it possible to have a reference?.
I used a YSI enzymatic analyser (http://www.ysilifesciences.com/) for both glucose and ethanol. You can also use gas chromatography, HPLC, or a "wet biochemistry" enzymatic kit (manufacturer I used no longer supplies these kits, so you'll have to search for one).
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