We are fermenting small samples of the energy crops harvested from each of the plots at the Kentucky State University Research Farm. Each of the 16 beakers in this picture contains a sample from a single plot. It is important that we keep the samples from each plot separate (rather than combining all of the sweet sorghum samples, for example) in order to measure the variability between plots for our statistical analysis. KSU student John Rodgers is adding an enzyme and heating the samples to break the starches down into fermentable sugars.

The samples were randomized, but the crops can be easily distinguished by the color of the mash. Corn is creamy white; sweet sorghum is pea-soup green; sweet potato is reddish-brown; and Jerusalem artichoke - a white root - is dark brown.

John used a refractometer to measure the soluble solid content of each mash. The amount that light bends when passing through each solution increases as the insoluble starch is changed to soluble sugar. The refractometer works by measuring the angle of refraction of light passing through a droplet of solution.

We used a hydrometer to measure the specific gravity of each wort (the liquid portion of the mash) before fermentation. The hydrometer floats higher in solutions with a higher sugar content. Sweet sorghum juice was about 20% sugar, so we had to dilute it to reduce the sugar content to the approximate level of the other samples (about 5% sugar). If we had fermented the sweet sorghum juice without diluting it then the high alchohol content would likely kill the yeast before all of the sugar had been converted to ethanol.

We placed each wort in a sealed flask with yeast to begin fermentation. A tube allows the carbon dioxide produced by fermentation to escape into a small flask of water. We can tell that fermentation is occurring by the carbon dioxide bubbles coming out of each tube.