LEARNING FROM FUEL ETHANOL W R I T T E N B Y R E A D E A . H U DDLESTON, M SC.
lead to off-flavors. They also have high installation costs, and operating jet cookers can be complicated and dangerous. Finally, they require specialized maintenance and significant support equipment to keep them operating at full capacity.
FERMENTATION
Fermentation for fuel ethanol has some striking differences from beverage ethanol. The goal of fuel ethanol fermentations is to produce the maximum amount of alcohol in the minimum amount of time. This means that most fuel ethanol fermentations will seem wildly high and out of control when compared to beverage fermentations. It is not LESSONS FROM A uncommon to see fermentations as high as 20 percent ABV in a plant scale fermentation and 23 percent ABV in lab tests in just a few days. SISTER INDUSTRY To accomplish these types of high-gravity, high-alcohol fermentations, fuel producers utilize a number of interesting tools and methods. The first of these methods is predictive fermentation management. Although many fuel ethanol producers use genetically modified yeast that can operate at much higher temperatures and alcohol contents than the standard beverage distiller’s yeast, they are still beholden to lmost every distiller knows that ethanol can be used as fuel. Indeed, the fundamentals of yeast biology. That means that if yeast get too hot there are probably quite a few lawnmowers or hedge-cutters that or cold, or run out of a vital nutrient they are likely to die out and cause have been modified to run on excess ethanol from stills. However, what a stuck fermentation. For fuel producers, a single stuck fermentation few beverage distillers realize is that fuel ethanol producers are some could result in thousands, if not millions, of dollars of loss, so it is vital of the largest distilleries in the world, and that they have made serious that they prevent them. Many fuel producers will use computer models advancements in the art and process of distillation. There is a lot that of fermentations to predict possible problems before they can occur. beverage producers can learn from the fuel industry, and These models can tell them when to raise or lower the temthe goal of this article is to highlight some of their more Fuel ethanol perature and when the perfect time will be to add nutrient. interesting innovations and methods. Another way that yeast can get overwhelmed is if they producers are exposed to too much sugar too quickly. This is espeCOOKING GRAIN are some of cially likely early in the fermentation when the yeast is just coming out of the lag phase and are exposed to the One of the basic differences between beverage and the largest large amounts of sugar available in fresh mash. In order to fuel ethanol producers is how they each handle mashing. distilleries combat this problem, fuel ethanol producers will often not Like beverage alcohol producers, fuel ethanol producers must cook their grains in order to gelatinize the starches in the world dose all of their enzyme into the mash. Instead, they will add some during mashing and then slowly dose the enand make them available for saccharification. However, and have zyme during fermentation to maintain a consistent sugar unlike beverage alcohol producers, which commonly use either a mash tun or cereal cooker to accomplish made serious level. This helps to keep the osmotic stress of the fermentation down and ensures healthy yeast. this, fuel producers prefer to use something called a jet advancements Finally, fuel ethanol producers also monitor and concooker. trol infections differently from most beverage distillers. In in the art and A jet cooker, also called a hydroheater, is a piece of equipment that mixes steam with grain slurry to create process of most beverage distillation plants, infection by lactic acid bacteria and other microbes is rather common and somea high-shear and high-pressure environment. Jet cookdistillation. times even desirable. Beverage distillers tend to monitor ers can operate at temperatures in excess of 120 degrees for infections using organoleptic testing and rarely, if ever, Celsius and their high-shear nature causes the starch plate samples for identification. Conversely, for fuel ethanol producers granules in grain to literally rip open. This helps to expose the maxiany level of infection represents lost yield and therefore money; which mum amount of starch granules to saccharification enzymes, and jet means it must be dealt with. Fuel ethanol producers are constantly cookers are extremely efficient at processing large amounts of grain in monitoring for infection and have recently begun adopting handheld very short periods of time. DNA sequencers, such as the MinION by Nanopore, to screen tanks Although jet cookers are incredibly important for fuel ethanol profor bacterial infection. If a fuel ethanol producer discovers an infection ducers, they have not yet gained popularity with beverage producers within a tank, they will often use antibacterial agents such as penicillin for several reasons. Firstly, because jet cookers operate at very high to try and eradicate it before it can spread. temperatures there is a possibility of scorching the grain, which could
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