Introduction
Distillery processes are well-suited for NIR analysis from the unloading of raw materials to the final bottling. The most important components in distillation are moisture, protein, oil, and starch, all suitable and proven measurable constituents using NIR spectroscopy. The moisture content of incoming grain is of critical importance. Moisture should not be above 15% in grain used for distillation because it can cause mechanical problems in the distillery hammer mill and reduces the starch content available for alcohol production. Protein content is important because it affects the composition of Distillers Dried Grains with Solubles (DDGS), a valuable by-product at the end of distillation. In general, high oil content in corn is considered disadvantageous for alcohol distillation as well as oil manufacturing because of reduced yield. Starch is the constituent with the greatest effect on overall yield because it is the source for fermentable sugars for yeast growth and subsequent alcohol production. There are many advantages to using NIR spectroscopy for these measurements in incoming grain. NIR not only provides a fast, cost-effective and non-invasive method, but it can also be used to measure multiple points in an incoming batch. The potential exists for fraud by placing low-quality corn at the bottom of a batch and high quality at the top. Checking multiple points in the batch with a spectrometer can help detect if this is the case. Other advantages include tracking production efficiencies, accumulating crop data, and having variety selection for desired characteristics of the incoming material.
Fermentation Monitoring
Fermentation monitoring is complex because multiple parameters affect the overall yield and final alcohol content. Most distilleries use HPLC as the method of choice for fermentation monitoring of parameters like sugars, acids, glycerol, and alcohol, all of which are interrelated during the fermentation process. While optimum efficiency can be accomplished if these parameters are kept in control, in practice this is difficult to do using HPLC. HPLC requires highly skilled technicians, expensive accessories, complex and time-consuming sample prep, and often does not produce results as accurate as required for optimum process control.
The potential improvements in fermentation that real-time monitoring using NIR spectroscopy can provide are immense. Optimization of protocols such as changing enzymes, process parameters, and nutritional supplements can increase the alcohol content per fermenter. Even a small increase in alcohol content per fermenter when a plant operates using hundreds of fermenters results in considerable savings in raw materials, steam, labor, processing fuel, maintenance, and equipment.
For example, if a two hundred thousand liter fermenter finishes the average fermentation at 9.6% alcohol, nineteen thousand two hundred liters of absolute alcohol is produced. If the process can be optimized to raise the alcohol content by 1% to 10.6%, twenty-one thousand and two hundred liters of absolute alcohol are produced. This means that a plant can have the same output of alcohol using nine hundred five fermenters instead of one thousand if the process is optimized, resulting in the potential for millions of dollars in savings per year. Studies have been conducted at a large distillery using these very methods to optimize fermentation. Fermentation time from ethanol content, sugars, and lactic acid have all been successfully monitored using NIR spectroscopy for optimization of the fermentation process. As with any food or beverage, adulteration is a big problem and NIR spectroscopy can be used as a screening tool for adulteration in alcoholic beverages.
References
Quality Analysis, Classification, and Authentication of Liquid Foods by Near-Infrared Spectroscopy: A Review of Recent Research Developments – Wang, Sun, Pu, and Cheng, Critical Reviews in Science and Nutrition, 2017, Vol. 57, No. 7, 1524-1538
https://www.tandfonline.com/doi/pdf/10.1080/10408398.2015.1115954
Livermore, Wang, and Jackson – The Alcohol Textbook, 4th Edition, Nottingham University Press, 2003, Chapter 12 – Understanding Near-Infrared Spectroscopy and its Applications in the Distillery, pp. 146-170
https://edisciplinas.usp.br/pluginfile.php/2993570/mod_resource/content/1/The_Alcohol_Textbook-%204%20Ed.pdf