Fermentation is a highly complex process. Many parameters can affect the final alcohol content and overall yield. Today, most distilleries or fuel ethanol plants use high performance liquid chromatography (HPLC) for fermentation monitoring, including acids, sugars, alcohol and glycerol measurements. All these components are interrelated. It is therefore essential to be able to track them at each stage of the fermentation process. There are disadvantages in using HPLC as the primary monitoring tool.
Disadvantages of Using HPLC
The disadvantages of using HPLC are:
- It is time consuming.
- The sample analysis takes at least 20 minutes, not including the sample preparation, instrument calibration and the after analysis wash-out time. This generally lead to the actual incapability to keep up with the demand for fermentation sample results.
- It cannot be used as a real-time trouble-shooting tool. Potential problems occurring in the early stage of the process cannot be identified until the yield is compromised.
- It can analyze only soluble components.
- To extract the components of interest from the mash, this must be centrifuged or filtered to retain the liquid portion. This can lead to errors in the analysis, since the removed solid portion contains sugars, acids, and alcohols, thus making the results inaccurate.
- The technician must be highly skilled.
- Accessories (e.g. columns, chemicals, filters) can be quite expensive.
NIR Analysis
Fermentation sample can be analyzed in a glass beak in diffuse reflectance mode using Bruker Optics MPA integrating sphere channel or MATRIX-I system mounted with off-center rotator. They are exclusively designed for inhomogeneous sample analysis. The predictive errors of the calibration models that Bruker currently use to monitor corn fermentations in distillery are shown in Table 1.
Table 1. RMSECV values for fermentation parameters,
| Component |
Approximate RMSECV |
| Ethanol |
0.14 |
| Dextrins |
0.5 |
| Dextrose |
0.46 |
| Maltose |
0.52 |
| Lactic Acid |
0.11 |
| Glycerol |
0.07 |
Troubleshooting of NIR Spectrometer
Over the course of one year, one lab technician can measure 5600 corn mash samples with just one NIR spectrometer. The fermentor can be monitored at 12 to 40 h intervals and the final percentage of alcohol can be predicted. In case the values are lower than expected, corrective actions can be undertaken. Troubleshooting of fermentors is performed by verifying whether the correct amount of enzyme or yeast was added or auditing the plant for mechanical failures.
An example of a mechanical failure is an increase in lactic acid and a decrease in ethanol in one fermentor, generally caused by the Butterworth washer not rotating properly. Another example is the presence of leaks in the cooling coil which leads to a low alcohol content.
Advantages of NIR Analysis
The advantages of NIR analysis are:
- It is a rapid. In each measurement (which last roughly only 1 minute) multiple components can be simultaneously determined.
- It is non-destructive. Fermentation samples can be studied directly, since no sample preparation is required. No waste and pollution are created.
- It is simple, highly precise and accurate.
- NIR technology can assist in identifying and fixing potential problems before the yield is compromised.
- NIR spectroscopy is an asset that allows distillery and fuel ethanol plant to rapidly perform research on different protocols to optimize the fermentation process by changing enzymes, parameters or nutritional supplements.
- NIR analysis ensures considerable savings in raw materials, processing fuel, steam, labour, maintenance and equipment.
- Troubleshooting is a major advantage of a NIR spectrometer.
Significant Savings Using NIR Spectrometer
The following example shows the significant savings associated with the use of a NIR spectrometer. If the fermentor is 200,000 l and the average fermentation finishes when alcohol content reaches 9.6%, this means that the plant will produce 19,200 absolute liters of alcohol per fermentor. Using NIR, if after the fermentation optimization, the average alcohol content is raised to 10.6% for each fermentor, then 21,200 absolute liters of alcohol are made in each fermentor. If 1000 fermentors are set per year in a plant to produce a certain amount of alcohol, the one percentage point increase in fermentor alcohol content means that the plant can now set only 905 instead of 1000 fermentors to produce the same amount of alcohol.
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This information has been sourced, reviewed and adapted from materials provided by Bruker Optics.
For more information on this source, please visit Bruker Optics.