Correlation of Yeast Measurement between Hemocytometer, Spin-Down and Coulter Counter Laboratory Analysis with The McNab Cell Counter
By H.A.Teass, John Byrnes and Andrea Valentine McNab, Incorporated Mount Vernon, New York USA
Presented to the American Society of Brewing Chemists June 21-23, 1998
This poster addresses the use of an in-line, across-the-pipe analyzer to measure yeast cell count in brewery applications. New data is presented showing the correlation between the in-line McNab Cell Counter and ASBC hemocytometer analysis. Previously presented information is provided showing the correlation between the in-line instrumentation with ASBC spin-down 0-50% and Coulter counter laboratory analysis.
Cell concentration levels at various stages of the brewing process are ultra-high, with concentrations as high as 2 billion cells/ml being typical in such areas as the pitching line and at the bottom of fermentation vessels.
The McNab HSA4 in-line cell counter eliminates common sampling and dilution errors sometimes found in the laboratory, and replaces the necessity and expense of tedious laboratory analysis using hemocytometer, spin-down and Coulter Counter methods. Optical adjustments have improved the accuracy of the cell counter from 70% to 98% as compared to lab methods, making this analyzer suitable for controlling feed-forward and feed-back control loops involving cell cropping, pitch blending and yeast transfer.
The HSA4 uses a near-infrared radiation signal and is designed to be mounted directly in the pipe line typically 2 to 6 inches (50 - l50mm) in diameter. This cell counter allows the brewer to better control yeast content so as to meet specifications, improve uniformity of fermentations, and enhance filtering operations.
There have been different process analytic methods for measuring or counting yeast levels in pipes in the brewery. One system uses a minute shift in radio frequency "phase angle" caused by the presence of the yeast cell wall structure.
Other designs have used turbidity meters to measure the loss of light, which will be somewhat inversely proportional to the concentration of yeast. Such measurements are typically non-linear.
The optical instrument used here is not a turbidimeter. To achieve proper results as described above, an optical instrument must be free of typical turbidity problems such as beer color interference. There must be a single pre-determined linear relationship between the cells and the meter indicating output. Further, there needs to be clear moisture-free (non-fogging) optics and automatic compensation for tungsten filament bulb drift (quasi-double beam correction). These optical particle counter meters are only recently available to the brewing community.
The equipment used in this test is the McNab Model HSA4. The HSA4 allows for the accurate measurement of yeast particles through the use of selective narrow-band NIR absorption methods using advanced optical technologies, modern electronics and proprietary algorithms. A special absorption band is chosen to measure yeast cell concentration and suppress unwanted interferences. The computation to determine concentration is based upon an enhanced Lambert-Beer law, where NIR absorption is proportional to the concentration of yeast.
The overall objective of this research was to measure the HSA4's correlation with laboratorv analysis methods in the determination of yeast concentration. Specifically this research shows how the HSA4 can measure in-line:
To ensure accuracy; the in-line yeast counting sensor and its indicator were moved to the laboratory. The samples were then introduced into the full diameter pipe and agitated to maintain suspension. The readings were then compared to the following laboratory methods to ascertain correlation.
Yeast cell concentration in cells/ml was measured by direct cell counts using the ASBC hemocytometer yeast cell concentration procedure.
Yeast concentration as percent-solids was measured using the ASBC spin down method.
Yeast concentration in yeast cells/ml was measured using a Coulter counter (particles 3 microns and larger were considered yeast).
The same HSA4 equipment was used for these tests. The lower correlation in the Figure 2, Hemocytometer, may be due to the lower repeatability in the laboratory method due to multiple dilutions.
The data shown here demonstrates that the HSA4 instrument closely corresponds to the measurements provided by typically used laboratory analysis. This would suggest that the instrument can be used to provide the same – or better – control of the brewing process than that provided by tedious laboratory analysis.
McNab cell counters provide accurate, real-time measurements of yeast content in the process brewing line to provide the brewmaster with:
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