Using combination Forward Scatter and 90° Haze Detection of filtered product as a predictor for "bits" in packaged beer

Model DSB

by RJ Klimovitz and John Byrnes

Presented at the Master Brewers Association of the Americas Annual Meeting, Anaheim, California USA  

Abstract

"Bit" formation can occur in beer subsequent to filtration and packaging, and this may affect the appearance of the product. It would be very desirable, at the output of the filter, to be able to immediately evaluate the batch's potential for eventual "bit" formation.

This poster presents data taken before and alter a three-month storage period at room temperature. Testing was done using simultaneous forward and 90° white-light scatter methods. A correlation was found between haze measured at 90° nephelometric scatter angle and "bit" presence three months later.  A lack of correlation between forward scatter measurement and subsequent "bit" presence was also found.

Where there is excessive 90° nephelometric haze, special action (such as special filtering or blending off) would be suggested to avoid subsequent bit formation.  This improves the perceived quality of the premier beer as seen by the customer some weeks after originally produced.  The beer haze was measured by a dual angle haze meter (Model DSB by McNab) based on ASBC or EBC methods.

Introduction

Packaged beer on the shelf eventually deteriorates in appearance and may develop "bits" as large as 1/16 of an inch in size.  To the consumer this appears as questionable quality.  ASBC and EBC refer to this as "physical stability" or "shelf life."  Earlier work has shown that concentrations of particles (certain proteins) less than 500 nm (1/2 micron) in size subsequently contributed to severe "bit" formation.

Pressure leaf filters are used extensively for removal of yeast from beer.  Typically they are designed to remove particles larger than 500 nm in size.  In addition, the efficiency of particle removal by the filter has been sometimes monitored by a haze meter using the forward scatter measuring angle, which is relatively insensitive to particles less than 500 nm in size.

In addition to the traditional on-line monitoring of yeast and filter aid (DE) concentration, it is very desirable to evaluate the filter output immediately to determine the batch's tendency to form "bits" (thus lowering shelf life).

Background

Beer filtration typically is monitored on-line by a haze (nephelometric or forward scatter) instrument measuring in the beer line just after the filter.  This instrument helps maintain low beer haze levels at the output of the filter. The operating principle is: Light is sent across the beer stream and particles present in the beer scatter this light. The scattered light is measured by detectors mounted at the pipe. The indicator/controller displays the haze value. Periodic system calibration maintains accuracy

The brewery is accustomed to seeing the measurement angle (from the axis of the light) of 90° (nephelometric method) or 165° (forward scatter).  At first viewing it would be logical to assume that the measurement angle used is of little significance. However, for very complex reasons, detection sensitivity to particle size significantly varies with the angle of measurement.  In some cases this sensitivity varies by more than 10:1.

In the filter process, the DE filter is, by design, less effective on particles under 500 nm in size. The haze instrument used to monitor the filter is also affected by particle size, depending on its measuring angle. The brewer needs to understand this interaction and select the instrument accordingly This poster presents an instrument and performance data for better understanding and reduction of "bit" formation.

Equipment

The test equipment used is the McNab Model DSB Analyzer. The Model DSB uses a unique dual optics design to simultaneously measure haze using both scatter measurement angles: 90° nephelometric and forward scatter.  The design uses a single light source and optical path to obtain both measurements. Since both measurements are made on the same volume of product, they are directly comparable.  The data is simultaneous, allowing comparison of forward scatter (e.g. PPM Silica) and 90° nephelometric (Fm per the ASBC) readings.

Figure 1 shows the change in gain due to the measuring angle in an instrument measuring scattered light.

Figure 2 shows the technique used by the Model DSB to simultaneously measure two light scatter angles, with complete compensation for any interferences.

Method & Objective

The haze instrument is mounted just after the beer filter; where the beer is at 32°F Out in the marketplace three months later; the customer sees the product. The question is: "Is there a correlation between high haze readings at the beer filter and shelf life?  if so, which scatter angle (90° or forward scatter) used in the on-line instrument will best accomplish this measurement?"

For this test, beer samples were selected and haze was measured at 32°F at the beginning of the test period.  Haze was again measured after a three-month storage period.  Initial measurements were at 32°F - typical temperature of the filter outlet.  Measurements after storage were made at both 32°F and 70°F to compare typical temperature at purchase.

In addition, the initial measurements were made using both 90° (nephelometric) and forward scatter angles.  Measurement after storage used forward scatter for increased sensitivity to "bits”: The data was then compared to find the best correlation between measurement angle and "bit" formation three months later.

Graphs

Graph 1 shows the 90° nephelometric haze measurement on fresh beer; at the time and temperature of filtration, and measurements after shelf storage. There is good correlation (0.93) between the "prediction" by the 90° DSB (Y axis) and the actual resulting haze formation (X axis) after storage. (The most desirable correlation would be 1.00).

Graph 2 shows the forward scatter haze measurement has very little ability to predict, with a low correlation (0.18).

Graphs 3 and 4 show the ability to predict "bit" formation (and shelf life) when the final measurement is made at 32°F instead of 70°F.  The results are similar, showing high resolution and correlation for the 90° measurement and low correlation for forward scatter.

Conclusions

The best correlation and predictability between the brewery filter reading and three-month haze is on a 90° nephelometric instrument.  These findings are consistent with previous work showing that the mechanism for "increased" particle size over time seems to be the “joining" of small particles, creating the larger more visible "bit" particles  (Ref 1 and 2).  Low 90° haze readings after filtration suggest a low concentration of protein size particles and less contribution to the larger "bit" formation over time (here three months).

The test data suggests that the dual angle DSB meter is the best choice to combine the monitoring functions.

It will both evaluate beer haze and alert the operator to make adjustments in filter operation for long-term visible particle stability – seen as "bits”.'

The DSB 90° scatter angle focuses its attention on the quality of the beer's particle concentration and eventual appearance for the consumer, an important factor in a very competitive marketplace. The forward scatter angle focuses its measurement on the quality of the filter process (e.g., is the D.E. cake intact?).  Hence the dual channel instrument contributes both to the process monitoring (filter operation) and quality control (beer shelf life) of the brewery.

References

1.  Wenn, R.V., Paterson, E. and Wheeler, R.E.,  PROCEEDINGS OF THE EUROPEAN BREWERY CONVENTION CONGRESS (19th), Formation of chemically induced and permanent hazes in beer, London, 1983, 315-322.
2. Byrnes, John & Valentine, Andrea, The Effect of Measurement Angle and Particle Size on Scattered Light in the Beer Line, McNab, Incorporated, A92-07

3. DSB Two-Angle Clarity Analyzer; McNab, Incorporated, A91-61

4. ANALYTICA-EBC (1 987) Fourth Edition, Brauen- und Getrenke-Rundschau, Zurich, 9.17, Prediction of Shelf Life.

5. METHODS OF ANALYSIS OF THE AMERICAN SOCIETY OF BREWING CHEMISTS, Beer-27, Beer Stability; Nephelometric Method

Acknowledgments

The authors acknowledge the support of The Stroh Brewery Company and McNab, Incorporated, Andrea Valentine and H. A. Teass.

Questions? Contact McNab

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