Size Distribution and its Effect on Particle Measurement in the Beer Line

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Model DSB

A technical poster by John Byrnes and Andrea Valentine, of McNab, Inc.

Presented at the Master Brewers Association of the Americas Annual Meeting, Portland, Oregon USA

Abstract

Particle size influences both beer D.E. filterability and subsequent shelf life. The actual concentration level of small haze particles (< 1/2 micron) is often not measured. These small particles are considered difficult to filter. In this work, particle size distribution was measured in the laboratory on a variety of sample beers. The samples were then measured using a new in-pipe dual angle particle counter. There is a greater variation in the concentration of small particles than would be expected. The data show actual examples of variation that occurs in finished product, and compares measurements from the dual angle analyzer.

The data demonstrate the ability to measure a wide range of particles in the beer pipe. The dual angle analyzer shows the ability to measure very small particles in-pipe. Results show good correlation between the dual angle analyzer and laboratory particle size measurement. The small particle concentration should be considered regarding wort and beer composition, filterability and beer shelf life.

Introduction

One description of beer before filtration describes the suspended solids as large and small-with a typical dividing-line of 1/2 to 1 micron-where most larger particles arc removed by a pressure leaf filter while particles smaller than 1/2 micron arc sometimes thought to pass through the filter. There is now an awareness that smaller particles play an important part in the relationship of particle size, filterability and the duration of D.E. (diatomaceous earth) filter cycles. Far from being '"unfilterable," small particles play a major role in shortening filter cycles (see Posada). In this work we studied whether small particles arc present in significant quantities in beer, and whether they can be measured in the pipe.

This particle size information has potential value in these areas:

• detection of fine hazes that may be visible and therefore require corrective action.
• predicting shelf life, which can be shortened by high concentrations of small particles.
• monitoring overall performance of the filter.
• predicting filterability.

Objectives

Small Particles, Filterability and Corrective Action

Premature filter shutdown is often due to high delta-P (outlet pressure minus inlet pressure). This can be due to clogging of the filter pores with small proteins, dextrins, beta-glucans (see Bamforth), etc. Detection of beer with low expected filterability allows the operator to take corrective action to prevent premature filter shutdown. This can include treatment with fining agents, blending off, changing the filter aid to cause finer filtration (see Glastonbury), or postponing the filtration of the low-expected filterability batch until after the filtration of other high-expected filterability batches, when the filter run is almost complete anyway

In addition to the threat of shortened filter cycles, previous work (see Wenn et al. and Klimovitz et al.) shows that a high concentration of smaller particles correlates with subsequent formation of large particles in packaged beer, which has a negative impact on beer shelf life.

Equipment

The test equipment used is a McNab Model DSB in-pipe particle concentration analyzer and a bench-top scanning liquid particle counter using a laser diode as a source. The Model DSB (see Illustration 1) simultaneously measures beer haze using two separate scatter measurement angles, "90 degree" Nephelometric (per the ASBC) and "forward scatter" (11-13 degree). This design uses a single light source and optical path to obtain both measurements (see Illustration 2).

Method

Five different beer samples were measured using the liquid particle counter. A particle size distribution was generated for each sample. The beer samples were then measured by the Model DSB, which made simultaneous measurements of both "90 degree" and "forward scatter" haze in beer. The forward scatter is often calibrated using SiO2, but there are no published standards for forward scatter calibration. For this test, both the 90 degree and forward scatter measurements were calibrated using the formazin method per Methods of Analysis of the ASBC.

For each beer sample, the RS channel (forward scatter) and the HSB channel (90 degree) measurements were recorded. The particle size distribution graph is shown, with readings from the RS channel and the HSB channel denoted beneath each graph.

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figures 1 through 5 show the particle size distribution generated from the five samples. Figure 1 shows a high concentration of relatively large particles (over 7 microns in size). The corresponding reading of the HSB channel (90 degree) is 146, lower than the corresponding RS channel (forward scatter) reading of greater than 200.

The typical particle size is progressively smaller in Samples 2 through 5, until in Sample 5,60% of the particles are under 1 micron in size. For Sample 5, the HSB channel reading was 105, and the RS channel reading was 29. The HSB channel reading has increased significantly relative to the RS channel as particle size has decreased.

Conclusions

1. The dual channel Model DSB instrument detected significant levels of small particles in filtered beer.
2. The Model DSB correlates with separate laboratory analysis of particle size distribution.
3. The short, instantaneous analysis time from the Model DSB gives enough warning, previously not possible, for corrective action when small particles are detected.
4. Haze measurements by the Model DSB can be used to immediately detect high concentrations of large particles as well as small particles. Concentrations of large particles indicate an upset in the pressure filter "cake" and bleed-through of D.E.

Work in this area is continuing with measurements in the brewery in actual beer filter pipes.

References:

Wenn, R.V., Wheeler R.E., and Webb, DJ, "The prediction of high haze levels in freshly filtered lager beers responsible for the generation of "invisible" hazes and of "bits" in fresh bottled lager," (Proceedings of the European Brewery Convention 22nd Congress, Zurich, 1989), pp. 617-624

Klimovitz, RJ. and Byrnes, J., Using Combination Forward Scatter And 90° Degree Haze Detection Of Filtered Product As A Predictor For "Bits" In Packaged Beer., A93-48,1994

Methods of Analysis of the American Society of Brewing Chemists, Seventh revised edition, American Society of Brewing Chemists, 1987

PosadaJ., BREWING SCIENCE, Volume 3, edited by Pollock, J.R.A, Academic Press, 1987

Glastonbury, R., Pecar, M. and Roupas, G., Using The Coulter Counter For Process Optimisation, GB Brewtech, 1994

Bamforth, C.W, BREWERS DIGEST, 6-Glucan and 6-Glucanases in Mailing and Brewing:

Practical Aspects, May 1994

Timmermans, P., MBAA TECHNICAL QUARTERLY, Determination of the Filterability of Beer, Vol. 31, pp. 76-77.1994

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