Using combination Forward Scatter and 90° Haze Detection of filtered product as a predictor for "bits" in packaged beer
RJ Klimovitz and John Byrnes
Presented at the Master Brewers Association of the Americas Annual Meeting, Anaheim, California USA
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.
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.
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
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).
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
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.
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.
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
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?"
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.
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).
shows the forward scatter haze measurement has very little ability
to predict, with a low correlation (0.18).
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.
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).
test data suggests that the dual angle DSB
meter is the best choice to combine the monitoring functions.
will both evaluate beer haze and alert the operator to make adjustments
in filter operation for long-term visible particle stability – seen as
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.
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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