In order to maintain Australia's prominence as one of the world's leading beer drinking nations, measures were taken to ensure a competitive edge.

A number of parameters are measured by laboratory technicians to ensure that the quality of beer meets the satisfaction of the drinker. Among these parameters is Beer Foam analysis. Foam in a beer is produced once it is poured into a glass in a practical sense. In a laboratory situation, foam is produced in a test tube by the reproducable shaking of a beer sample. Traditionally, laboratory technicians would observe the beer sample and try to determine values for foam potential, the foam half life, and drainage. This procedure would be described as a Foam Assay.

The simplest and easiest method to assess the foaming properties of a beer sample, is to pour the beer into a glass and judge the foam quality (foamability, stability, and cling) with the naked eye. This is purely a subjective method however, and there are limitations to the procedure. As demonstrated by Haugsted et al, 1990, it is possible to utilize an image analysis system to perform the Foam Assay. The results are not only easily measured, but also reproducible.

Digital Video Analysis using Image Pro Plus and BEER Pro (an Image-Pro add-on software module developed by Scitech Pty Ltd.) has enabled this procedure to be performed automatically by performing time lapse video capture and image analysis.

The system consists of an apparatus for mounting and shaking the test tube, a Ѕ" scientific grade mono video camera, a video capture card, a uniform (backlit) fluorescent light source, Image-Pro Plus and BEER Pro.

The light source is mounted behind the test tube to enable a uniform background. The user selects the number of frames to be acquired, time interval per frame and, using the ROI tool, selects the portion of the image to be analysed. The thresholding tool is used to distiguish between the beer/foam and air/foam boundaries. One of the difficulties encountered was that beer foam had a tendency to cling to the sides of the test tube. This was adjusted for using the gain control of the camera. The backlighting helped in identification of the foam by making the foam appear dark. An Image-Pro calibration file was created to convert pixels to mls using a graduated test tube.

Once a series of images is acquired, BEER Pro creates a mosaic of the images (usually about 12 images) and computes the beer foam potential (the amount of beer foam in ml formed by the beer sample), foam halflife (the time taken in seconds to reach half the initial volume), and drainage (the amount of liquid in ml drained from the foam during the measuring period). The results are displayed in report form. A pseudo-colour representation [see bottom image] was also useful to easily distinguish between the media.

References: C Haugsted, M.B. Pedersen, and K Erdal

Submitted by:
Con Sapounas
Scitech Pty Ltd.
155 Plenty Rd.
Preston, South Victoria
3072 Australia
Email: cons@scitech.com.au
Tel: + 61 3 9480 4999
Fax: + 61 3 9416 9959

 
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