Beer quality control: Wort filtration

Many factors influence the beer brewing process and the quality of the final product. Wort filtration aids in assessing malt quality and reducing beer turbidity for downstream quality control (QC) analysis. This step enables manufacturers to manage product consistency and quality in line with their requirements.

Which factors determine quality during the brewing process?

Color, alcoholic strength, flavor, and clarity are the key factors that determine beer quality. These are the characteristics customers consider when choosing beer. For a manufacturer, the combination of raw ingredients and the specifics of the brewing process determine these characteristics.

QC checks at various stages ensure that the beer production process is on track to deliver a product consistent with internal standards. Such checks also allow the manufacturer to adjust for natural variations in ingredients as required.

These QC checks rely on standards recommended by bodies such as European Brewing Convention (EBC), Mitteleuropäische Brautechnische Analysenkommission (MEBAK™), and the American Society of Brewing Chemists (ASBC). The published methods describe how to prepare samples for QC, for example, by filtration, and how to conduct the analysis.

Table 1 lists MEBAK analytical methods that require filtration steps. Among the most critical of these methods is preparation of wort –and intermediate product in the brewing process - for quality analysis.

How does wort filtration help to improve beer quality?

Most beers are manufactured using barley malt as a primary starch source. Wort is a mixture resulting from the breakdown of this starch to sugars still contains various proteins and debris that require removal by filtration.

A coarse filter removes larger debris, while a finer filter removes coagulated proteins. These proteins (or other similarly sized particles), if left unfiltered, can lead to an unwanted change in flavor. They might also precipitate at a later stage in the manufacturing process, affecting the clarity of the final product.

The filtration speed and turbidity of resulting filtrate are indicators of quality for the brewer. Slower filtration reflects lower wort solubility, enabling the brewer to judge the quality of the malt. The wort filtrate turbidity indicates the efficacy of filtration.

Photometric QC testing of wort, as described by the ASBC Malt-4 method, requires a sample with sufficiently low turbidity. This method determines the extract of the malt, which assists in predicting fermentable extract, total acidity, pH, color, viscosity, total nitrogen, and free amino nitrogen.

What grades of filter paper are suitable for wort filtration?

Gravity filtration using cellulose paper filters is well suited for both regular wort filtration and sample preparation for QC. Various grades of filter paper meet specifications, but the speed and effectiveness of filtration can vary.

In a study to evaluate wort filtration, researchers at the Biotechnology School at Jiangnan University, Jiangsu, China, used three grades of Whatman brand filter paper—Grade 2V, Grade 597½, and Grade 2555½.

The researchers prepared two batches of coarse-filtered wort, adjusted to known turbidity levels of 10 and 30 respectively, and filtered using the three grades of filter paper. The study recorded turbidity before and after filtration, as shown in Table 2.

The results indicate that all tested filter papers are suitable for wort filtration. Grade 2V showed the greatest reduction in turbidity, potentially improving the accuracy of photometric analysis. However, it required a longer filtration time (up to 413 s vs 83 s and 52 s for Grades 597½ and 2555½, respectively).

These data demonstrate the use of three suitable grades of cellulose filter paper for wort filtration. The specific choice of filter paper depends on the individual brewer’s requirements in terms of time and quality.

Table 1. MEBAK analytical methods that use filtration

1.4.3.1 Soluble extract in wet spent grains obtained by pressing (rapid method)
1.4.3.2 Soluble extract in wet and dry spent grains obtained by rinsing (EBC)
1.4.4.2 Available residual extract
1.4.5 Iodine value of brewery spent grains
1.6.1 Solids in wort (Labor veritas method)
1.6.2 Solids or trub material (Field method)
1.6.3 Cold trub
2.6.2 Coaguble nitrogen (thermal coagulation of protein)
2.6.3.1 Nitrogen fractionation (precipitation with magnesium sulfate)
2.6.3.2 Nitrogen fractionation (precipitation with phosphomolybdic acid)
2.8.1 Limit of attenuation in wort (fermentation tube method)
2.8.2 Limit of attenuation in wort (reference method - EBC)
2.8.3 Limit of attenuation in wort (rapid method - EBC)
2.9.1 Degassing a sample (EBC)
2.10.3.2.1 Total glucose - hydrolysis method
2.12.2 Spectrophotometric (EBC)
2.14.2.2 Alcohol chill haze test, CHAPON (cold sensitivity)
2.16.3 Tannoids
2.17.3 Determination of hop bitter substances in wort and beer (EBC)
2.20.1 Membrane filterability test of beer
2.21.3.3 4-vinyl guaiacol and 4-vinyl phenol detection
2.21.8.3 Detection of SO2 with continuous flow rate
2.22.1 Chloride, sulfate, nitrate and phosphate in beer (EBC)
2.22.5 Sulfate ions
  Table 2. Turbidity reduction for wort batches by three grades of filter paper. Results are average of triplicate measurements

 

Whatman filter grade
Initial turbidity Turbidity after filtration Turbidity reduction (%)
Batch 1 Batch 2 Batch 1 Batch 2 Batch 1 Batch 2
2V
10.6
30.1 6.54 6.39 38.3 78.8
597½
8.02 7.25 24.3 75.9
2555½
7.24 8.96 31.7 70.2
 

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