Effective yeast and CO2 removal for beer QC

Acidity is a parameter that affects the beer production process at every stage. Adjusting the pH optimizes alcohol content, flavor, and stability of the final product. Brewers frequently check and, if necessary, adjust the pH to ensure a consistent product.
Measuring total acidity, however, first requires CO2 and yeast removal from the sample. This is commonly achieved by filtering beer.

What is total acidity?

Total acidity refers to the sum of all acids in fermented beer after carbon dioxide removal. These acids can originate from the mash or the fermentation process. Total acidity is an important indicator of pH—and therefore flavor—of bottled beer.

The pH of finished beers varies by type of beer. But generally, it lies between pH 3 and 5, with the majority being between pH 4 and 4.5. The pH of the final product has a large impact on the value of beer due to its effect on taste, foam stability, and shelf life.

How is total acidity determined?

Several international organizations publish recommendations on quality control (QC) standards for sampling, sample filtration, and analysis of malt, wort, and beer. These organizations include the European Brewing Convention (EBC), Mitteleuropäische Brautechnische Analysenkommission (MEBAK™), and the American Society of Brewing Chemists (ASBC).

ASBC method Beer-8 sets out guidelines for determining the total acidity of beer. During fermentation, yeast produces CO2 as a by-product of alcohol formation. A proportion of this CO2 dissolves in the beer. To obtain an unbiased measurement in the Beer-8 test following fermentation, analysts first remove yeast and CO2.

How do analysts remove yeast and CO2 for QC?

A common method for removing both yeast and CO2 from fermented beer is to pass the sample through a paper filter. Different beer filter grades will have different particle retention sizes. Analysts should select the most appropriate grade for their requirements to ensure the validity of the analysis.

To assess the suitability of different filter papers for QC sample preparation, researchers at the Biotechnology School at Jiangnan University, Jiangsu, China, tested three grades of Whatman brand filter paper for their ability to remove yeast and CO2 by gravity filtration.

The papers tested were Whatman Grade 2V, Grade 597½, and Grade 2555½. The researchers determined CO2 removal by comparing dissolved CO2 in samples filtered by ASBC method Beer-1,D (decarbonation by rotary shaker) to unfiltered samples (Table 1). Yeast removal efficacy was determined by checking concentration of yeast in suspension before and after filtration (Table 2).

The results demonstrate that all three filters are effective at filtering yeast and CO2. Whatman Grade 2V stands out as particularly suitable, removing over 75% of CO2 and over 99.99% of yeast cells.

Analysts looking to use a single grade of filter to remove both yeast and CO2 can use these data to aid their filter paper selection. Maximizing the effectiveness of CO2 and yeast removal will assist in improving accuracy in total acidity measurements, and ultimately help the brewer to ensure consistent flavor.

Table 1. CO2 removal from bottled beer. Results are average of triplicate measurements

Filter grade
CO2 (mg/ml) CO2 removed (mg/ml) % removal
Unfiltered Filtered
2V
4.75
1.06 3.69 77.68
597½
1.94 2.81 59.16
2555½
2.07 2.68 56.42

 

Table 2. Yeast cell removal from fermented beer. Results are average of triplicate measurements

Filter grade
Yeast cells (number/ml) % removal
Before filtration After filtration
2V
2 x 107
1.9 x 103 99.991
597½
4.3 x 104 99.783
2555½
2.5 x 104 99.874
 

Resources

Application Note – Whatman filter papers for use in the beer industry (PDF).

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