Determination of Nitrogen/Protein in Beer (FP928)

Importance of the Topic

Determination of nitrogen in beer is crucial for calculating protein content using a conversion factor. Protein level influences beer quality attributes such as foam stability, clarity, and yeast viability. Monitoring protein during brewing supports consistency, process control, and final product quality.

Objectives and Study Overview

This application note demonstrates the use of the LECO FP928 macro combustion nitrogen determinator to quantify nitrogen in beer samples. The study evaluates performance parameters including carrier gas type (helium or argon), aliquot loop size, and method precision across representative beer styles.

Methodology

Samples are degassed at room temperature following AOAC 920.49. Approximately 1 g of sample or calibration solution is placed in ceramic combustion boats. Combustion is performed in a pure oxygen atmosphere at 1100 °C. Combustion gases pass through a thermoelectric cooler and ballast before aliquots are transferred into a carrier gas stream. A reduction tube with copper converts NOx to N2. Nitrogen is detected by thermal conductivity using either helium or argon as carrier gas. Calibration and drift correction are performed with glycine solutions and verified with ammonium standards. Key method parameters include purge cycles, ballast equilibration, and integration timing configured per carrier gas and aliquot size.

Used Instrumentation

• LECO FP928 Macro Combustion Nitrogen/Protein Determinator
• Ceramic combustion boats with nickel liners
• Thermoelectric cooler and ballast gas handling system
• Carrier gases: helium or argon
• Thermal conductivity detector and copper reduction tube

Key Results and Discussion

Precision and accuracy were assessed using three beer styles (porter, American IPA, Pilsner). A 10 cm3 helium aliquot loop provided the best precision at low nitrogen levels. Average nitrogen content ranged from 0.032 % to 0.111 % and translated to protein concentrations consistent with expectations. Relative standard deviations were below 1 % for helium and slightly higher for argon. The 3 cm3 loop extended reagent life while maintaining acceptable precision. Sensitivity decreased with argon due to lower thermal conductivity contrast.

Benefits and Practical Applications

• Rapid and robust nitrogen determination with minimal sample preparation
• Flexible configuration for sensitivity or reagent economy via loop size selection
• Reliable quality control tool for brewing operations and R&D laboratories
• Compliance with standard methods using traceable calibration

Future Trends and Opportunities

Advancements may include integration with automation and data management for real-time monitoring. Development of more selective detectors or chemistries could enhance sensitivity with alternative carrier gases. Expanding applications to complex matrices and inline measurement in brewing installations represent promising directions.

Conclusion

The LECO FP928 method delivers accurate, precise nitrogen and protein determination in beer. Choice of carrier gas and aliquot loop size enables optimization based on analytical requirements. This protocol supports quality assurance and process control in brewing environments.

References

• AOAC Official Method 920.49 Beer Preparation of Sample
• USDA Circular No. 183 Protein Factor Determination
• LECO FP928 Operator Instruction Manual