Analysis of Acids in Beer

Beer's Acidity and Alkalinity

Beer is generally acidic, with most popular American beers having a pH between 4.0 and 5.0, which falls into the moderately acidic range. Sour beers are typically more acidic. Beer's acidity primarily comes from the fermentation process, where yeast converts sugars into alcohol and carbon dioxide, making the beer more sour.

Main Acids in Beer

Beer primarily contains the following organic acids:

• Acetic acid: imparts a vinegary flavor

• Pyruvic acid

• Lactic acid: imparts a yogurt-like flavor

• Malic acid

• Citric acid: imparts a sharp, sour flavor

These acids primarily originate from the raw materials, the wort boiling process, and yeast metabolism. Lactic and acetic acids can also result from unwanted or uncontrolled microbial contamination.

Sources of Beer Acidity

1. Malt

The acids in malt can be divided into those produced by biochemical reactions and those produced by saccharification. Malt acids are primarily phosphoric acid, followed by formic acid, acetic acid, propionic acid, citric acid, higher fatty acids, and various amino acids.

2. Water

The calcium and magnesium ions in water convert the alkaline K₂HPO₄ in the wort into acidic KH₂PO₄, increasing the wort's acidity and lowering its pH.

3. Acid Addition

During the wort preparation process, acid may be added to adjust the wort pH and condense the enzymes and proteins in the malt, possibly due to insufficient acid in the malt or excessive alkalinity in the brewing water.

4. Fermentation Process

Yeast metabolism not only produces ethanol, water, and CO2, but also volatile acids (such as acetic acid and butyric acid) and non-volatile acids (such as lactic acid and succinic acid). Acetic acid is the primary volatile acid and has the greatest impact on beer acidity. Succinic acid, the least volatile acid produced during beer fermentation, has a significant impact on beer acidity.

Methods for controlling beer acidity

1. Raw material control

• Use high-quality, mold-free barley

• Control the germination temperature of the barley

• Pasteurize stored malt

2. Mashing process control

• Prioritize brewing water quality and reduce acid addition

• If the brewing water pH is high, adjust the pH by adding lactic acid malt or using bio-acidification technology

• Minimize the mashing time

• Ensure the lauter wort is clear and transparent

3. Yeast strain selection

• Use low-acid yeast during fermentation

• Strengthen yeast management during production

• Avoid using yeast contaminated with wild yeast or foreign bacteria

• Avoid excessive temperature fluctuations in the fermentation tank

• Drain yeast promptly to prevent autolysis

4. Hygiene control

• Identify microbiological testing points and conduct regular sampling and inspections

• Clean all pipes and tanks according to regulations

• After each CIP cleaning, laboratory testing must be completed before use

• Remove and clean the filter weekly

• After each fermentation tank filling, clean the cold wort pipes and plate heat exchanger with a hot alkaline cycle

• Replace filter sheets and perform CIP cleaning

• Disinfect all nozzles

The Impact of Acidity on Beer Quality

Beer pH affects the following factors:

• Beer appearance

• Taste (hop bitterness)

• Beer foam stability

• Extraction potential

• Thermal coagulum formation

• Hop oil extraction

The above detailed analysis provides a more comprehensive understanding of the mechanisms of acid production in beer, the factors that influence it, and how to control it. This knowledge is crucial for optimizing the brewing process and controlling quality.