Lesson 2 - Wort Boiling Theory

Wort boiling should lead to a drop in wort pH of 0.3 to 0.5 pH units. A number of things contribute to this drop.

These are the:

• formation of melanoidins
• increased concentration of hop acids
• liberation of H⁺ ions when calcium and magnesium react with amino acids and peptides
• liberation of H⁺ ions when calcium and magnesium react with phosphates

The last of these is typically the most significant.

To achieve the required end of boil wort pH we need to start with the right pH. This is usually 5.5-5.8. The pH is affected by ions in or added to the water and the mashing and wort separation process used.

By the end of wort boiling, the pH should be 5.0-5.3. This is a good compromise to achieve the requirements of wort boiling.

Calcium ions react with phosphates displacing the H⁺ ions and calcium phosphate is precipitated.

At least half the calcium present in wort may be precipitated by the end of the boil. As a result, wort with a starting concentration of 100 mg/L of calcium, may have only 40 mg/L of calcium when cast into a fermentation vessel. Calcium sulphate or chloride is sometimes added to encourage a reduction in pH during the boil.

Calcium also reacts with oxalic acid released from the malt during the mashing process, forming calcium oxalate (CaC₂O₄). If the calcium oxalate is not removed in the boil, there is a risk that it will form a scale on fermentation vessels known as beer stone. Crystals of calcium oxalate can also cause beer gushing. This is when the crystals form nucleation sites for CO₂ bubbles in the beer, leading to it over foaming when the package is opened.

It is also possible to reduce the pH directly by adding acids, such as phosphoric or lactic acid. Phosphoric acid might be used in some high gravity or high adjunct worts, which can suffer from a deficiency of phosphate. Lactic acid or sour wort is thought by some brewers to produce a smoother tasting beer than those acidified with mineral acids or high levels of calcium or magnesium. Sour wort is produced by fermenting unhopped wort using specific strains of Lactobacillus.

Achieving the right pH throughout the boil is important for many reasons. For example, it:

• Improves protein coagulation.
• Improves diacetyl reduction during fermentation.
• Encourages yeast growth.
• Helps increase fermentation rate.
• Inhibits the growth of spoilage microorganisms.
• Reduces colour formation.
• Helps achieve the correct beer pH.

The following article gives more information on the importance and control of pH in brewing – “The Role of pH in Brewing” by Tim O’Rourke, which can be found in the IBD Library.