Lesson 3 - Wort Boiling Theory SAQ

*Give short answers to the following:

a)    What is the optimum pH at the end of wort boiling? Why is ensuring that the pH is correct during the boil important?

b)    Your start of boil gravity is 9.7°P and end of boil gravity is 10.6°P, what is your percentage evaporation? Do you think this is acceptable? Why?

c)    When do kettle finings need to be optimised and what two parameters do we need to balance when optimising them?

d)    How can you improve the utilisation of T90 hops during wort boiling?

e)    The wort DMS at the end of wort boiling is 220 μg/L. How is this likely to affect the beer, and what action would you take for future brews?

Response:

a)    The optimum pH at the end of wort boiling is 5.0-5.3. The correct pH during wort boiling is important because it:

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

However, hop utilisation is not optimal in this pH range.

b)    We can calculate evaporation using this equation:

So for our figures the percentage evaporation is:

8.5% evaporation is within an acceptable range of 4-10%. However, to optimise quality, cost and environmental impact, there is scope for reduction. The minimum evaporation level that achieves the objectives of boiling is optimum.

c)    Kettle finings need to be optimised regularly. They must be optimised immediately if any process parameters are changed, if there are any changes in raw materials or if changes in wort clarity or levels of cold break are evident. Optimisation requires achieving the correct balance of wort clarity and compactness of the sediment. We need the wort to be as clear as possible and the sediment in the Imhoff cone to be as compact as possible. 

d)    To increase hop utilisation we can:

• Increase wort pH.
• Reduce trub volume.
• Increase boil time.
• Reduce wort gravity.
• Increase the boil temperature.
• Change to a hop variety with a higher α-acid level.
• Reduce any fobbing/foaming during wort boiling.
• Increase boil vigour.

Some of the options are less viable than others as they negatively affect other boiling objectives and beer flavour.

e)    DMS has a flavour threshold of around 30-50 μg/L. Unless it is a desirable flavour in the beer we are trying to produce, it is recommended that the level of DMS at the end of wort boiling is below 50 μg/L. At 220 μg/L the beer is likely to have a strong DMS aroma which is seldom desirable. Ideally, we should blend this brew with one lower in DMS. We also need to take steps to reduce DMS in future brews.

The best ways of reducing the DMS levels involve using:

• Malt with low SMM levels.
• Sufficient heat added to convert SMM to DMS.
• A wort boiling system with effective evaporation and removal of volatiles to remove the DMS formed.
• A short residence time in the wort clarification vessel, to prevent more DMS forming from SMM.
• Rapid wort cooling, (reducing the time that the wort is hot).
• Wort stripping after the wort clarification vessel, to remove DMS.