Lesson 6 - Wort Clarification, Cooling and Oxygenation Final SAQ

***Explain a typical modern lager wort clarification and cooling system. Compare it to a system that could be better used to make traditional ales.

Response:

A typical modern lager system can include the following:

• Whirlpool.
• Centrifuge.
• Plate heat exchanger.
• Oxygen dosing for high gravity on the cold side of the plate heat exchanger.

A typical traditional ale system could include the following: 

• Hop back.
• Coolship.
• Wort dilution.

We are concerned with the following parameters:

1. The use of different hops, and thus different clarification needs.
2. The degree of trub removal (wort clarity).
3. The temperature of cooling (fermentation temperature).
4. The levels of aeration/oxygenation.
5. The use of wort dilution.
6. The effects on colour and flavour formation.
7. The possible impacts on the yeast types (lager versus ale).

Modern lager brewing would typically aim to achieve rapid clarification with bright, clear wort. The whirlpool is the method of choice for many modern breweries, as it has a relatively low total cost of ownership (TCO) yet achieves  efficiency and quality requirements. Centrifuges can also be used (in place of, or in addition to) but at a higher TCO, due to the increased energy and maintenance requirements.

Ales typically have higher fermentation temperatures than lagers and thus  are also cooled and pitched at higher temperatures. These temperatures are typically:

Ale wort collection: 15-22^°C

Lager wort collection: 6-12^°C

We therefore require a lower cooling load to achieve cooling.  Some smaller breweries can even use the local municipal water at an ambient temperature of 12-15^°C to achieve the required cooling.

For a modern lager, probably at high gravity, the main issue we would need to re-evaluate is wort aeration. The higher the gravity, the higher the amount of oxygen needed. At high gravity we also need to use pure oxygen to achieve the higher requirements of dissolved oxygen that come with increased yeast and lower solubilities.

Ales could more often dilute wort before, during or after wort has been cooled into the fermenter. The cooling requirements will change as the volume of liquid to be cooled will change, depending on the addition point of the dilution water. If we use dilution water dosed in before the wort cooler, then the cooler will need to be bigger to accommodate the extra volume, ensuring that we do not extend cooling times. This could however be an option for smaller (and slower) traditional breweries, who are not as concerned with cycle times as commercial breweries.

The wort clarity (amount of trub carried over), the aeration (air versus oxygen and the dosing point), and possible wort dilution, will affect the wort and therefore the performance of the yeast. Traditional ale yeast would be top fermenting, whilst lager yeasts are bottom fermenting. There is typically less of a concern for ale beer clarity, as they are also often much darker in colour than lagers.