Lesson 6 - Wort Boiling Final SAQ

***With reference to process and technology, explain how you can achieve the objectives of boiling without boiling the wort.

Response:

We should be very familiar with the objectives of boiling by now. We can take them one by one and explain how we can achieve them without boiling. 

1. Inactivation of malt enzymes

We don’t need to boil wort to denature enzymes. Even the most heat stable is denatured below 80°C. It is important to understand that denaturation is not an instantaneous process so simply flash pasteurising them for a few seconds at 80°C is not likely to inactivate them all. Holding wort for a few minutes close to 100°C should have the desired effect. Checking for the activity of limit dextrinase (which has a more heat stable bound form) would be wise before we decide this approach has been successful. If we heat the wort in a kettle, we should ensure that the wort is continuously mixed as the heat is applied to ensure it is evenly distributed. A more practical way might be to pump the wort through a heat exchanger with a section of holding tube after, where the temperature is maintained.

2. Destruction of vegetative microbial cells:

A full boil is not necessary for killing vegetative microbial cells. However, the same principle of this not being achievable instantaneously applies. We could pasteurise the wort which involves heating it to a set temperature for a set period. It is possible to calculate the number of pasteurisation units required if we know the:

• Wort viscosity
• Wort pH
• Wort microbial load
• Types of organism present

The few minutes at close to 100°C we indicated above should provide more than enough pasteurisation units to achieve the objective.

3. Development of flavour and colour.

Since it occurs in a standard boil (100°C), we know that the Maillard reaction occurs at temperatures below its optimum range of 140-160°C. The lower the temperature the slower the rate. Irrespective of the wort temperature, thermal energy drives the reaction so if we are not actively heating the wort the reaction will be slower. Holding the wort at just below boiling for an extended period should produce similar colour and flavour to a full boil. Another option is to increase the level of the reactants (FAN and reducing sugars) and use a slightly increased period at the raised temperature. If the flavour we require comes from caramelisation, we are likely to struggle because caramelisation probably won’t get going below 100°C or occur in a sensible timeframe. Many commercially produced colourings and flavourings are available that we could use to add any colours or flavours we were not able to form at below 100°C. Hop aroma and flavour compounds should dissolve as they do in the boil, as long as there is sufficient agitation to extract them from the hop products used. An increasingly large range of hop flavour products is also available and we can use them to approximate the flavour achieved by boiling hops.

4. Extraction and isomerisation of hop compounds:

Isomerisation doesn’t occur at a reasonable rate below boiling temperature. Fortunately, pre-isomerised hop products are available and we can achieve target bitterness levels by dosing these in at any stage of the process after wort separation.

5. Formation and precipitation of protein/polyphenol complexes:

We don’t need to physically boil wort to achieve this, however we do need to get close. Holding the wort at just below 100°C while agitating and sparging with gas or steam can cause protein coagulation and provide the interface required for proteins and polyphenols to interact. Gallotannins/silica sols and PVPP (added separately!) can be used to assist in removing proteins and polyphenols respectively.

6. Removal of unwanted volatile flavour compounds.

To remove volatiles, we need to heat the wort to the point where the volatiles boil and to strip them from the wort. With DMS we need to form it from SMM first. That requires heat. Holding the wort just below 100°C and then stripping it with steam or gas will achieve this. We can heat and strip in the kettle or heat in the kettle and strip in a wort stripper.

7. Acidification of the wort:

This is an easy one! We add acid. This is a better option than adding calcium or magnesium (unless there is a deficiency in the wort) because the effect on flavour is less. Lactic or phosphoric acid are the best option as they affect flavour less than sulphuric and hydrochloric.

8. Activation of foam stabilising proteins:

Temperatures below boiling are sufficient to achieve this although the wort may need to be held at these temperatures for longer than in a standard boil. Protein Z is thought to be glycated in the Maillard reaction and this is likely to require more thermal load than the conformational changes to the proteins. If we are not able to achieve the desired foam stability, we could add foam stabilising process aids later in the process like reduced hop extracts or propylene glycol alginate.

This all paints a positive picture of omitting a wort boil. While it’s great as a theoretical exercise, we should bear in mind that we don’t fully understand everything a boil does for us. Our boil-free beer may not taste very nice or have the other attributes we associate with a great beer. We certainly wouldn’t be able to match the flavour a of conventionally brewed beer using the above approach.