Lesson 10 - Hops Final SAQ

**A brewer has complained to you that the hop utilisation at the brewery is much lower than expected. What questions would you ask the brewer, to help them trouble shoot their hop utilisation problems? Provide recommendations of what they should do.

Response:

You could ask the brewer about various aspects of the brewing process to help problem solve the utilisation issue. You could ask about:

-       The type of hop variety/hop products they are using.

-       Their wort kettle boiling conditions.

-       Their downstream processing conditions.

-       The type of product they are brewing.

A starting point would be to find out what hop variety and hop product they are using, to see if it is fit for purpose.

What α-acid do the hops have? If the α-acid is very low, then it would require many more hops to achieve the target. Excessive hop loading can affect utilisation.

What hop products are they using? Whole hops have a low utilisation, whereas pre-isomerised hops have a much higher utilisation and are more efficient. There is also the option of post-fermentation bittering with much higher utilisations.

How old the hops they are using? α-Acid levels decrease with oxygenation of hops, but other bittering substances increase, but not as classic α-acids bitterness.

What pH is the wort at boil? Increasing the pH of the wort during wort boiling increases the hop utilisation. Substances in the wort that promote acidity, or generate buffering capacity, can influence pH e.g. divalent ions like magnesium or calcium. However, divalent ions can also help catalyse the isomerisation process, so there needs to be a balance.

What is the boil duration? The longer the wort is boiled with hops added, the more the hops will be utilised, up to a maximum point of around four hours.

What is the wort gravity? High gravity worts result in lower hop utilisation. Is the product a high alcohol product, thus needing higher gravity? In which case, the brewer will have to look at alternative options for optimising utilisation. However, if it is a standard alcohol and they are not capacity constrained, then dropping the gravity would be beneficial.

What is the temperature and pressure of the boil? The higher the temperature of the wort, the more effective the isomerisation (isomerisation drops significantly below 80^°C). By boiling at a higher pressure, you can increase the utilisation within a smaller period of time (i.e. it will take 4 hours to fully utilise hops at 100^°C, but only 20 mins at 120^°C). By increasing the wort boiling pressure, you increase the boiling temperature. If the brewery is at a higher altitude, then the boiling temperature may be sub-optimal. You could increase the pressure of the boil, or used pre-isomerised hop products if you have any concerns, but it is likely that the boiling temperature will only drop to a minimum of around 95°C. This will still result in effective isomerisation.

How effective is the boil? A traditional ‘rolling boil’, or other methods of achieving good physical agitation, is useful for isomerisation.

After the brewhouse, the key questions would be:

Is there any fobbing in the process (from wort kettle onwards)? Is there any foam formation? This foam may be present in the wort kettle due to excessive boiling. Excessive foam (fobbing) during fermentation can lead to loss of α-acids and iso-α-acids.

What type of fermentation vessel is being using? Cylindroconical fermenters result in less loss of bittering substances, compared to open fermenters. This is mainly due to better circulation of the fermenting medium, resulting in better hop compound solubility and less fobbing.

It should also be noted that bittering substances can be lost due to adsorption to yeast cells and being removed by filters, so this would need to be factored in and would contribute to overall bitterness loss in the brewing process.