Lesson 5 - Hop Chemistry SAQ

** You are the head brewer for a new start-up craft brewery. You have not been able to secure any hop contracts yet and thus only have access to small amounts of a selection of different standard hops. You need to source hops for your flagship beer, which has a perceived bitterness target of 25 IBU. The brewery is still being designed, so you can make changes to the process and equipment if required.

a)    Detail what type of hop variety you would select (and why). What would you do to increase the hop utilisation to maximise the small amount of hops you have managed to source?

b)   Consumer testing has shown that they would like the beer to have more hop aroma. What changes would you make to your hop choice and/or process, to achieve the desired hop aroma, as well as bitterness target?

Response:

a)    Firstly, the hop variety should be a ‘bittering’ hop variety, with a high α-acid content. The question states that the brewer will only have access to small amounts of hops, and so it is important to choose a hop that can be added in smaller amounts to achieve a desired bitterness target.

Looking beyond the α-acid content, the brewer could consider choosing a variety with a high cohumulone level, in addition to the α-acid, to help maximise the perceived bitterness. To increase the hop utilisation, the brewer has been told that they can make changes to the brewery, so the options that the brewer can consider are as follows:

• pH – target a higher wort pH as possible.
• Boil time – extend the wort boiling time (or at least ensure that all hops are added at the start of the boil to maximise contact time).
• Temperature/pressure – increase the pressure in the wort kettle (design) to increase the temperature of the boil above the atmospheric boiling point.
• Wort kettle/boiling system – select a wort kettle that improves circulation, with physical agitation as a primary goal, and look at designs which increase pressure and temperature as a secondary goal.
• Wort gravity – brew at standard gravity and not high gravity.
• Hop products – although not covered in detail here, mentioning pre-isomerised hops is the key point.
• Trub reduction – by reducing trub, you will reduce the loss of bittering substances (including polyphenols).
• Quantity of hops added – selecting the right hop variety with a high α-acid level will ensure that addition rates are kept lower, which will in turn increase utilisation.
• Hop age – use fresh hops and not old hops.
• Foaming – reduce foaming throughout the brewing process to reduce the loss of bittering substances that are removed in the foam or fob.
• Yeast – try to limit yeast growth to reduce the amount of yeast cells available to adsorb bittering compounds.
• Filtration – avoid excessive filtration to reduce bittering substance loss, or at least reduce the amount of filtration (such as sterile filtration).
• Fermenter type – use cylindroconical fermenters, ideally over open fermenters, due to better circulation of the fermenting medium.   This results in better hop solubility and less fobbing.

(It should be noted that some of these practices may increase hop utilisation but may be detrimental to other aspects of beer quality.)

b)   The consumer feedback in the question did not state what type of hop aroma was desired, and only that hop aroma was required. It would therefore be possible to keep the current hop variety as the key is to ensure that the perceived bitterness target is achieved. By choosing a more classic ‘aroma’ variety, it is likely that the variety will have a lower α-acid and hence require more hops to achieve the bitterness target. If possible, the brewer could select a hop variety that has high α-acid and good aroma characteristics (such as Citra).

The main options available for increasing hop aroma using standard hops (i.e. no specialist hop products) are by either adding hops later on in the boil or whirlpool, or by dry hopping. Dry hopping does add perceived bitterness, mainly due to compounds such as humulinone. Since humulinone bitterness is only 66% as intense as iso-α-acid, it would require significantly more hops to achieve the perceived bitterness required. As humulinone is an oxidised α-acid, it is not readily known what percentage of the analysed α-acid may be transformed. It is hence difficult to quantify how many more hops to add in order to achieve the bitterness target; it would likely be much more than an additional 34%.

The only realistic option is adding the hops later on in the boil, but still early enough that the isomerisation percentage is high enough to achieve the bitterness without the need to significantly add more hops.