Hops A-Z; U is for Utilisation

It's one thing to have heaps of sticky lupulin to cram into a beer. It's something else to get the right amount of bitterness in there - and keep it there.

The isomerisation of alpha-acids we've talked about earlier isn't a straightforward equation. In fact, it's a fairly inefficient process. If a brewer achieved 50% utilisation - that is, 50% of the alpha-acids present in the hops were isomerised and made present in the beer - that would be outstanding. A utilisation rate of 25-40% is more usual.

There are a whole number of factors that a brewer has to consider when trying to optimise the utilisation rate:

Type of hop product used?
- pellets and shredded cones utilise better than whole flowers

Rate of hopping
- More hops lead to less utilisation

Length of boil
- a vigorous boil for 60 mins at 100c helps disperse the alpha better, but eventually the longer the boil, the more the alpha-acids degrade

Nature of the wort
- higher gravity and lower pH worts reduce utilisation

Fermentation conditions
- a flocculant yeast reduces utilisation as it drags iso-alphas from the beer

Maturation and filtration
- the time and temperature of maturation, twinned with the level of filtration, will affect the level of iso-alphas surviving in the finished beer.

What fascinates me about utilisation is the coming-together of science and art. There are a whole host of tables that analyse the utilisation rate in terms of bitterness units, boil times and original gravity. Knowing the utilisation rate and the alpha of the hops used, you can calculate the bitterness of the beer. Knowing the bitterness level you want, you can do the maths backward to understand the utilisation rate needed and therefore the boil time required for the beer's gravity.

But there's a touchy-feely side to all of this that I didn't fully appreciate until I worked with commercial brewers. How the equation is changed by the shape of the copper, the combination of hops, fluctuations in the crop, tired yeasts, which side of bed the brewer got out of that morning...

If it was all about the maths, utilisation would be easy. Brewing would be easy. Thankfully, there's enough organic stuff in the equation to make the process far from predictable. As macro-brewed, numbers-driven beer proves all too often, exacting maths can lead to dependably boring beer.