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How to calculate a hop aroma addition

It’s not rocket science that hop aroma additions are usually done at the end of wort boiling (a few minutes before end of boil). To increase the aroma utilization, some brewers dose their aroma hops even after the boil, into the whirlpool. How to dry hop – that’s another big topic which won’t be discussed this time – we want to focus on calculations. The calculation for late hop dosages in the brewhouse is actually also applicable for dry hopping.

Hop oils are (mainly) responsible for the hoppy aroma in beer. These hop oils are present in their free form and also are glycosidically bound to sugar compounds in hops. There was a lot of research going on in the last few years about glycosidically bound hop oils. Studies showed that these compounds may contribute quite a bit of hoppy aroma – or at least they increase the concentration of certain (free) hop oil components in the final beer. In many cases, the bound hop oils are set free during fermentation by yeast activity. However, it’s very difficult to analyze hop oils present in very low concentrations and to categorize the impact of this compounds. That’s why these glycosidically bound oils aren’t (yet) considered in calculations for hop aroma additions.

Currently, there are a few different methods for calculations: one can use the total oil content of hops (or hop products), use a so-called “character impact compound” like Linalool, or just dose according to the amount of hops (cones or pellets).

In many breweries, the addition is still calculated on an alpha acid basis according to one of these two examples:

  • Example 1: „60% of the total alpha acids is dosed at the beginning of the boil for bitterness, 40% is dosed at the end of boil for aroma”
    or
  • Example 2: „The aroma addition at the end of boil consists of 4 gram alpha acid per hl wort“

Alpha acid is for sure THE important bitter component for a brewer, but alpha doesn’t contribute to a hoppy aroma in your beer at all. This tells us that alpha acid is probably not the best way to calculate your hop aroma addition. There is indeed a certain correlation between alpha acid and oil concentration in hops which means: depending on crop year, if you have a high alpha acid content, also the oil content might be higher than average and the other way round. One example: in year X, the alpha acid content is 5%, the oil content is 1 ml/100 gr hops. In year X+1, the alpha is 4.5%, the oil 0.9 ml/100 gr – everything is alright! Even if you calculated your dosage based on alpha, the amount of oil dosed to your beer is the same. But what if in year X+2 the alpha acid content is 4% and the oil content is 1.2 ml/100 gr? It means in year X+2, you dose 50% more oil than in years X and X+1! This is probably not a big issue for hop enthusiasts, but for sure for a brewer who insists on a more or less consistent beer aroma. Particularly in years with weather extremes – which we face more and more – we can see bigger discrepancies between alpha acid and/or oil contents or their ratio, respectively.

The addition of always the same amount of hops at the end of the boil or into the whirlpool might involve the same risk: the average oil content of a hop variety is e.g. 1.2 ml/100 gr, but also values of 0.8 ml or 1.5 ml are possible. This means the oil dosed into your beer can be double of only half the amount from one year to the next.

Maybe this won’t cause a hop aroma in your beer which is double (or half) as intense, but even a not so experienced beer drinker will easily detect the difference.

So, only two possibilities remain: a dosage based on the total oil content, or a calculation according to the linalool content of hops. The latter one also includes some disadvantages: linalool was repeatedly described to be the (or one of the) character impact compound(s) of hops where it is present in quite high concentrations. Also, it’s comparably easy to detect in hops (and beer) by gas chromatography. In the traditional fine aroma hop varieties (like Saazer, Halletauer Mittelfrüh, Tettnanger, Hersbrucker…), linalool is one of the most prominent aroma compounds found in beer using these varieties. But it’s not the only one, and especially with the new “flavour hops”, it’s not really the most important one. How should one explain why these flavour hops all provide very different aroma profiles in raw hops as well as in beer (in most cases non-“linalool-like” floral and citrus)? Additionally, the linalool concentration within the total oil content of hops varies a bit, resulting in different amounts of hop oil in your beer leading to differing aroma intensities and qualities. Last but not least, the gas chromatographic (GC) analysis for the concentration of linalool isn’t cheap…

This brings us to the favoured method of calculation: the total hop oil content. This is the only way to ensure that you always dose the same amount of hop oil into your beer. Of course, you need to know the oil content of your hops. The volumetric hop oil analysis is much cheaper than the GC analysis for e.g. linalool. The overall composition of a hop oil may – as already mentioned above – naturally vary a bit from crop to crop and cause again slight changes in quality and intensity of hop aroma. Nevertheless, from our point of view, this is the easiest and by now the most accurate way of calculation for a consistent hop aroma in beer.

Finally, let’s look at the amount of hops or hop oil to be dosed into your beer. This depends very much on:

  • Hop variety (1 ml oil of variety A can be much more intense than 1 ml oil of variety B)
  • Beer style (sounds self-explanatory)
  • Alcohol content (influences the perception of hop aroma)
  • Degree of Fermentation (influences mainly the taste)
  • Character of the beer itself (like malt aromas, yeast by-products…)
  • Desired intensity of hop aroma
  • Desired quality of hop aroma

Attention should be paid to the fact that double the amount of hops doesn’t give you double the aroma intensity (keywords: saturation and synergistic effects). If the oil dosage and hop aroma intensity increases, the quality of the aroma will also change: again, the interaction of single aroma compounds play a big role (synergistic effects!) Also, aroma substances are perceivable only at a certain concentration in beer because it reaches its flavour threshold. Only at high levels could it “push through” against other aromas.

Many craft brewers still dose their hops according to a certain amount, e.g. 500 gr pellets per hl beer. That’s easy to do since you don’t need any analytical tools, and as long as your goal is not for 100% consistency of hop aroma in your beer, it’s not a problem at all.

Maybe it’s even a positive (wanted?) effect that the leading ingredient (aroma-wise) in many beers – HOPS – is a natural product can’t be standardized completely and provides year to year crop fluctuations – like wine always did…

500 gr of hops per hl beer is only a rough benchmark as an average hop dosage in US craft beers (sometimes even indicated with 700 gr/hl, this figure is difficult to define).

Depending on what you want (and the beer style allows), this could also be only 20 gr, or sometimes an incredible 2000 gr per hl! There really are no limits, as long as your brewing equipment allows you to do so! For an “oil” dosage, this would be something between 0.2 ml and 20 ml oil per hl beer.

To conclude: it’s quite easy to explain a suitable way for calculations, however, we never can predict the aroma in the final beer which makes it even more interesting and challenging!

Since the aroma addition, to a certain extent, also contributes to the bitterness, one should always start with the calculations for the hop aroma to find out how much hops is needed to reach the desired bitterness in the final beer. For example, you know how much alpha acids you dose with your aroma addition (end of boil or whirlpool). The utilization rates at the end of boil or in the whirlpool are usually in the range of 5 to 20%, depending on brewing equipment, heat holding times, gravity, base beer, total amount of hops…. This tells you about the bitter contribution of your aroma addition. If you reduce your bitter addition at the beginning of boil (plus any addition during boil) by this contribution from the aroma addition, you will easily get the desired bitterness in the final beer. Also, dry hopping can contribute to beer bitterness. There is no more isomerization from alpha-acids to iso-alpha acids, at least a small amount of the (in beer poorly soluble) alpha-acids might go into solution. The bitterness intensity of alpha-acids is quite low, but if lots of hops are added in the cold part of the brewery, this could definitely influence your beer bitterness.

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