The Bitter Truth: Reassessing the Environmental Impact of Imported Hops in Brewing

Most UK craft breweries import their bittering hops. American CTZ, German Magnum or Herkules are standard entries on a lot of hop bills. The question of which bittering hop to use is usually answered by alpha acid percentage and price. Environmental impact rarely enters the calculation.

This article attempts to add a third variable: kg of CO2e per percentage point of alpha acid, across the three main markets supplying bittering hops to UK breweries. The data that exists is imprecise and the methodology requires some assumptions, but the conclusions are clear enough to be useful.

Why bittering hops are a separate decision from aroma hops

Aroma and dry-hop selections are driven by variety-specific characteristics: specific terpenes, biotransformation potential, oil composition. Bittering hops are a different purchase decision. Their primary function is isomerisation of alpha acids to produce bitterness. Beyond that, most breweries are buying on kilograms of alpha rather than kilograms of hop at a fixed alpha, because the bitterness contribution is what they are purchasing.

This matters for an environmental comparison because it allows you to normalise the CO2e impact by alpha acid content, not just by weight. A hop with a higher alpha acid percentage delivers more bitterness per kilogram, which means less physical product needs to be grown, processed and transported to achieve the same IBU target.

Decision factors in bittering hop selection

The practical factors that drive bittering hop choice are well understood:

• Alpha acid content: the primary driver. Most breweries buying at scale purchase on kg of alpha.

• Price: varies significantly by variety, supplier relationship, volume and storage capability.

• Hop age and storage: alpha acids degrade in poor storage conditions. The Hop Storage Index (HSI) quantifies this. A fresh UK Admiral at 15% alpha is a better bittering purchase than an older CTZ stored in suboptimal conditions.

• Co-humulone level: historically cited as a bitterness quality factor, but the evidence for a significant palate effect at typical craft IBU rates is weak, particularly in highly dry-hopped beers where the bitterness character is dominated by other variables.

The main bittering hop options by country

The most commonly referenced bittering hops from the three major supplying markets are:

• United States: CTZ (Columbus, Tomahawk, Zeus) are closely related varieties often sold together. Average alpha acid 15 to 17%, typically around 16%.

• Germany: Magnum (10 to 14% alpha, average around 12%) and Herkules (16 to 17.5%), which has largely replaced Magnum in high-alpha German production.

• United Kingdom: Admiral is the principal UK bittering variety, with alpha acid ranging from 12 to 18% depending on harvest and storage conditions, averaging around 15%.

It is worth noting that UK bittering hop development has been constrained by a genetic link between high alpha acid content and susceptibility to powdery mildew. New varieties are in development that target 14 to 18% alpha consistently, but the current position is that UK yields and consistency are generally below German and US equivalents.

CO2e per kg of hops by country of origin

Reliable CO2e figures per kilogram of hop production are scarce, but estimates from hop producers and researchers give a working picture. These are whole cone figures; the CO2e contribution of pelletising is assumed to be broadly equivalent across origins.

• UK hops: approximately 4.0 kg CO2e per kg (source: Carbon Cloud)

• German hops: approximately 3.2 kg CO2e per kg (source: Barth Haas)

• US hops: approximately 3.5 kg CO2e per kg (source: Yakima Chief Hops)

UK hops show the highest farm-level CO2e. This is likely attributable to lower yields from powdery mildew pressure and generally less advanced growing infrastructure compared to the large-scale Hallertau and Yakima operations. These are estimates, not audited figures, and should be treated as directional rather than definitive.

Adding transport: the full CO2e picture

Farm-level emissions are only part of the story. Bittering hops are transported in refrigerated containers, which use 15 to 35% more fuel than ambient equivalents. Assuming a standard 20-foot refrigerated container holding 10,000 kg of T90 pellets, and using route emissions data from Routescanner:

• Yakima (USA) to London: approximately 1,942 kg CO2e per container, or 0.19 kg CO2e per kg of hops. With a 25% reefer premium: 0.24 kg CO2e per kg transported.

• Germany to London: approximately 370 kg CO2e per container, or 0.037 kg CO2e per kg of hops. With reefer premium: 0.046 kg CO2e per kg transported.

• UK hops: domestic transport only, not calculated here.

Adding farm and transport emissions together gives total CO2e per kg: CTZ at approximately 3.75, Magnum at approximately 3.25, Herkules at approximately 3.25, and Admiral at approximately 4.0 with no transport addition.

CO2e per percentage point of alpha: the relevant comparison

Normalising by alpha acid content changes the picture. A brewery purchasing bittering hops is buying alpha acid, not weight. The CO2e cost per percentage point of alpha for the key varieties works out as follows: CTZ (16% avg alpha) at approximately 0.23 kg CO2e per alpha %, Magnum (12% avg alpha) at approximately 0.27 kg CO2e per alpha %, Herkules (15% avg alpha) at approximately 0.22 kg CO2e per alpha %, and Admiral (15% avg alpha) at approximately 0.27 kg CO2e per alpha %.

On this basis, US CTZ and German Herkules are broadly equivalent and represent the lowest CO2e per unit of bitterness purchased. UK Admiral and German Magnum are similar to each other and approximately 15 to 20% higher on this metric. The high farm CO2e of UK hops is partly offset by zero long-distance transport, but not enough to make Admiral the lowest-impact option at current yields.

What this means in practice

For breweries with sustainability targets, the implications are practical rather than ideological. Bittering hop decisions are typically made infrequently and in volume. Switching to a higher-alpha variety from the same origin can reduce the physical quantity purchased, which reduces both cost and CO2e simultaneously. Moving from Magnum to Herkules in the German supply chain, for example, requires roughly 20% less hop weight for the same IBU target.

For UK-sourced hops, the transport advantage is real but currently insufficient to offset the yield-related farm CO2e. This may change as new high-alpha UK varieties reach commercial production. It is worth maintaining a relationship with UK hop merchants such as Charles Faram to track variety development.

The data in this article will improve as more hop producers publish verified lifecycle assessments. What is clear now is that the environmental impact of bittering hops is quantifiable enough to factor into purchasing decisions, and that alpha acid content is the correct normalisation variable when comparing across geographies.

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