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New hop varieties to combat climate stress

Where do the many new hop varieties come from? How has hop breeding changed in the last decades? Why is the crop yield no longer automatically the number one breeding objective? The two hop experts Dr. Adrian Forster and Dr. Florian Schüll from Hopfenverwertungsgenossenschaft HVG e.G. in Wolnzach, Germany, explain what hop breeding is all about and why brewers should be interested in it.

Hop breeding garden with young hop plants on climbing aids Tomorrow's hop varieties sprout in the hop-garden in Hüll (Picture: BRAUWELT)

Hop varieties resistant to disease and climate


Currently about 300 hop varieties are registered, and in the last 20 years the number of new hop varieties worldwide has continued to grow. In Germany alone about 30 varieties are commercially grown, in the 1950s there were only four varieties. The hop cultivation area is thus spread over more and more varieties.

There are also many new breeds of malting barley, but more at the expense of older varieties. In hops, on the other hand, new breeds supplement the range of varieties. Even the old country varieties Hallertauer Mittelfrüher, Hersbrucker, Spalter and Tettnanger are still in demand worldwide. The number of available varieties is constantly increasing - it's easy for brewers to lose track. It is particularly worthwhile for brewers to closely observe the development of the new hop varieties.


Crossbreeding of wild and cultivated plants

 

Up to now, hop varieties have been developed almost exclusively by crossing female cultivated plants with male plant material, which often originates from crosses between wild and cultivated plants [1, p. 120]. A look at DNA can provide insights into, for example, disease resistance and facilitate more effective crossbreeding. However, breeding is still dependent on testing the properties of countless plants. Success therefore depends on the diligence and intuition of the breeder. This also requires a good portion of luck.

Peronospora trap in the hop gardenA peronospora trap in the hop garden, because effective resistance to this fungal disease has not yet been realised (Picture: BRAUWELT)

Early breeding objectives had wilt resistance in mind


As early as the 1910s, the first Brewers Gold and Northern Brewer varieties were developed in England with the declared aim of higher alpha acid values. The Northern Brewer also proved to be resistant to wilt.

The fungal disease peronospora already dramatically damaged the Hallertau harvest in the 1920s. In addition, the main Hallertauer Mittelfrüher variety increasingly proved to be highly susceptible to wilt. Breeding at the Hop Research Centre in Hüll, beginning in the 1950s, was therefore to produce new varieties with significantly improved tolerances or even resistance to wilt and peronospora.

A glance at the list of currently relevant hop varieties also includes resistance and tolerance properties against wilt, peronospora and mildew [1, p. 137; 2]. Only three out of 40 varieties are listed as "good" for these three diseases, but they still need to be treated with plant protection products, albeit much more moderately. Effective resistance to some, and certainly not all, diseases has not yet been achieved.


Strong increase in newly registered breeds

 

The development of newly approved hop varieties by the Society for Hop Research in Hüll began in 1951, and the number of applications has risen sharply in the last ten years.
This increase becomes even more apparent when imported US breeds such as Cascade, Amarillo and Comet are added. It is also worth noting that an additional five varieties were registered in Germany by private breeders in 2019. These varieties are completed by the old landraces which are still in demand.

Registrations of breeding varieties in Europe (excluding Germany) have also risen sharply since 1995 - from six registrations in 1995-2000 to 15 registrations in 2016-2019 [3, 4].

Several reasons are responsible for this rapid increase in breeding.

Three Craft Beer glasses on a table, the middle glass is filled with beer, the two outer glasses are filled with hop conesCraft brewers use considerably more hops than "classic" breweries, and they experiment with many different hop varieties (Picture: NürnbergMesse, Heiko Stahl)

Craft beer wave triggers hop boom


The Craft Beer wave that started in the USA has now reached the whole world. Hops - degraded to a less important raw material for most of the world's beer production - have been completely re-established by craft brewers as an essential means of characterising and differentiating their beers. They have discovered hops as a mediator of aromas which do not have to be typically hoppy.

This development has given an enormous boost to breeding and led to a flood of applications. The varieties also known as flavour hops (= hops with a special, unique aroma) are often used for hop stopping (= hopping in cold areas). Of 20 of the varieties registered in Germany and the USA in the last seven years, 18 belong to the category of specially fruity flavour hops.


More and more private breeders


Until the 1980s, the breeding of hop varieties was almost exclusively carried out by organisations (e.g. universities, state institutes) with the support of public authorities, mainly in Germany, England, the Czech Republic, Slovenia and the USA. These still play a major role today in countries such as Germany, the Czech Republic or Slovenia.

In countries such as the USA, England and Australia private breeders, mostly hop growers and trading houses, now dominate. Recently, however, private breeders have also become active in Germany.


New hop varieties are often legally protected


Many new varieties are now legally protected and are only available for royalties, as the aim is to make money from breeding. It is obvious that private breeders are more aggressive in marketing their varieties than public breeders. A positive side effect is that increasing competition among breeders will lead to increased efforts with - hopefully - better chances of success. However, it is becoming increasingly difficult for brewers to keep an overview.

Close-up of hop blossomsHop plants flower in July (Picture: BRAUWELT)

Agronomic breeding objectives


What are the main objectives of current new breeds? Typical agronomic objectives such as yield (kg/ha), alpha yield (kg α/ha) at least for bitter hops as well as good cultivation properties remain valid. For the brewer, characteristics such as quantitative and qualitative bitter and aroma potential play a major role.

In the case of flavour hops, the hype for new flavours is added, although it can also be more short-lived. There are now so many different varieties available in this category that cannibalisation is inevitable.


Restrictive plant protection rules increase pressure on breeders

 

In the meantime, however, two serious problems have come to the fore. Agriculture is generally confronted with more restrictive regulations on fertilisation and plant protection and will have to deal with these ecological restrictions demanded by society in the future. The authorisation of plant protection products is subject to critical examination of ecological aspects.

The number of plant protection products authorised for hop growing is already steadily decreasing. New products are often inferior to older ones in terms of their effectiveness, but are more environmentally friendly.

This increases the pressure to develop varieties with significantly improved resistance/tolerance to diseases and pests such as wilt, powdery mildew, peronospora, hop aphids and red spiderwort. However, these requirements mean that higher yield performance no longer has to be the dominant breeding objective.


Climate-tolerant varieties urgently sought

 

During the vegetation months of May to September, climate change has caused a temperature increase of 2°C in the Hallertau over the last ten years compared to the long-term average of 1961-1990. This is coupled with lower precipitation and a significant increase in the critical heat period for hops (> 30 °C).

Hop varieties react differently to this climate stress [5]. European aroma varieties are particularly sensitive, whereas US varieties are more tolerant. Since American hops have been crossed into many German bitter and flavour varieties, they are less sensitive to heat than traditional European aroma hops.

In our opinion, disease and climate tolerance should be the top priority in variety breeding. A variety with 22 percent alpha acids and a high alpha yield may be attractive at first sight. However, if it is inferior to a variety with a somewhat weaker alpha yield in terms of climate and diseases, it will not have any raison d'être in the long term. Under similar aspects, older aroma varieties that are less able to cope with climate pressure are to be seen.

A board with botanical drawings of hops is leaning between two taps and a brewing kettleHops have such a decisive function in beer production that brewers should also be interested in hop breeding (Picture: BRAUWELT)

Why should brewers observe hop breeding?


Climate change and disease pressure play a dominant role in hop-growing. Varieties which no longer meet the changed requirements will lose in importance. In particular, it is to be hoped that the increasingly broad-based breeding with correspondingly disease- and climate-resistant varieties will find adequate answers.

Brewers should follow this development closely and not shy away from trials. All those involved must expect setbacks. It is questionable whether all varieties grown today will still be available in 20 years' time. Older varieties will change in quality due to climate change and will probably be considerably more expensive to grow.

It is already apparent today that the average alpha content of older varieties decreases with warmer and drier summers. The brewer is more or less relieved of the decision on new barley varieties by the trade and maltsters. He often does not even notice the coming and going of varieties. When it comes to hops as a raw material, however, he should definitely follow what is happening so that he can adapt to new developments in good time.


Literature

  1. Biendl, M., Engelhard, B., Forster, A., Gahr, A., Lutz, A., Mitter, W., Schmidt, R. und Schönberger, C.: Hopfen – Vom Anbau bis zum Bier; Fachverlag Hans Carl, 2012.
  2. Pocket Guide 2016 – German Hop Growers Association.
  3. Data of the Society for Hop Research Hüll of October 2019
  4. https://cpvoextranet.cpvo.europa.eu/mypvr/#!/en/publicsearch
  5. Forster, A. und Schüll, F.: „Der Einfluss des Klimawandels auf den Hopfen“, BRAUWELT Nr. 36, 2019, S. 1020-1024.