Hop Aroma Science: Nitrogen's Influence Explored

Nitrogen is an essential plant nutrient for hops, and its application and timing are crucial for maximising hop yields. However, the impact of nitrogen on hop aroma is a complex topic that requires further exploration. While some sources suggest that nitrogen fertilisation can influence the presence of certain compounds in hops, such as bitter acids and prenylflavonoids, the relationship between nitrogen and hop aroma is not explicitly mentioned.

A study by Czubacka et al. (2024) investigated the effect of reduced nitrogen fertilisation on the activity of genes involved in the production of bitter acids and xanthohumol in two hop cultivars. The results showed that a reduction in the nitrogen dose by 25-30% did not significantly affect gene expression or the content of secondary metabolites. However, the study did not specifically address the impact on hop aroma.

In brewing, the addition of hops during the dry hopping process can influence the bitterness of a beer, and high nitrogen content in hop sediments has been found to affect the composting process. While these findings provide insights into the role of nitrogen in hop cultivation and brewing, more research is needed to establish a direct connection between nitrogen and hop aroma.

Nitrogen is an essential plant nutrient for hops

Nitrogen is a vital component of plant growth, and in the case of hops, it is particularly important for cone production. Hops are unique in that they accumulate large amounts of nitrogen in their biomass, which is then stored in the leaves and translocated to the cones. This process of nitrogen accumulation occurs rapidly during the month of June and is typically complete by early July. Therefore, it is recommended that hop growers apply nitrogen fertiliser by mid-June to ensure adequate nitrogen availability during this critical growth stage.

The amount of nitrogen required by hops can vary depending on factors such as cultivar, age, and yield. On average, hops require between 100 and 150 lb N/a, with higher-yielding cultivars needing more nitrogen. Proper nitrogen application rates are essential to optimise cone production and ensure the economic viability of hop farming.

In addition to commercial nitrogen fertiliser, hop growers can also utilise other sources of nitrogen to meet the crop's needs. These include soil organic matter, manure, cover crops, and returned hop vines. When using these alternative sources, it is important to adjust the nitrogen fertiliser rate accordingly to avoid over-application.

The complex behaviour of nitrogen in the soil can make it challenging to develop accurate soil tests for predicting nitrogen fertilisation requirements. As a result, growers often rely on nitrogen budgets, which estimate the amount of nitrogen needed by the crop based on plant uptake and other factors.

Overall, nitrogen plays a critical role in hop production, and its availability directly impacts the yield and quality of the crop. Proper nitrogen management is essential for growers to optimise their hop yields and ensure the long-term sustainability of their operations.

Nitrogen application methods and timing affect hop yields

Nitrogen application methods and timing have a significant impact on hop yields. Proper nitrogen application and timing are crucial for maximising hop yields. Nitrogen is an essential plant nutrient required for optimum cone production. The nitrogen replacement value, or the amount needed to replace what has been taken up by the plant biomass for fully-grown bines, is approximately 110 lbs/ac/year.

The active growing season's nitrogen uptake can be divided into three phases in hop production. During Phase I, which occurs in early spring, nitrogen uptake is slow and corresponds with slow plant growth. Phase II is marked by rapid nitrogen uptake and pronounced biomass accumulation. Phase III is a period of minimal nitrogen uptake.

Nitrogen fertiliser rates, timing, and application methods depend on various factors such as soil type, climate, plant age, expected yields, and cultivar. For instance, in mature Oregon hop yards, nitrogen application rates based on nitrogen uptake data range from 100 to 150 lbs/acre. In contrast, a common fertility regime in and around Yakima Valley, Washington, involves applying 100 lbs of nitrogen by May, increasing to over 200 lbs through mid-July.

Hop growers are recommended to apply at least 200 lbs of actual nitrogen per acre per year to mature hop plants. Near the end of June, the internode length should measure around 8 inches. If it is less than 8 inches, growers should increase nitrogen levels; if greater than 8 inches, nitrogen levels should be reduced.

Nitrogen use efficiency for hops is around 50%

Nitrogen is an essential plant nutrient for hops, required for optimum cone production. The nitrogen replacement value, or the amount needed to replace what has been taken up by the plant biomass for fully-grown bines, is approximately 110 lbs/ac/year. However, the nitrogen use efficiency (NUE) for hops is only around 50%, meaning that about half of the nitrogen applied is lost to the environment, usually through leaching or volatilisation. This suggests that hop growers should apply double the amount of nitrogen that the plant needs, or 220 lbs of actual N/ac/yr.

The NUE for hops can vary depending on site-specific characteristics such as soil quality and management practices. For example, hops grown on sandy soils with low soil organic matter levels may need higher rates of nitrogen to optimise growth. Similarly, the type of nitrogen applied can affect NUE, with liquid nitrogen fertigation resulting in less loss than a single spring banded application.

To optimise growth, it is recommended that hop growers apply at least 200 lbs of actual N/acre/yr to mature hop plants. Growers can assess whether their plants are receiving enough nitrogen by measuring internode length near the end of June. If the length is less than 8 inches, more nitrogen is required. Signs of nitrogen deficiency include stunting, yellowing leaves, reduced growth, and poor cone development.

Nitrogen is required by hops from the moment they break dormancy, as they use carbohydrate reserves from the previous season until photosynthesis resumes. The total nitrogen applied each season should be around 110 lbs/ac/year, but this can vary depending on the hop variety and soil type. For example, baby hops or first-year plants require less nitrogen, at about 80 lbs N/ac in total.

Nitrogen fertilisation impacts hop aroma compounds

Nitrogen fertilisation is a key factor in hop cultivation, influencing both yield and the chemical composition of the cones. Optimising nitrogen applications and timing is crucial for maximising hop yields, with nitrogen being essential for cone production. The nitrogen replacement value, or the amount needed to replace what has been taken up by the plant, is approximately 110 lbs/ac/year. However, due to factors such as leaching and volatilisation, the nitrogen use efficiency (NUE) for hops is only around 50%. This means that growers should apply twice the replacement value, or 220 lbs of actual N/ac/year, to ensure adequate nitrogen availability for the plants.

The impact of nitrogen fertilisation on hop aroma compounds is an area of active research. A study by Czubacka et al. (2024) investigated the effect of reduced nitrogen fertilisation on the expression of genes involved in the production of bitter acids and xanthohumol, as well as the content of these compounds, in two hop cultivars. The results showed that a 25-30% reduction in the nitrogen dose did not significantly affect the expression of most genes or the content of secondary metabolites. However, the nitrogen dose did influence the activity of specific genes, and differences in gene expression were observed between cultivars and developmental stages.

While the study by Czubacka et al. (2024) did not find a direct link between nitrogen fertilisation and hop aroma compounds, other factors related to nitrogen management may play a role. For example, the timing and method of nitrogen application can affect nitrogen uptake by the plant, with liquid nitrogen fertigated during the vegetative growth period potentially being more effective than a single spring application of banded nitrogen. Additionally, the type of fertiliser used, such as chemical or organic options, may influence the availability and uptake of nitrogen by the hop plants, which could indirectly affect the production of aroma compounds.

In conclusion, while nitrogen fertilisation practices may not have a direct and significant impact on hop aroma compounds, they are crucial for optimising hop yields and cone quality. Growers should aim to balance nitrogen applications to meet the nutritional needs of the plants while also considering the environmental and economic implications of nitrogen use. Further research is needed to fully understand the complex interactions between nitrogen management and the production of hop aroma compounds.

Nitrogen fertilisation affects hop flavour and bitterness

Nitrogen fertilisation has a significant impact on the flavour and bitterness of hops. The level of nitrogen fertilisation can affect the expression of genes involved in the synthesis of bitter acids and prenylflavonoids, which are responsible for the bitter taste of hops.

A study by Czubacka et al. (2024) found that reducing nitrogen fertilisation by 25-30% did not significantly impact the expression of most genes related to the synthesis of bitter acids. However, the activity of genes such as BCAT2, HS1, and PAL was influenced by the amount of nitrogen applied. The study also found that the reduction in nitrogen fertilisation did not result in a decrease in the content of secondary metabolites, including bitter acids and prenylflavonoids.

Another study by Rodolfi et al. (2023) investigated the effect of different organic foliar fertilisation treatments on the hop oil profile and the flavour of derived beers. The study found that nitrogen fertilisation influenced the biosynthesis of terpenes, which are important aromatic compounds in hops. The results showed that the application of nitrogen fertiliser increased the biosynthesis of monoterpenes while decreasing the biosynthesis of sesquiterpenes. The sensory analysis revealed that consumers preferred the beer produced with hops fertilised with Treatment 1, which had higher levels of monoterpenes.

Nitrogen fertilisation can also affect the bitterness of hops through the formation of humulinones. Humulinones are formed by the oxidation of alpha acids in hops and contribute to the bitterness of beer. The solubility of humulinones allows them to be introduced into beer through dry hopping, which can affect the final bitterness levels. The study by Maye, Smith, and Leker (2016) found that dry hopping can either increase or decrease the bitterness of beer, depending on the starting IBU levels.

Overall, nitrogen fertilisation has a significant impact on the flavour and bitterness of hops. The level and type of nitrogen fertilisation can affect the expression of genes related to bitter acid synthesis, the biosynthesis of aromatic compounds, and the formation of compounds that contribute to bitterness.

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