Understanding Key Hop Compounds: Why Their Differences Matter

As we know, hops contribute not only to the aroma and flavor of beer but also to its bitterness and overall complexity. In this article, we’ll focus on some of their essential oils and compounds, particularly terpenes, thiols, and sulfur-containing compounds.

Let’s start with the basics: what are terpenes?

Terpenes are aromatic compounds found in the resinous glands of hop flowers. Their composition can vary depending on the hop variety, growing conditions, and terroir, resulting in a diverse range of flavors and aromas.

Hop oils are generally divided into three main categories: hydrocarbons, oxygenated compounds, and sulfur-containing compounds.

• Hydrocarbons make up 40-80% of the total oil content and include terpenes like myrcene, humulene, and β-caryophyllene. These compounds are highly volatile and contribute woody, spicy, and resinous flavors to beer.
• Oxygenated compounds, including linalool, geraniol, and citronellol, account for around 30% of hop oils. These compounds are crucial for fruity and floral aromas and play a major role in creating the vibrant, aromatic profiles found in IPAs and other hop-forward beers. Since they are less volatile than hydrocarbons, oxygenated compounds are more likely to remain in the beer after brewing.
• Sulfur-containing compounds, though comprising less than 1% of total hop oils, can have a profound impact due to their low sensory threshold. Thiols, in particular, are essential in modern fruity beer styles like Hazy IPAs, contributing tropical and fruit-forward notes that enhance the beer’s overall aroma and flavor complexity.

What Are These Compounds?

• Myrcene: One of the most abundant terpenes in hops, contributing earthy, spicy, and sometimes herbal notes. It is found in the hydrocarbon fraction of hop oils, which makes up about 40-80% of the total oil content. Myrcene is highly volatile, meaning much of it can be lost during the brewing process, especially if hops are added early in the boil. However, it provides a resinous character that enhances bitterness and depth in hoppy beer styles.

• Linalool: A terpene alcohol in the oxygenated compound group, known for its sweet, floral, and sometimes citrusy aroma. Although it only comprises about 0.5-0.8% of total hop oils in most hop varieties, linalool is still a highly impactful compound in beer. It is less volatile than myrcene, making it more likely to remain in the beer after brewing. Linalool plays a crucial role in dry hopping techniques, contributing bright, refreshing aromas to IPAs and other aromatic beer styles.

• Geraniol: A terpene alcohol in the oxygenated fraction of hop oils, recognized for its strong floral and citrusy scent, often described as similar to rose or geranium. While its direct contribution to beer aromas is valued for its fresh, bright notes, geraniol is particularly significant due to its role in biotransformation. During fermentation, yeast can convert geraniol into beta-citronellol when interacting with certain yeast strains that exhibit β-glucosidase and β-lyase activity. This is why adding hops rich in geraniol during late hopping is important—it helps preserve the compound so there’s enough available for fermentation. Selecting hops high in geraniol, combined with specific yeast strains, can amplify these transformations, creating layers of nuanced aromas in the final beer.

• Citronellol: Known for its woody, fresh, and slightly citrusy aroma, citronellol adds a clean, crisp finish to beers. Like geraniol, it is part of the oxygenated fraction, offering a subtle yet impactful layer to the sensory profile of beers.

Why Is It Important to Know Their Differences?

Understanding the balance between these compounds is crucial. Whether you’re chasing the tropical, fruity notes from thiols or the resinous bitterness from hydrocarbons, knowing how to read lab data and how these compounds interact can help you design a beer that’s perfectly tailored to your vision.