1. Why Does the Same Hop Do Different Jobs Depending on How Long It Is Boiled?
In 2022, a limited beer made with domestic hops was brewed at a Kirin factory. For many regular products, equipment automatically adds hops to the boiling tank. However, for this limited edition, it is reported that people added the hops by hand. [4] The article highlights that human involvement was part of the process.
The timing of adding hops is thought to affect the final beer. In brewing explanations, hops boiled for a long time mainly provide bitterness, while hops boiled for a short time provide flavor and aroma. [1] In general beer making, hops are basically added during the boiling stage. [4]
Why does the same hop change its role based on boiling time? The answer lies in the nature of the aroma source.
2. What Happens to Hop Aroma Compounds Like Linalool When Hops Are Boiled?
Linalool is considered the most important aroma compound in hops. It has a flowery scent and is also found in lily of the valley and lavender. A study by Kyoto University shows that linalool accumulates especially in the cone (the flower-like part) of the hop plant. [3]
These aroma components have a property called volatility, meaning they escape easily into the air. A brewing magazine called BYO explains that volatile oils fly off and are lost relatively quickly from the wort. [2] How much remains depends on the type of hop and the boiling conditions.
Bitterness sources do not become bitter unless they are boiled. The same article states that boiling is necessary to change the bitterness source into its bitter form. [2]
In short, bitterness increases with longer boiling, while aroma flies away with longer boiling. Because their properties are opposite, brewers shift the time of adding hops to separate their roles. Adding hops at the end of the boil is a method used to preserve aroma. [2] So, how do you stop aroma from flying away during boiling?
3. What Does Dry Hopping Do When Hops Are Added After the Wort Has Cooled?
There is a method called dry hopping, where hops are added after the wort has cooled and boiling has stopped. According to BYO, dry hopping does not easily add bitterness because boiling is required to create the bitter form. Instead, the volatile oils are not boiled away, so the aroma can be kept in the final beer as much as possible. [2]
However, it is not always perfect. According to Kirin’s explanation, dry hopping after cooling tends to produce a pine resin-like aroma. [5] This is one manufacturer’s description and may not apply to all cases.
Aroma flies away during boiling, and bitterness is hard to add after cooling. Another method aims for a balance between keeping aroma and limiting bitterness: adding hops during fermentation.
4. Does Adding Hops with Yeast During Fermentation Change More Than Aroma?
Kirin Beer established the "Dip Hop" method in 2011, and it was introduced in a 2021 product presentation. This method involves adding hops together with yeast during beer fermentation. [5] Fermentation here refers to the process where yeast eats sugar to create alcohol.
The explanation states that adding hops at the end of boiling can add bitterness, while adding them after cooling tends to create a pine resin aroma. The Dip Hop method is said to avoid both and produce aroma. [5]
A presentation abstract by a Kirin researcher reports something unexpected. Adding hops during fermentation not only suppresses bitterness and adds a bright aroma, but it also promotes yeast fermentation and reduces unwanted sulfur-like smells. [6] It seems the hop, thought of as an aroma agent, also affects the yeast’s work.
However, this is one manufacturer’s method and research. It is not a comparison of which company’s method is better.
5. Are Some Hop Varieties Better Suited to Bitterness and Others to Aroma?
It is said that some hop varieties are suited for specific roles. There are varieties with high alpha acids (the source of bitterness) for bitterness (bittering), varieties with many aroma oils for aroma (aroma), and intermediate varieties for both (dual purpose). [7] Aroma-oriented varieties are said to often have lower alpha acids.
However, the classification of specific varieties varies between sources. This article does not classify specific variety names.
Adjusting bitterness and aroma depends on both the timing of addition and the type of hop used. A recent presentation abstract notes that demand for beers emphasizing hop aroma has increased due to the craft beer boom. [6] Aroma techniques seem to be becoming more important.
What kind of aroma do hops grown in Japan have, and what challenges do they face?
6. How Does Drying Harvested Hops Affect Their Fresh Aroma?
Harvested hops spoil easily, so they are dried with warm air for storage. However, Kirin explains that during this drying process, the fresh aroma of just-picked hops is lost. [9]
One way to make use of this lost aroma is a beer made with fresh, just-picked domestic hops. In 2004, "Ichiban Shibori Toretate Hop Nama Beer" (First Press Fresh Hop Beer) featuring the name of Tono was released. [9]
Japanese hop varieties also have distinct aromas. "IBUKI" is said to have a refreshing citrus scent like grapefruit, and "MURAKAMI SEVEN" is said to have a Japanese citrus scent like mandarin orange and fig. Kirin uses contract farming for these. [8]
On the other hand, domestic hop production is decreasing due to a shortage of successors and aging farmers. Over the past 10 years, the company’s contract farming area and harvest amount have halved. Efforts to support production areas, such as renovating drying facilities, are progressing. [8]
7. Can You Test How Timing Changes Flavor at Home Using Tea?
Beer is an adult drink, so children should not drink it. Hops are hard to find, so you can try testing how time changes flavor using common tea.
Be careful of burns and always do this with an adult. Prepare two tea bags of the same type. Steep one in a cup of hot water for 30 seconds, and the other for 5 minutes. Compare the smell and taste. Since tea is a different plant than hops, the same change may not happen. However, it is an experience of how the outcome changes with steeping time.
For those who want to learn more, you can read Kyoto University’s announcement about genes that create hop aroma [3] and a Japanese presentation abstract about adding hops during fermentation. [6]