Series: The Search for New Seeds of Shikohin Ideas

According to the 7th Edition Kojien (Japanese dictionary), shikohin is defined as “Food or beverages that are consumed for flavor, fragrance and stimulation over nutritional value. Examples include alcohol, tea and coffee.” Nonetheless, many people would also describe shikohin products as a necessity in their day to day lives. If shikohin products do not provide us with any nutritional value, are they really a necessity?

Rei Horie, founder of craft gin maker HOLON, believes otherwise. She says, “Shikohin provides nourishment to our souls that gives us the energy to carry on in our daily lives.” 

So what role will shikohin play in our ever changing world and unforeseen future?

In this series, “The Search for New Seeds of Shikohin Ideas” Rei Horie will meet with experts from various fields to identify and record new seeds of possibility in the world of shikohin. 

These records will assist in the sprouting of such seeds in the near future. 

For this article,we visited the Forestry and Forest Products Research Institute in Tsukuba City, Ibaraki Prefecture.  

We had heard that the institute (hereafter referred to as the Forestry Research Institute) had successfully developed a groundbreaking technology to produce alcohol from wood.  Sensing the potential for a new shikohin product, Horie and the Dig The Tea team set out to meet Yuichiro Otsuka, the creator of this innovative “wood sake” .

During our visit, we sampled various tree-derived alcohols, including those made from Japanese cedar, wild cherry, mizunara oak (Quercus crispula), and white birch. We also explored the future possibilities of this emerging shikohin experience.

The new technology behind fermenting wood into alcohol

Horie: A growing number of liquors are emerging in the market that highlight the fragrances of wood, such as the craft gins Kanamori, KODACHI, and Forest Gin. However, I’ve heard that the technology developed at the Forestry Research Institute has created a “wood sake” using a completely different method from conventional techniques.

Otsuka: Typically, when making liqueurs with woody aromas, the common approach is to use a base liquor—such as a distilled spirit—and either infuse it with wood or age it in wooden barrels, as is done with whiskey. We have developed a method that ferments the wood itself to make alcohol. 

Horie: So your method involves fermenting and distilling the wood itself, rather than simply transferring its aroma into a liquor or distilled product! That’s a completely new approach—I’ve never heard of anything like it before. Why has it been so difficult to turn wood into alcohol in the past?

Otsuka: Wood takes a long time to break down naturally. If a tree falls in the forest, it can take decades to fully decompose. This durability is why wood is such an excellent building material—but it also means that fermenting it is extremely challenging. Our new technology allows us to overcome this hurdle.

Let me walk you through the actual process of turning wood into alcohol. First, we use a wood chipper to break the wood down into sawdust. Then, we put the sawdust into a machine called a pin mill—commonly used in food processing to make soybean flour and other fine powders—to grind it even further into a fine, flour-like consistency.

Horie: What do you do with the tree bark?
Otsuka: The bark can be covered in moss or mold, which makes it unhygienic, so we remove it before processing.

Otsuka: The next step is a very important one in the process of turning wood into alcohol. The finely ground wood is processed in a machine called a beads mill. This machine contains small beads that collide with each other at high speeds, further refining the wood flour into an ultra-fine cream-like paste.

Interestingly, the bead mill was originally developed for ink manufacturing. In fact, the ink used in the popular “Jetstream” ballpoint pen is refined to the nano level using this very technology, which gives the pen its famously smooth writing experience.

Horie: So this process reduces the wood to particles just one micrometer in size! Why is that so important for making alcohol?

Otsuka: Take sake-making, for example. In sake production, enzymes from koji mold break down rice starch into glucose, which then feeds the yeast needed for fermentation. In the case of wood, cellulose plays the same role as rice starch—but it’s protected by a tough cell wall. Even if we add enzymes, they can’t penetrate the cell walls to start the saccharification process.

To overcome this, we need to grind the wood into particles finer than the cell walls, which are about 2–4 micrometers thick. Only then can the enzymes break down the cellulose into fermentable sugars.

Horie: So once saccharification occurs, yeast can be added to start fermentation and produce alcohol?

Otsuka: Exactly. By turning wood into a cream-like paste, we make it accessible to microorganisms, allowing fermentation to take place. However, even after fermentation, the alcohol content is only around 1–3%, which is much lower than typical alcoholic beverages.

This is due to the properties of cellulose—it absorbs water and expands. During the beads milling process, if there isn’t enough water, the mixture becomes too thick and clogs the machine. To prevent this, a large amount of water must be added, which dilutes the alcohol content.

To concentrate the alcohol, we then use a vacuum distillation process to produce a higher-purity distilled spirit.

Tasting the Wood Alcohol

Horie: Since the alcohol content is relatively low, do you see potential for creating non-alcoholic products with this process?

Otsuka: Perhaps that is possible, but the fermented state has a strong bitterness, making it difficult to drink as is—it’s like chewing on raw wood. Once distilled, the aroma and alcohol are concentrated, making it much smoother and more enjoyable.

That said, distillation can sometimes refine the liquid too much. We’ve experimented with blending the unrefined alcohol back in, which results in a richer, heavier sweetness drawn from the wood itself. To get a better sense of the flavors, please try these four distilled spirits.

Horie:The white birch has such a crisp, clean taste, with a fruitiness reminiscent of pear or green apple—it’s delicious! The mizunara oak (Quercus crispula), which is often used for whiskey barrels, really captures the essence of the wood itself. It has a creamier, more rounded flavor compared to the white birch. The Japanese cedar has a deep, forest-like character, but I also detect a hint of cocoa.

Otsuka: The Japanese cedar tends to leave the most varied impressions. This particular cedar came from Tokigawa in Saitama Prefecture. We counted 44 rings, meaning the tree was 44 years old. In some areas, there are trees that are over 200 years old, so this was a relatively young tree. 

Horie:  It’s almost like drinking the history of the tree itself.

Otsuka: Kuromoji is well known for being used in high-end toothpicks. It’s an incredibly fragrant tree with a refreshing, vibrant aroma. Most of its fragrance comes from the inner bark, but the thicker the trunk, the weaker the scent. On the other hand, thinner trees are highly aromatic but contain less cellulose, which is necessary for alcohol production. We are currently experimenting with different trunk thicknesses to determine the ideal stage for processing.

Horie: Compared to fresh kuromoji branches, the distilled alcohol has a cooler, more refined herbal scent—it goes straight through the nose.

Otsuka: Next up is our spirits. Actually, the wild cherry trees resulted in a very green, grassy aroma when distilled. The volatile aroma alone wasn’t very pleasant, but the moromi (fermented mash) had a very rich fragrance that we wanted to make use of. We created a spirit that blended the distilled liquor with the moromi. 

Horie: It has a sweet fragrance similar to sakura rice cakes. It also smells a lot like the fallen leaves of cherry trees. I also taste a hint of a rich sweet and sour flavor similar to plums.

Otsuka: Now, please try the spirits we made using the distilled spirits you tasted earlier. 

Horie:  The white birch has an intriguing, almost salty note. The Japanese cedar and kuromoji have an even more intense wood aroma compared to their distilled spirit counterparts.

Otsuka: We’re not entirely sure where that salty note comes from. It’s a unique characteristic—some people love it, while others find it unexpected.

Horie: The mizunara has an entirely different impression from its distilled version. It has a deeper vanilla-like sweetness and a mellow richness, almost like a beautifully aged whiskey. This is incredible!

Otsuka: If you enjoyed the mizunara, you should try the konara (Quercus serrata). It’s closely related to American white oak, commonly used in bourbon barrels, so it carries a similar bourbon-like aroma.

Horie: The konara has a slightly rougher finish compared to mizunara, but it also has a distinct sweetness, almost reminiscent of tonka beans—the fragrant seeds of the cumaru tree from South America.

Otsuka: As a producer, I find it fascinating that even trees within the same oak family can have such different characteristics. According to one study, Japan is home to approximately 1,200 different tree species. That means there are potentially 1,200 unique flavors to explore.

Horie: What kind of safety tests have you implemented in the process of making beverages from trees?

Otsuka: Currently, there are no established safety testing standards for this in Japan. However, as a manufacturer, we bear full responsibility for ensuring the safety of our products, and we would immediately halt production if any concerns arose. That’s why we conduct our safety tests in accordance with EU safety standards.

Specifically, we perform component analysis to check for harmful substances and conduct tests on rats. One of our biggest concerns was the potential presence of methanol, but to our surprise, the analysis detected almost none, and we successfully passed safety evaluations.

Wood has also been used in food-related industries before. For instance, disposable chopsticks are made from Japanese cedar, kuromoji is traditionally used for toothpicks, and mizunara oak is commonly used in whiskey barrel production. Because of this, we initially focused on trees that already have some history of being verified for safety in the past. 

The potential of tree alcohol in the future

Horie: If wood can be fermented, it seems like it could also be used to create other food products, such as vinegar.

Otsuka: In theory, yes—if we can make it taste good. However, the process of breaking wood down into a paste is very costly, so production expenses are inevitably high. That’s why alcoholic beverages are more viable than non-alcoholic products.

Additionally, making vinegar presents a unique challenge. The fermentation process would have to take place in a completely separate facility from alcohol production. If acetic acid bacteria were to accidentally contaminate the alcohol production area, everything would turn sour.

Horie: One advantage of alcoholic products is that it can be sold at higher prices. 

Otsuka: Exactly. There are cases where overgrown cedar trees become too large to process at lumber mills, making them unsuitable for construction materials and lowering their market value. Even if they do make it to market, they might sell for just a few thousand yen per tree. However, if we turn that same wood into alcohol, it can yield products worth several tens of thousands of yen.

Another advantage is that because we grind the wood into powder, we can utilize trees that wouldn’t typically be suitable for lumber.

At the Forestry Research Institute, our mission is to increase the demand for domestic timber and strengthen the forestry industry. At the same time, we aim to establish sustainable forestry cycles. Adding value to wood-based alcohol is an ongoing challenge, but perhaps one idea would be to create local brands that highlight both the wood and the natural spring water from each region.

Since we are a research institute, we do not manufacture or sell products ourselves. For wood alcohol products to reach the market, private breweries must take on the production and sales. Currently, two Japanese distilling ventures, The Ethical Spirits&Co. and Murakami Lumber Co,  are working to establish wood alcohol as a viable business. The Forestry Research Institute is still seeking brewers who are willing to take on the challenge of producing wood alcohol using our technology.

Horie: Tasting wood alcohol made me reflect on the time and places these trees have experienced throughout their lifetimes. There’s something romantic about a flavor that transcends time and space. I look forward to seeing wood alcohol become more widely appreciated in the future.

Seeds for Shikohin 01

Each tree carries a unique fragrance, offering a vast range of aromatic possibilities. By combining fermentation and aging techniques, we have the potential to create tens of thousands of distinct fragrances. We aim to further explore how different tree varieties can be transformed through these processes.

Seeds for Shikohin 02

People are drawn to flavors that are cultivated over time and the stories behind them. This enhances appreciation for the product and the shikohin experience. The very essence of wood alcohol, which is the trees themselves, embodies time and history, just as their growth rings tell a story of time. How these stories will be told and how people will find shikohin experiences through them would be interesting to see.  

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Translation: Sophia Swanson