Traditional Soy Sauce Brewing | A Portrait in the Netherlands

You don't need to travel to Japan to see how soy sauce is made. In Rotterdam, Thomas Uljee and his three colleagues brew the only traditional soy sauce in Europe. We went to have a look at the brewing barrels.

Thomas Uljee’s soy sauce is called Tomasu, which is Google-Translate-Japanese for ‘Thomas’. “Not out of vanity,” Thomas says. “It just sounded really good.” Thomas is full of energy, sharing one story after another. Starting the soy brewery - or ‘soy house’, which is Thomas’ preferred term, as it resembles French wine houses - was not the easiest feat. As a baker’s son, Thomas had struggled with a big frustration a few years back: time.

“Baking is a beautiful occupation. You work with natural basic ingredients and turn them into something incredibly delicious. But it’s also a huge race against the clock. Time controls the entire production process. From the field, where the farmer needs to produce as much grain as possible per square meter, to the shop, because bread needs to be sold within the day. Time has become such a determining factor that efficiency is valued more than flavour. This really annoyed me. I wanted to do something where time wasn’t an enemy, but a friend. Right at that moment, I saw a documentary on television about Matt Jamie, an American who brews soy sauce in bourbon barrels. I immediately knew: I want to do that too!”

That same day, Thomas booked a flight to Kentucky and knocked on Matt Jamie’s door.

Thomas has another secret card: he chooses to use old Scottish whisky barrels - this is not customary in Japan. “I got the idea from the micro-brewer Matt Jamie in Kentucky; he brews his soy sauce in bourbon barrels. The remaining whisky in the barrels adds an extra flavour.”

Thomas beams when he talks about his wooden barrels. “I think they’re so cool. They’re made of wood, a natural material, and they’re incredibly sturdy. It’s as if the barrels are saying: You just do your thing, and I’ll still be here in fifteen years.” But the barrels aren’t actually kept in the brewery for that long. After 30 months - when the moromi is completely fermented - the soy sauce is squeezed out, filtered and immediately bottled.

Non-pasteurised soy sauce

Photo Credit: Kim Verhaeghe

“Almost all soy sauces in the world are pasteurised. We consciously choose not to do that because it gives better flavour. The sauce is like fine wine, it will continue to evolve - it actually has an unlimited shelf life. By not pasteurising and not using standard soybeans and wheat, we hope to be able to present a new flavour variety every year.”

Chemicals in modern-day soy sauce?
Traditional soy sauce ferments for about two years before it’s ready. In Tomasu’s case, it’s three years. During the traditional fermentation process, the proteins in the soybeans and the wheat are slowly dissolved by the enzymes. But today, bigger soy sauce producers often speed up the process with some chemistry - using hydrochloric acid to make soy sauce in only a few days.

The ‘speedy’ soy sauce is created by mixing soy concentrate, which contains a lot of protein, and hydrochloric acid. The hydrochloric acid dissolves the proteins in the soy concentrate in roughly 20 hours. (In the traditional process, the yeast takes a few years to create the same effect.) After 20 hours, the mixture is neutralised with sodium hydroxide, which creates something that resembles soy sauce. This substance can be seasoned with flavour enhancers like corn syrup, caramel or salt.

This shortcut is fast and cheap, but it has a big disadvantage: 3-MCPD can be a by-product. This is a carcinogenic substance. The substance isn’t found in natural ferments. In 2018, a Dutch television programme showed that almost half of (mostly Chinese and Thai) soy sauces sold in the Netherlands contained 3-MCPD. In most cases, the concentration was below the legally allowed amount. However, one soy sauce contained double the permitted limit.

The author originally wrote this piece for the Belgian outlet Eos Tracé. Read the piece in Dutch here.

What does this soy sauce brewery look like?

Photo Credit: Kim Verhaeghe

Now, four years later, Thomas owns his own traditional soy sauce brewery. The brewery itself is both atmospheric and impressive. Outside, you’re still in the busy industrial area where trucks drive back and forth, but inside the brewery, the sight of numerous wooden barrels seems to make time stand still. It evokes an illusion that Thomas himself imagines: an old wine house, far away from hectic life. The soybeans and wheat bring an intoxicating but pleasant scent to the air. Test bottles, spice jars and books are charmingly scattered around, and the walls are decorated with newspaper clippings and photos. “Our man cave”, Thomas laughs.

Trying different soybeans

Photo Credit: Kim Verhaeghe

When Thomas first had the idea to brew soy sauce, he immediately wanted to do the entire production process himself - and that starts from the ground, literally.

“Soy sauce has four basic ingredients: soybeans, grains, water and salt. Our sea salt is sourced from the French Guérande, and the water is filtered tap water from Rotterdam. For the soybeans and wheat, I looked for a farmer willing to grow wheat with me in an unconventional way. I wanted to experiment with unknown wheat types and give them the time to mature - without using any methods to force them to grow. I wanted to make a choice based on flavour, not efficiency.”

The first farmers Thomas spoke with called him crazy. “They didn’t believe my approach was viable, so they dropped out. In the end, I met Jeroen Klompe, a regenerative farmer from the Hoeksche Waard who had been searching for the same thing for a while.” After Thomas and Jeroen found each other, they teamed up with Wageningen University to start testing different soybeans, as well as so-called ‘forgotten’ wheat varieties. After the soybeans were ripened and dried, they were transported to the brewery in Rotterdam.

The soy sauce brewing process

Photo Credit: Kim Verhaeghe

“We cook the dried soybeans in a large bin. The beans are sieved from the water and mixed with the wheat. Then, we add our fungus, the Aspergillus Oryzae Tomasu. We spread that mixture on large tables in a dedicated room. That mixture is called koji. The fungus then gets to work and activates important enzymes needed in the brewing process.” The room where koji is spread out is warm and damp. “That has to do with the fermentation. We rake the koji every day to keep a constant temperature.”

Koji looks like beans with a layer of whirled-down sand. Thomas taps the beans, and a dust cloud rises. “A sign that they’re ready for the next phase.”In the next phase, the koji and the cooking liquid are poured into a wooden barrel with sea salt to continue fermenting. The reddish-brown slurry in the barrel is called moromi and needs to ferment for around 30 months, because “long fermentation creates a range of aromas and flavours.”

Read Soy Sauce | How It’s Made.