From BLAND to BOLD
THE MAGAZINE DEVOTED TO NICKEL AND ITS APPLICATIONS
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DELICIOUS AND HEALTHY baked tofu: Mix minced garlic, ginger, tamari (soy sauce) and a few drops of sesame
oil. Spread on sliced firm tofu and bake for 20 minutes at 350°F.
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CONSUMPTION OF SOY SAUCE in countries outside of Japan is increasing, most notably in the United States.
To meet that increase in demand, manufacturers need to build new capacity in the next few years.
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WOODEN TANKS have been used in Japan’s soy sauce industry for centuries.
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ONE SOLUTION to the age-old problem of the corrosion of soy fermentation vessels is to make new plants
out of super austenitic stainless steel.
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Adventurous cooks in North America are discovering soy sauce. By Virginia Heffernan
Nickel Magazine, March 2005 -- Connoisseurs of soy sauce are as passionate as beer lovers when
it comes to the colour and flavour of their favourite brew. Indeed, the Japanese take their soy sauce so
seriously that newlyweds have been known to fight over whose brand will dominate in the matrimonial home.
But the same qualities that lend soy sauce its cachet create such severe conditions during fermentation that the stainless steel tanks common to other food-processing industries are not up to the job of brewing the popular sauce. Instead, Japan has tended to use fibreglass and resin-lined steel, both of which resist corrosion.
Problem is, the mix of organic acids and sodium chloride in the sauce is so corrosive and the fermentation process so long (about six months) that the cost of maintaining the tanks can be prohibitively expensive.
The solution to this age-old problem may be at hand. A recent study shows that molybdenum-bearing super austenitic stainless steel S32053 resists the corrosion that affects other stainless steels immersed in conventional brewing tanks.
"The super austenitic stainless steel is less susceptible to corrosion, whereas S31603 suffers crevice corrosion and stress corrosion cracking, and duplex stainless steel S32506 is susceptible to crevice corrosion," writes Yutaka Kobayashi of Nippon Yakin Kogyo, one of the largest stainless steel producers in Japan, in a paper published in Stainless Steel World.
Based on the experimental results, Yamasa Corporation, which has been making soy sauce since 1645, built 100 fermentation tanks in S32053 with capacities of up to 390,000 litres for its Japanese operations. The tanks have been in commercial use since October 2002 without any corrosion.
The brewing process is based on techniques handed down through generations. First, steamed soybeans and roasted wheat are mixed with a proprietary mold to induce fermentation. This mash, called koji, is then mixed with salt and water. During the 6-month fermentation process the ingredients gradually decompose into organic acids, amino acids and alcohols, the combination of which gives the sauce its distinct character.
But these acids also lower the pH to about 4.7 in an already corrosive stew containing about 17% sodium chloride. The fermentation tanks must be able to withstand severe conditions.
If the S32053 tanks withstand the test of time in Yamasa’s plant, their marketability will be significant.
Every year, about 8 billion litres of soy sauce are consumed throughout the world, according to industry
groups. Per-capita consumption in Japan is about nine litres a year, while the corresponding U.S. figure is
just under one litre, and growing.
About 1 billion litres of soy sauce are produced in Japan per year, though this figure has been decreasing
slightly, year by year, because of diversification in Japanese eating habits. Roughly, 1,600 companies
produce soy sauce, the largest of which are Kikkoman, Yamasa and Higeta.
On the other hand, demand outside of Japan, especially in North America, has been increasing rapidly. According to the Soysauce Information Center, 200 million litres of soy sauce were produced outside of Japan in 2002 (25 times the 8 million litres that were produced in 1975), and 10 million litres were exported from Japan that same year.
The opportunities to use super austenitic stainless steel for new fermentation tanks seems great.
Virginia Heffernan is a Toronto-based science writer.
PHOTOS: Tom Skudra for Nickel Institute / Nippon Yakin Kogyo Co. Ltd.
Yutaka Kobayashi For more information on the use of nickel-containing materials in the food process industry see our food and beverage web portal. |
