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For me, the best thing about sushi is the wasabi—that sinus-clearing green paste that adds just the right amount of heat to the fish and rice. Unfortunately, it’s not actually wasabi. It’s usually a mixture of horseradish, mustard, soy sauce and green food coloring that is supposed to mimic both the taste and the color of freshly grated wasabi.
The wasabi plant (Eutrema japonicum) is a brassica, related to cabbage, broccoli, mustard and horseradish. It is native to Japan where it grows along the shady banks of cold mountain streams. It is extremely difficult to grow outside of its native habitat, creating a scarcity that has resulted in high prices. Adding to the price is the fact that after it is grated, the flavor only lasts for 15 minutes. It cannot be preserved like horseradish. Also, unlike horseradish, the “root” of the wasabi plant that is used is actually the stem.
It is nearly impossible for a home gardener to grow wasabi because it has very particular needs. The most important is cold, flowing water. It does not grow in standing water like water lilies. Remember, in its native environment, it grows along mountain streams which frequently overflow their banks, creating the flow of cold water that the plants need. Its other requirement is shade, not found in most vegetable gardens.
Attempts have been made to grow wasabi in greenhouses and hydroponically. Both have their issues, the most pressing is trying to grow the plants in standing water.
The Japanese are able to farm wasabi. The farms are located in the mountains, usually along streams. This is important because the plants need both the cooler air temperature and cooler water temperature of higher elevations. Warmer air results in damage to the plants and increases their risk of succumbing to fungal disease. The garden plots are on terraced land so that water can flow over the plants without immersing them, mimicking their natural habitat of stream banks. Shade is provided naturally by surrounding trees or by elaborate structures supporting shade cloth.
Wasabi is easy to propagate because of the way the plants grow. Small plantlets develop around the crown of the plants. These plantlets are broken off at the time of harvest and replanted. This can be done for only a few years due to disease. The wet environment that the plants grow in encourages disease. Because the plants require such a specialized environment to grow in, it is not possible to use crop rotation to prevent disease from infecting both the mother plants and the plantlets. After a few years, fresh plants that are not infected with disease must be grown from seed.
The seed requires cold stratification to germinate, approximately two months at 40⁰F so the seeds are usually planted in February and March. Germination takes two months. The plant will be mature enough to flower the following year. Flowering begins in January and ends in May. Seedpods are ready for harvest 50 to 60 days after the plants have finished blooming.
Wasabi is harvested in its second year of growth. Ideally, the stems should be six inches long and two inches in diameter. Harvest is done by hand. Each plant is carefully pulled from the soil and washed. Roots that are adhering to the stem as well as dead leaves are removed. At the same time that the plants are harvested, the small plantlets that surround the crown are broken off and replanted for harvest the following year.
Harvested stems must be stored in a cold, humid environment. When displayed in a store, misting is a must. The stems need humidity to prevent them from drying out and becoming useless.
The most traditional way to serve wasabi is to grate it just before serving. In high end restaurants, the stems are grated tableside so that customers know that they are getting peak flavor. Any kind of grater can be used. The preferred grater is made of wood with a piece of shark skin attached to it. The rough shark skin produces finer shreds than manmade metal graters.
The characteristic green color comes from the color of the stem. The stems are graded according to their shade of green. A medium green is the most desirable and has the highest price. Dark green or light green stems are less desirable or even considered unsuitable for eating and have much lower prices.
Wasabi can also be dried and ground into a powder that can be used to flavor food or combined with other ingredients to make a paste.
So the next time you are dining in a Japanese restaurant, inquire if they have fresh wasabi and try some with your dinner. Be warned though, once you’ve tried the real thing, that green paste that comes with your sushi will never be quite the same.
© 2018 Caren White
Caren White (author) on January 05, 2018:
Natalie, the plant is adapted to a specialized environment requiring flowing water. A lot of different methods for growing it have been tried. Most have failed. Fresh wasabi is not as harshly hot as the fake stuff we are used to. The flavor is hot but more mellow.
Caren White (author) on January 05, 2018:
Mary, I was also surprised by it. Thank you for your compliments. Glad you enjoyed the read.
Natalie Frank from Chicago, IL on January 05, 2018:
I never thought about the wasabi that comes with sushi other than to make sure I haven't put too much on a single bite lest I end up dancing around sniffing and saying, "Oh my G-d, it's hot!" over and over. I didn't realize it was an actual plant like horseradish. That's so interesting the way it is grown. What is it about the flowing water that makes such a difference? Would it be possible to grow it in some sort of fountain like mechanism which can be filled and drained and made to circulate even if it didn't flow past the plants? Or is there something that would lead to disease if the water doesn't flow past the plants? Is it much hotter than the green wasabi paste? Sorry for all the questions - your article made me inquisitive. Thanks for the info!
Mary Wickison from Brazil on January 05, 2018:
I am surprised by this, as I assumed it grew like a radish.
How fascinating to know about the wasabi. You're right, it does clear out the sinuses when eaten.
Interesting topic and excellent images.