| Jr. Feature |

From Seaweed to Sushi

You do know that the dark stuff wrapped around the sushi rice is seaweed, right? 

The Scoop on Seaweed

You know what the sea is. And you know what a weed is — those pesky plants that grow and grow and overrun any garden you try to maintain unless you remove them consistently. Doesn’t matter if you’re growing cherry tomatoes or roses — weeds will crop up and take your precious plants’ water, space, and nutrients from the soil, unless you get rid of them first. So seaweed must be the pesky plant of the sea, right?


Seaweed is important.

What is seaweed?

Imagine you had a fancy doll — maybe a china doll or an American Girl doll. It has adorable clothing and accessories, beautiful hair and delicate details. You take care of it very carefully. Now imagine someone calls it a regular doll, just like your baby sister’s limp, scruffy rag dolls. They might both be dolls, but you can’t really compare them.

Just like there are different kinds of dolls, seaweeds are one big name for many species. They might all be marine plants (water plants), but there are so many different kinds, and they’re all different from each other. And they grow not just in the sea, but in rivers, lakes, and other bodies of water, too.

Some kinds are tiny, microscopic; others are enormous, growing like huge trees in forests, in the ocean. Most are medium-sized. Seaweed can be red, brown, green, or black. They have different names and different qualities and grow in different kinds of waters and at different depths. And unlike their land-growing namesake, which are considered nuisances, seaweeds are absolutely essential to the health of our oceans. Seaweeds serve as food and as homes for many ocean creatures, and not only that, they benefit people, too. Not just in sushi! Seaweed has been used to heal people for thousands of years; the ancient Romans used seaweed to treat wounds, burns and rashes, and there is evidence that suggests that the ancient Egyptians used them for healing, too. They somehow discovered that many kinds of seaweed contain healing properties such as anti-inflammatory and anti-microbial agents. (Anti-inflammatory means something that can help fix swelling, redness, and pain in the body, and anti-microbial means something that kills harmful things like bacteria and mold so they can’t make you sick.) Seaweed is being researched for powerful cancer-fighting agents; scientists hope that they will be able to harness these powers to eventually help cure sick people. Not only that, but seaweeds are also being used as binding agents, also known as emulsifiers, in products like toothpaste. Seaweed is even being used in specialized, organic skin care products. By now it should be no surprise to you to learn that seaweed is bursting with vitamins, minerals, and fiber. And many of the edible varieties can be tasty, too!

So seaweed, far from being a weed, is a helpful and amazing plant. But how does it get from its ocean home to your table?

How Seaweed Becomes Sushi

No, you don’t just tear some seaweed growing in the ocean and wrap it around your sushi rice.

The kind of seaweed used to make sushi rolls is called “nori.” It’s (obviously) one of the edible types of sushi, and it’s described as having a mildly sweet, salty taste. Growing nori is a process, and then taking the nori and making it into the sheets that will then become your sushi roll takes more work.

Let’s look at some of the steps involved in these processes.

Step One: Seaweed
  1. Cultivation means sprouting baby nori plants. This first step begins on land, when nori seedlings are germinated (sprouted) on special nets called cultivation nets. As the nori seedlings sprout, they attach themselves to the net. The nets are then refrigerated until ocean conditions are ideal for the nori to be installed in the seabed.
  2. Growing is a month-long process. After installation, the nets are not just left for the nori to do its thing. To the contrary, the nets are raised or lowered as needed for the nori to grow optimally; during low tide, the nori seaweed buds must dry above sea level, which means they need to be out of the water. In Japan, where lots of nori is produced, workers on special boats make sure to keep the nets of growing nori at just the right level at all times. Huge fields of floating nori nets stretch as far as the eye can see, bobbing in the sparkling waters.
  3. Harvest means gathering the fully-grown nori. Once it is fully grown and about 20 centimeters long, the nori nets are removed from the ocean by boat and brought to the production plant.
Step Two: Production

The raw seaweed still has to become sheets of nori that can be sent to chefs, restaurants, hotels, and supermarkets all over the world. Here’s how that happens:


When the nori first gets to the production facility, it is cleaned with either fresh water or sea water. Then the nori is filtered so that anything that doesn’t belong in your sushi doesn’t stay around (like dirt, shrimp, and ocean insects).

Mincing and mixing 

Once the nori is clean, machines chop the nori into tiny pieces. Then it’s mixed with fresh water. The mixture is pressed, or poured, into square molds. (This is when the nori actually starts looking like what might eventually end up being a sheet of sushi paper.)


The watery nori mixture needs to dry. Different production plants use different methods of drying, such as fans, pressing, and drying machines — utilizing hot air. The dried squares of nori come off a conveyer belt and are automatically sorted into neat piles of sheets.

Quality Insurance

The sheets are inspected for quality and consistency. Companies make sure that the nori sheets have the same moisture content and same thickness. They also ensure that the filtering was successful, and that no foreign objects were left behind. To do this, the sheets are scanned by lasers that pick up anything that does not conform to the texture and color of the nori (more on that soon).

Toasting or roasting  

The approved sheets are loaded into special machines that roast or toast them. Here, too, different companies use different methods, some toasting for longer than others, and at different temperatures. That’s one of the reasons why different brands of sushi nori taste different.

Additional processing 

Some nori sheets are not going to be used to make sushi. There are different products made with seaweed, like seaweed snacks or garnish. Some of the sheets are ground into powder to be used as flavoring. Other sheets are left large for preparing sushi. Sometimes the sheets are flavored with various flavorings.


Once the product is finally complete, it’s ready to be packaged. Nori products are sealed in special packaging to preserve them and keep out moisture (which could cause the sheets to spoil).

Shipping and selling   

The sheets of nori are on their way to your local sushi bar or grocery store!

Kosher Consumer

Seaweed – seems like it’s as kosher as it can get, right? I mean, it’s an ocean vegetable. Aren’t all vegetables kosher?

Not so fast.

There are potential issues in seaweed, so next time you want to make sushi or sushi salad, it’s very important to purchase nori with a reliable hechsher. And if you’re talking about buying the actual product – sushi – a reliable hashgachah is even more crucial. Here, several kashrus agencies share common pitfalls.

Plain Nori Sheets

Yes, veggies are kosher. But you know that many vegetables need to be checked – your mother wouldn’t dream of using unchecked lettuce. Even if your family buys the prewashed and checked kind, someone had to make sure there were no forbidden creepy-crawlies in there. Same goes for seaweed, a plant which grew in the ocean wild, and could potentially harbor infestation. A common culprit is baby seahorses (yuck). Sometimes these tiny baby seahorses, or baby shrimp, manage to sneak past the companies’ quality control checks and those laser beams, which is why it is so important that your nori sheets have a reliable hechsher to assure you that no, there are no baby seahorses in your sushi!

In addition, some companies use flavorings, sugar, or colorings to enhance their nori sheets. Of course, all of these can cause potential kashrus issues, too.

Ready-Made Sushi

Once the nori is part of an actual piece of sushi, the issues grow exponentially. Kashrus companies are quick to point out a myriad of potential problems. Here are just some of them:

The Fish: Lots of people like their sushi with raw fish (not my thing, but okay). They might think that seeing as it’s fish, and it’s raw, there are no issues with it. Wrong! We all know that to be kosher, fish needs to have fins and scales. Tuna sure fits the bill, so if it’s a tuna sushi roll then it must be fine, right? Wrong again! There have actually been recorded cases of other fish being substituted and sold as tuna. To make matters worse, some sneaky people figured out a way to get around the requirement of pas kaskeses. That means that although a small patch of skin with visible scales is left on the fish, which is a proof of its kashrus, cheaters cheat. They take any old scaled skin patch and paste it onto the unkosher fish! Because of the enzymes in the fish and the skin, and because the fish is subsequently frozen, it looks like the scales are completely natural when really, they’re completely not. A reliable kashrus agency knows to be on the lookout for this issue, to make sure that the tuna sushi being served at the kiddush is completely kosher. And not only that, but the raw fish is often soaked in various solutions before use, which may contain unkosher ingredients – which are then absorbed by the fish. Here, too, a reliable kashrus certification will ensure this mixture is fine for the kosher consumer. They will also make sure that there is no cross contamination with treif fish or treif food colorings. And if the fish happens to be cooked, the kashrus agency will take care that it was not cooked on Shabbos and that it was not cooked by a non-Jew, which would render it bishul akum.

The Wasabi: This strong condiment that many people enjoy with their sushi isn’t just a grated vegetable. Because real wasabi is rare and expensive, most commercial wasabi is really just horseradish, mustard, and green food coloring. Which, of course, needs kashrus certification.

Dippings: Soy sauce, teriyaki sauce, sweet chili sauce, and spicy mayo are all popular dipping sauces for sushi. Most brands contain lots of ingredients and all of them must be certified kosher!

The Ginger: Pickled ginger, another favorite sushi accompaniment, is often prepared in vinegar, which always requires a hechsher. And even if it was pickled in plain salt water, it’s considered a davar charif – a sharp food – which requires more caution in terms of contact with unkosher utensils. Because sugar and colorings are also added to the ginger, it’s crucial that your ginger be properly kosher-certified.

The Rice: While plain, raw rice is kosher, many companies use instant rice or parboiled rice, which means it was partially or completely cooked before packaging. Thus, it too requires a good hechsher.

From the salty ocean water to busy production plants and careful mashgichim, who ever knew there was so much going on behind the scenes with sushi in general, and kosher sushi especially? So whether you like sushi or think it’s awful, next time you see a roll, think of everything that went into preparing it!

Many thanks to the Vaad Hakashrus (Five Towns Far Rockaway), CRC (Chicago Rabbinical Council), COR (Kashruth Council of Canada), and Star-K for information on the potential hazards of sushi and nori.


(Originally featured in Mishpacha Jr., Issue 927)

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