Nigari is the mineral-rich liquid left over after salt is crystallized from seawater. It’s primarily a mix of magnesium chloride and magnesium sulfate (Epsom salts), and it has been used for centuries in Japan as the traditional coagulant for making tofu. You can find it sold as a concentrated liquid or dried into flakes, typically in Asian grocery stores or online.
How Nigari Is Made
The production process is straightforward. Seawater is evaporated until sodium chloride (table salt) crystallizes out. The concentrated liquid that remains after the salt is removed is called “bittern,” and this bittern is nigari. It contains the minerals that were dissolved in seawater but didn’t crystallize along with the salt, primarily magnesium chloride and roughly 4% magnesium sulfate, along with smaller amounts of potassium chloride, calcium chloride, and various trace minerals.
The word “nigari” comes from the Japanese word “nigai,” meaning bitter, which describes its sharp, slightly bitter taste. That bitterness is characteristic of concentrated magnesium salts.
Why It’s Used to Make Tofu
Nigari’s main job in the kitchen is turning hot soy milk into tofu. When you add nigari to soy milk, the magnesium ions interact with soy proteins and cause them to clump together into curds, much like rennet curdles milk into cheese. The curds are then pressed into blocks of varying firmness depending on how much liquid is removed.
Recent research has refined our understanding of how this actually works at a molecular level. Scientists long believed that magnesium ions formed direct bridges between protein molecules, linking them together like rungs on a ladder. But newer findings from 2024 suggest something different: rather than physically bridging proteins, the magnesium ions neutralize the negative electrical charges on protein particles. Soy proteins naturally repel each other because they carry the same charge. Once magnesium strips away that charge, the proteins stop repelling and begin to clump, forming the gel network that becomes tofu.
Tofu made with nigari tends to have a slightly sweet, delicate flavor and a softer, more tender texture compared to tofu made with calcium sulfate (gypsum), which is the other common coagulant. This is why nigari tofu is prized in Japanese cuisine, particularly for silken tofu varieties.
Nutritional Value and Magnesium Content
Because nigari is concentrated seawater minerals, it’s a natural source of magnesium, a mineral that many people don’t get enough of through diet alone. Magnesium plays a role in hundreds of processes in the body, from muscle and nerve function to blood sugar regulation and bone health.
Magnesium chloride, the primary compound in nigari, is a soluble inorganic salt. That solubility matters for absorption. Research on magnesium supplements has consistently shown that how well your body absorbs magnesium depends more on the solubility of the form you take than on how much elemental magnesium it contains. In one study, a more soluble magnesium supplement raised blood magnesium levels by 6.2% after a single dose, while a less soluble form containing more than twice as much raw magnesium only raised levels by 4.6%. Magnesium chloride dissolves readily in water, which puts it in a favorable position for absorption compared to poorly soluble forms like magnesium oxide.
That said, the amount of magnesium you’d get from nigari-coagulated tofu or a few drops in cooking water is modest. Nigari is not a substitute for a magnesium supplement if you have a diagnosed deficiency, but it does contribute meaningful trace minerals to food.
Other Culinary Uses
Beyond tofu, nigari has a small but growing following among home cooks. Some people add a few drops to rice cooking water or soups, claiming it enhances flavor and adds mineral content. In Japan, it’s sometimes added to drinking water in very small amounts as a mineral supplement. It can also be used as a firming agent for canned vegetables or as a flavor enhancer in certain fermented foods.
The key with all of these uses is dilution. Nigari straight from the bottle is intensely bitter and unpleasant. A little goes a long way.
Safety and Side Effects
Magnesium chloride is affirmed as “generally recognized as safe” (GRAS) by the FDA under food additive regulations. At the small quantities used in tofu making and cooking, nigari poses no health concerns for most people.
Concentrated nigari is a different story. Both magnesium chloride and magnesium sulfate act as osmotic laxatives, meaning they draw water into the intestines. Consuming too much can cause diarrhea, nausea, and abdominal cramping. At very high doses, excess magnesium can accumulate in the body and cause more serious effects: low blood pressure, muscle weakness, difficulty breathing, and irregular heartbeat. These effects are associated with pharmacological doses, not the small amounts used in food preparation, but they’re the reason you should treat nigari as a cooking ingredient rather than drinking it in large quantities.
People with kidney problems should be particularly cautious, since the kidneys are responsible for clearing excess magnesium from the body. When kidney function is compromised, magnesium can build up to levels that affect the heart and nervous system.
How to Buy and Store Nigari
Nigari is sold in two forms: liquid and dried flakes. Liquid nigari is the more traditional form and is ready to use, while flakes need to be dissolved in water before use. Both are available at Japanese grocery stores, health food stores, and online retailers. Look for food-grade nigari specifically labeled for tofu making or culinary use.
Liquid nigari keeps well at room temperature in a sealed container, and dried flakes have an essentially indefinite shelf life if kept dry. A small bottle will last a long time since most tofu recipes call for only one to two teaspoons of liquid nigari per batch.