The One Ingredient That Makes Fried Food Taste Even Better—and It’s Already in Your Fridge

Have you ever wondered how restaurants get their fried food so crispy? Things like tempura-battered vegetables and shrimp are obviously deep-fried; their crunchy exterior can attest to that. Yet the outer coating is also light, airy, and not overly heavy like many fried foods. It all comes down to one special ingredient in the batter—sparkling water. You probably already have some form of sparkling water on hand, and if not, you can find it at every supermarket or corner store—and it’s time you started incorporating it into your deep-fried foods. We spoke to a food scientist who explains why sparkling water makes such a difference to fry batter.

The Science Behind Carbonation

What is it about sparkling water that transforms a heavy battered food into something as light as air? The answer has to do with carbonation. According to food scientist Bryan Quoc Le, Ph.D., sparkling water is carbonated to contain high concentrations of carbon dioxide. Most of this carbon dioxide is in the form of carbonic acid, which happens when it combines with water at a high pressure. However, carbonic acid is relatively unstable and breaks down into carbon dioxide and water at room temperature. This is exactly what happens when you open a can of soda and leave it at room temperature–it becomes flat. 

“At higher temperatures, especially those found during frying, the carbon dioxide is released even more rapidly,” he says. This rapid decomposition of carbonic acid into carbon dioxide causes very fine bubbles to form in the batter. Those bubbles are then solidified by the frying process, which is why batters with sparkling water stay so light and crisp.

Sparkling Water vs. Club Soda vs. Soda Water

Quoc Le explains that while similar, sparkling water, club soda, and soda water all contain different concentrations of minerals. This depends entirely on the source or added minerals each water manufacturer uses. Some minerals added to the water are more alkaline than others or contain more alkali earth metals, such as calcium or magnesium. These can directly influence the amount of carbon dioxide that the water holds. Additionally, it can affect the overall flavor and texture of the batter and, therefore, the fried food. A higher carbon dioxide capacity means finer bubbles and a more aerated batter. 

In terms of flavor, the water's mineral makeup is important. Calcium, potassium, and magnesium minerals can give the batter a more metallic taste, whereas sodium salts can reduce the bitterness that’s usually found to some extent in sparkling water. More alkaline minerals like these help neutralize acids in the batter, leaving the fried food with a very pleasant flavor. That’s why we usually reach for sparkling water for the batter—it’s more neutral than club soda or soda water.

How to Use Sparkling Water in Fried Food

A basic tempura batter is made with simple ingredients, including egg yolks, flour, and cold sparkling water. 

• Egg yolks: Since the aeration in this batter comes from the sparkling water, you don’t need to use egg whites. Instead, the yolks are mixed into the batter. The yolks are high in fat, which helps emulsify the batter and add structure. Store unused egg whites in an airtight container in the freezer for up to 1 month, and use them later to make a pavlova or a batch of macaroons. 
• Flour: Regular all-purpose flour will work here, but for the lightest batter imaginable, we like to use cake or pastry flour. Cake flour has a lower gluten content, so the batter remains delicate instead of getting tough in the fryer. 
• Sparkling water: The magic ingredient—the most important thing is to keep the sparkling water cold before mixing it into the batter. 

To make a fry batter using sparkling water, you’ll want to keep some of the cake flour separate in a shallow dish. The rest of the flour gets whisked in a bowl with the egg yolks and sparkling water until it’s mostly combined with a few lumps still remaining–you don’t want to overmix the batter. The battered food usually takes about 3 minutes to cook in a large pot of 350-degree Fahrenheit oil.

What Kind of Foods to Fry

Tempura batter is used mostly on fish and vegetables. 

• Fish: The most important thing is to choose pieces of fish that will cook pretty quickly. Shrimp is the most popular option, as it cooks in just a few minutes. Cubes of tender whitefish, such as sea bass, halibut, or cod also cook in no time. You can serve any of these fried fish options on a platter with some dipping sauces, such as spicy mayonnaise, soy sauce, or black vinegar. They are also delicious piled into fish tacos with a nice vinegar-based coleslaw on top. 
• Vegetables: Any and all vegetables can be used here, from the most delicate to the more starchy varieties. Try starchy vegetables like sweet potatoes and pumpkin; delicate summer squash and eggplant; hearty broccoli and cauliflower florets; delicate snap peas, snow peas, and miniature shishito and padron peppers; or a mix of wild mushrooms, such as oyster and maitake.