This article covers how to prepare ingredients before making the best tempura batter. It is part of our series on making tempura.

The fundamental guiding principle behind the preparation of any ingredient is simple: to prepare ingredients in a manner that enables the chosen cooking method to showcase their finest qualities. Whether through the basic peeling & turning of root vegetables, to more elaborate techniques like tying, blanching & oblique cuts.

In this case, it’s important to bear in mind what tempura actually is- a type of deep frying where food is quickly cooked by completely submerging in hot oil. As such, ingredients for tempura should be prepared in a way which allows for the food to be cooked to your desired doneness in a short period of time. Furthermore, as the hot oil transforms the water within the ingredient into steam, any excess internal steam emitted from the food after removal from the oil will cause the tempura to go soggy. Therefore, ingredient preparation for tempura should aim to maximize the dehydration of the ingredients though frying. Balancing these two key ideas is crucial for making good tempura.

The key ideas to keep in mind are to:

1. Remove excess moisture or choose ingredients with a low moisture content
2. Maximize surface area to volume ratio by cutting ingredients thinly
3. Fry starchy ingredients at lower temperatures
4. Choose ingredients that fry well & do not absorb oil
5. Use starch to help batter to cling onto the ingredients

Fish
The first step to preparing any ingredient for tempura is to remove any excess moisture. This is mainly a problem for meat or seafood & less a problem for vegetables. Looking at fish as an example, most restaurants will always wrap their fish fillets in fish paper to absorb any excess moisture prior to frying.

The traditional choice of fish used in tempura is also limited to lean thin small fish with a low fat content. Fish that have a thin thickness have an extremely high surface area to volume ratio, allowing them to lose moisture quickly without overcooking at the same time.

In contrast, you rarely ever see fillets that are thick used in tempura as this is considered highly unsuitable. As the meat is thick, the appearance of the outer tempura crust can appear perfectly cooked while the inside remains under cooked. Additionally, oily fish with a high fat content are never used to fry tempura.

Vegetables
The same principles of ingredient preparation also apply to vegetables. Some vegetables naturally already contain a low moisture content & thus do not require as much processing such as fukinoto, mitsuba & shiso leaves. For other vegetables however, the surface area to volume ratio is usually maximized by cutting them thinly. For example, Lotus root & eggplant are cut into large but thin slices to maximize exposure to the oil. You’ll sometimes find baby eggplant cut into the highly recognisable fan shape.

Eggplant is actually a fantastic example of where ingredient choice & preparation can greatly affect frying outcome. In collaboration with farmers, some tempura restaurants specifically request eggplant that is slightly less ripe with greener flesh. Such eggplant has a much lower moisture content & firmer flesh, meaning that the resulting tempura crust will remain crispy for a much longer time, with the inner flesh not having a mushy texture. Some varieties of eggplant can also have a thick skin. In this case, small cuts or slits can be made on the skin to soften it during frying.

Starchy vegetables
The preparation of starchy vegetables is great to contrast how high quality tempura can be made by adjusting ingredient preparation & applying the same principles in different ways.

Even if cut thinly, root vegetables such as sweet potato & kabocha squash will still most likely burn on the outside before the inside is cooked through. And so instead, starch rich ingredients are sometimes cut as thick slices & cooked at a very low temperature. Cooking them at a lower temperature allows the thick starchy vegetables to steam through whilst also concentrating their flavour. It also allows sugars in the vegetables time to caramelize slightly, accentuating their sweetness. This way, enough moisture can be evaporated from the ingredients without it overcooking.

A unique example that falls into this category is asparagus. Whilst the tips of asparagus can be fried as tempura like any normal vegetables, tempura chef Niitome devised a special way to bring out the best flavour in different parts of the asparagus by separately cooking the lower end. As the lower end is tougher & contains more starch, he switches off his stove & cooks the asparagus end with the residual heat in the pot. By using such low heat, the asparagus has time to tenderize & cook though.

Other seafood
Again, frying seafood other than fish is all about controlling the moisture content. Seafood such as shrimp, scallops, clams & oysters are always blotted dry with paper towel or fish paper. This is particularly important for clams & oysters which can have a lot of internal moisture combined, with outer folds that can harbor moisture even after patting dry with paper towel. Seafood in the bivalve class are actually notorious among tempura chefs for causing the frying oil to splash & splutter from the amount of moisture they contain. As such, some chefs choose to apply a thicker than usual coating of potato starch over them before dipping them in batter.

For shrimp, a small cut is also made in the tail before being scraped with the knife to squeeze out excess water before the entire shrimp is dried with fish paper again.

For certain seafood, some chefs deliberately fry it just long enough for the outside to cook, leaving the inside still raw but just warmed through. The most notable example of this are scallops, with the idea being to allow the guest to enjoy the contrasting savory meaty outer layer with the sweet tender raw centre. Tempura cooked in this manner can still have a high moisture content & so much be served immediately.

Other specialty ingredients
Outside of Japan, one of the more innovative uses of tempura are courgette flowers stuffed with ricotta & Parma ham. The flower petals of courgette flowers themselves contain little to no moisture & are therefore perfect for tempura. They are the perfect vessel that can be used to encapsulate ricotta cheese which will melt from their own steam.

Starch
The application of starch should be done right before the ingredients are dipped into the batter as any earlier & any moisture on the surface of the ingredients can hydrate the starch, causing it to become sticky & alter the texture of the final crust.

Whether or not to apply starch to an ingredient before dipping it in batter is a decision made on a case by case basis by the chef. You’ll find that chefs at high end restaurants choose to apply starch selectively. Some apply it on mushrooms or fish, some choose not to. Some chefs choose to completely forgo the starch coating. At lower end restaurants where the emphasis is to wolf down an energy rich bowl of deep fried food rather than to slowly appreciate the seasonality of ingredients, it’s more standard to apply the starch coating to every single piece of ingredient as they’re placing more emphasis on consistency.

Please note that rice or potato scratch is interchangeable with rice or potato flour. We feel that the word ‘starch’ is more accurate as it doesn’t contain gluten. Rice & potato flour also doesn’t contain gluten & is the same product with a different name. If you can’t find these starches where you live, corn flour or corn starch can be used as a substitute.

If any kind of starch is not available, please do not coat ingredients with wheat flour of any kind as the gluten content will interfere with the batter & affect the mouthfeel of the final tempura crust.

What is the best flour for tempura
As traditional Japanese tempura batter only consists of water, eggs & flour, the specific qualities of each of these ingredients are extremely important. From our intensive testing that has been carried out, we have come to the conclusion that of these three ingredients, it is the selection of flour that has one of the greatest impacts on your final tempura. Therefore, we wanted to dive deep into what sort of flour you should be looking for when trying to make tempura.

In a tempura batter, the flour used has the greatest influence over the final texture of the batter. As the batter primarily serves as the textural complement to the burst of flavour from the actual tempura ingredients themselves, the batter itself tends to be fairly subtle in flavour with maybe a light hint of umami & aroma absorbed from the frying oil. Therefore, the customary flour used for making tempura batter is your standard neutral flavored wheat flour. Other flours such as rye, buckwheat, & semolina etc are almost never used due to their coarser texture & more pronounced taste.

Why is gluten development in tempura important?
The gluten development in a batter or dough, or the lack thereof, gives many of the foods we encounter daily their characteristic taste. When making pies, tarts & shortbread cookies, having as little gluten development as possible is paramount to obtain a crumbly & melt in your mouth texture. Too much gluten development & your cookies will be hard & chewy.

The opposite is true for bread & pasta. A well developed gluten network is what gives bread their characteristic chewy texture, while also allowing pasta dough to be rolled thin & stretch out into longstrands without tearing or breaking apart, giving them that sought after al-dente texture when bitten into. If too little gluten development is achieved, bread dough will collapse in the oven when baked, whilst noodles will fall apart when boiled, becoming soft & mushy

Unfortunately for us, great tempura batter lies not at either ends of the gluten development spectrum, but somewhere in between, within a goldilocks zone that tempura chefs are forever striving to stay within.

If too much gluten development occurs, there are two usual resulting scenarios:

1. your tempura batter may still be crispy straight out of the fryer, but will quickly become soggy by the time it’s served to your guest.

2. Your tempura batter is hard & crunchy rather than lightly & crispy, much like the crust you’d find on fish & chips rather than tempura.

3. The opposite end of the spectrum, where too little gluten development occurs, is more subtle yet still noticeable. Your resulting tempura might still be light, crispy & airy but once you bite into it you’ll realize that the batter doesn’t melt in your mouth. Instead, the batter is slightly jagged & brittle, shattering in your mouth as though there is no structure.

What is the ideal amount of gluten development in tempura batter?
Instead, if the ideal amount of gluten development in your batter is achieved, the resulting tempura will have thin sheets or flakes of batter surrounding the ingredients. The flakes should be thin enough to let light through, yet strong enough to withstand being fished out of the oil without breaking. It is these laces of tempura batter that should be delicately crispy at the first bite, before lightly melting away in your mouth.

The science behind Michelin quality tempura batter
*We recommend reading our article on how to choose the best flour for tempura first. All the information mentioned in this article is incorporated into our ultimately tempura batter technique. Otherwise, have a look at our tempura series.

Mentioned in our primer on gluten, whilst the formation of your tempura batter’s gluten network will continue to occur spontaneously after the flour is hydrated, it will continue to do so slowly. However, this process can be sped up by mixing the batter. This can be seen in bread, where bread dough is typically mixed & kneaded to increase the rate of gluten development. Bread doughs mixed in machines can reach their required gluten development after 10-15 minutes of mechanical mixing, whilst the same amount of gluten development in a dough simply left to its own devices might require 12 to 24 hours of waiting.

Beyond developing a batter’s gluten network, the role of mixing also influences two important variables: how homogeneously combined the batter ingredients are, & how evenly the flour is hydrated. Whilst these two variables do have an effect on the quality of tempura produced, they have a much larger impact on maintaining the consistency between different batches of tempura batter.

Why should we keep our tempura batter cold?
In our article on the science of koji, we elaborated on how temperature affects the rate of enzyme reactions. Whilst we talked specifically about the enzymes produced by koji, the explanations are still relevant here. This is because as mentioned in our primer on gluten, the formation of a gluten network in our tempura batter is due to two chemical processes running simultaneously together: the linking of glutenin & gliadin proteins, as well as the action of proteases naturally present in the flour.

As the rate of chemical reactions slows at lower temperatures, if we were to lower the temperature of the batter, it’s then possible to slow down the natural formation of gluten over time. This allows us to maintain our tempura batter at its peak state for a longer period of time, reducing the need to make new batches of tempura so frequently.

How do we keep our tempura batter cold?
Tempura batter at a specialty restaurant is typically kept cold using 3 basic techniques:

1. Storing your tempura flour in the freezer (read tempura niitome’s recipe)
2. Making your tempura batter with cold water
3. Keeping your tempura batter bowl in the fridge prior to use.
4. Some chefs advocate the use of cold sparkling water when making tempura batter which is elaborated on in our article on tempura additives.

Making tempura batter as close to frying as possible
As our modern technique for making tempura batter requires us to whisk the batter until the optimal amount of gluten development is reached, the batter therefore starts to deteriorate from the moment of its creation. As such, it’s of utmost importance that you make your batter as close as possible to when you start frying. Experience chefs typically heat their oil to just the right temperature before quickly whisking together their batter. We recommend following the same advice where you have your ingredients prepared & oil heating up before you make your batter.

The ultimate tempura batter technique
The science behind the technique below is elaborated in our article on how to make the best tempura batter, & can be followed up with how to maintain your tempura batter. These articles are part of our tempura series.