I purchased some cod for the fillets of fish. The batter is amazingly crispy, unlike any I had used before. This is owed to the alcohol content, which evaporates quickly. Using beer and vodka instead of water. On top of this, additional bubbles of carbon dioxide are added using an iSi siphon with a soda charge. The fish itself is cooked perfectly to a moist and flaky texture. The fish was seasoned with salt, pepper, garlic powder, and cayenne, then covered with a batter of 50/50 AP flour/Rice flour. Fried at 425 F, the fillets only take a few minutes to cook through and brown.
The chips are crispy on the exterior, fluffy on the interior, and seasoned with salt and pepper. Great with some mayo and malt vinegar. The fries are first cut and boiled gently to cook through and rough up the edges. Cooked to just before they fall apart, the cracks allow oil to crisp up the exterior. Allowed to cool and dehydrate in the fridge for 30 minutes, they're cooked in relatively cool oil of 250-275 F until they take on a little bit of color. Then, they are allowed to dry and cool in the fridge for 30 minutes again. The final fry at 375 F gives them their golden color and crispy texture.
In More Depth
Batters and dough share much in common. Both have the core ingredients of flour and water. How are they different? Clearly, batters have far more water than doughs. What effect does this have? To understand this, we look at why we use flour in the first place. As you might already know, most of the flours we use for bread and batters come from wheat, so I'll focus on that.
The principal chemicals in flour we take advantage of are starches (carbohydrates) and gluten (proteins). When we make bread, we want the protein to develop a tight structure that traps the starch and water like a finely woven net. This is why we knead the bread until it achieves an elastic texture and allow it to rest. When yeast is added, this gluten structure traps the gas, which produces the bubbles that give some breads its airy texture. When mixing batters, such as those to coat foods like the fish above, or for pound cake, we only mix to just incorporate the flour. The gluten is secondary, helping to hold the mix together when it is cooked. In batters, the starch plays the starring role.
Starch, according to the Oxford English Dictionary, comes from a 15th century Dutch word that means to stiffen (sterche). Starch molecules come in a crystalline form, appearing as granules that absorb water, helping to thicken the liquid. This is why we use flour to make slurries, roux, and to thicken sauces. The starches swell up and stick to each other, creating the tender structure we like in batter cakes and coatings for fried foods. So, in Heston's recipe, we use some all-purpose flour, which has some gluten, but we also use a starch flour without gluten, the rice flour.
So, why does Heston's recipe call for injecting more bubbles in addition to those given by the beer? The answer lies in the leavening of the bubbles. According to Harold McGee the bubbles, "...not only divides [the batter] into innumerable thin sheets surrounding the gas bubbles, it makes the batter more viscous." (more viscosity = thicker). This does two things for our fried fish. First, the additional viscosity helps the batter stick to the food. Second, the layers allow the outside to cook quickly, releasing the water and browning. Since water boils at 212 F, we need to get rid of it to promote browning and crisping, which occurs at higher temperatures.
There is much more science going on here in this simple, but delicious dish. This is one of the exciting things about cooking: endless variety and depth. As we promote understanding, we enjoy cooking more, and can use the principles we learn to create new variation and improvements in existing foods.
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