Wednesday, February 1, 2012

Surface Area, Tea, Food, Physics: Do We Misuse The Word "Superficial"?

This post is about surface area, both as it pertains to tea, to food, and to everything about our world. In our culture, we use language in such a way that implies that, when dealing with anything, it's what's really inside that matters. Phrases like "on the surface", or the word "superficial" (which just means on the surface) are used to describe phenomena that are somehow more fleeting or transient, less reflective of true reality, and less important than things that are "deep", "on the inside", or "at the core" of something.

Diagram by Cmglee, used under CC BY-SA 3.0.

This post provides some powerful examples that demonstrate that this way of looking at things is not always valid. The world, both on a human level, and a fundamental physical level, does not always work in the way that the the word "superficial" suggests. The surface, or the boundary of a region, is often where the most interesting things are happening, and this phenomenon is widespread at all levels in our universe.

Surface and Boundary in Biology:

Anyone who has studied microbiology will undoubtedly be familiar with the cell membrane. Cell membranes, a double layer of nonpolar (oily) and polar (like water) substances creates a barrier which separates the interior of a cell from the outside world. Complex channels exist in these membranes to allow a living cell to control what passes through its walls, and structures attach to the membrane to allow it to interact with the outside world. A large portion of biological research focuses on the cell membrane or the various proteins and structures that exist within it.

Tea And Surface Area:

The surface area of tea leaf is of critical importance in determining how the tea infuses in water. The infusion of the tea's flavor and chemicals into the water happens at the surface of the leaf, so increasing the surface area will make the tea infuse more quickly.

The following is a photo of Imperial Tea Garden's Moon Swirl White Tip, a green tea from Hunan province. The complex curls and folds of the leaf provide greater surface area than the small, tightly rolled pellets suggest.

Breaking up the tea leaf increases the surface area, thus making the tea infuse faster. Finely-broken tea, like fannings and dust, have the highest surface area to volume ratio, and thus infuse fastest. On the other hand, whole-leaf tea with thick, tough leaves has the highest surface area to volume ratio, and thus infuses slowest of all, considerably slower than whole-leaf tea with thinner, more delicate leaves.

Thinking about surface area also helps us to understand the infusion behavior of flavored teas as compared to pure teas. When flavoring is added in the form of extracts or essential oils, the flavoring is added to the surface of the leaf. While some of the flavor may permeate deeper into the leaf, it is concentrated on the surface. The flavoring thus infuses very quickly. This is why flavored teas often have the strongest aroma of their "flavor" in the first infusion, and then taste more like tea in subsequent infusions.

Food, Surface Area, and Nutrition:

Surface area is relevant in food and nutrition as well. The skin of fruits and vegetables tend to be richer in vitamins, minerals, and proteins than the interior. Although not all fruit and vegetables have edible skin, the ones that do often have remarkably more nutritional value in their skin. As an example, let's look at the potato:

The USDA Nutrient Database tells us that 100 grams of baked potato skins have 4 grams of protein, 8 grams of fiber, and 39% RDA of Iron. 100 grams of baked potato flesh, on the other hand, while slightly less caloric (probably because they contain more water), only contains 2% of Iron, 2 grams of protein, and 1 gram of fiber. Baked potatos are not a good example for comparing Vitamin C content because the skin of the potato is exposed to more heat than the interior, so, although the skin is richer in Vitamin C, baked potato skins have similar vitamin C content. This is just an example. In some fruits, such as apples, the skin contains much more vitamin C by weight than the flesh. Moral of the story: don't peel your fruits and vegetables.

This blue potato has a lumpy shape, increasing its surface-area per unit volume. Buying lumpy, irregularly-shaped varieties of fruit can actually lead to better nutrition by adding more surface area. Similarly, buying small fruits also has the same effect.

Surface Area And Information in Quantum Physics:

There is some relatively recent work in quantum physics that has suggested a most peculiar result: it is possible that the amount of information that can be stored in a region of space is bounded not by its volume, but by its surface area. If you're a physicist, you can find the original paper here: Operational view of the holographic information bound, published in Physics Review D, Vol. 82, No. 12, 2010.

Doesn't it sound bizarre and counterintuitive? In other words, imagine a filing cabinet. The amount of information you can put in the cabinet depends not on the space inside the cabinet, but on the amount of area on the walls of the cabinet.

What does all this mean?

The point is...the phenomenon of the surface being more important than the inside of something, and the surface area being more important than volume for various practical reasons, is a phenomenon that appears again and again at all levels of our world: with tea, with food, with microbiology, and with the very fundamental laws of physics at the smallest possible scales.

So next time someone describes something as superficial, stop to think...maybe they're actually describing the things that really matter in life.


  1. I don't think that the idea of superficiality implies that the inside of something is more important than the outside, I think it's used to illustrate the idea that there's more to something than what you first see. The inside of something is more hidden - it's harder to get to, and it takes some effort or time to cut something open and see the inside of it. And I think the point the idea of superficiality is that you need to take the inside into account as well as the outside - to see someone as a whole person, and take the time to get to know them, not just make assumptions based on their external appearance.

  2. That makes sense. I think there is a lot of truth in our common use of the word "superficial" and the concept of it being worth looking beneath the surface or first impressions.

    I was just sharing this post to highlight some interesting cases where this analogy doesn't work as well! Both ways of looking at things are valid, and one or the other may be more relevant in certain situations.