Making tapioca is a slightly involved process, though it really makes sense when you think of it in terms of what it really is: a kind of cassava starch pasta.
Starting with the pure cassava starch that I talked about in the previous post, the starch is moistened slightly and put into large rotating pans, not unlike the kind used to coat candies like M&M’s. The granules are simply rolled over and over onto one another until they start to collect in little balls or “pearls”. Just how big the pearls get is a factor of how long the panning process goes on.
At that point the pearls are steamed, causing the outer 50% of the starch molecules in the ball to gelate, or loosen and disperse among the water that collects on the pearl as it’s steamed. Here the gelating process is stopped and the pearls are dried, which causes something rather interesting to happen. The starch tries to “retrograde”, or revert back to its previous form, but just like an unbundled bale of hay, it’ll never fully go back to its once-compact form. Still, the molecules start re-bonding to each other, only this time they do it in a much more orderly fashion that they originally did, forming networks that are almost crystalline in their regularity. Being so orderly and tightly bound, these structures resist dispersal, even in boiling in water, which means they act like a skin, keeping the ball in one piece when it’s cooked.
It’s the very same process that’s employed to produce other types of all-starch (zero-protein) noodles like Japanese harusame, or “glass” noodles. Interesting, isn’t it, that both glass noodles and tapioca are more-or-less see-through. That’s because protein molecules scatter light rays, rendering wheat-based pastas opaque. But no protein means no scattered light, it just passes straight on through. Which is another way of saying: transparency.