For rice it depends. Cooking any starch in water will first cause the starch granules to swell and eventually tangle up with each other (the gelatinization). Dissolving sugars or salts in the water slows down the process by raising the temperature the swelling starts. While few prefer pasta as a stuck blob of strands, the same is not the case for rice. I like my Basmati loose, but my risotto and sushi sticky, so salt may be required for Basmati and optional for Arborio.
There are many techniques for controlling the starch for rice. To control the starch gelatinization of rice:
- cook it like pasta with lots of water, then drain; or
- par cook it
Method 1 won't avoid the grain surface starch gelatinization, but it will help with stickiness (you may oil coat it after draining). Method 2 delays the starch release allowing you to finish a risotto in seven minutes. Cool for parties or for restaurants.
Interesting question. Did search 'how do I make puffed rice'. Came up with some interesting information.
There are some writings that suggest that puffed rice can be made like popcorn; get the moisture in the grains of rice to the correct level (no idea what the level should be, experimentation should guide you I suppose) and then (depending on what source you read) put in a popcorn popper, put it on sheets in the oven or fry it in oil.
The history indicates that the first puffed rice made in the U.S. was actually shot from a cannon, after, I presume, being thoroughly soaked to some level of softness; there was a cereal advert in the '60s that bragged "this is the cereal that's shot from guns". Am thinking that the softening of the rice, probably by cooking, and then putting it into a pressure vessel in which the pressure is allowed to rise to a certain PSI (pounds per square inch) and explosively releasing the pressure, causes the grains to boil or fizz or effervesce, gives them the light puffiness we see at the market.
If I'm reading the information correctly, the devices to make puffed rice are available
Here is a link to a video showing the explosive creation of puffed rice by a traveling puffed rice manufactury on a bicycle in Taiwan;
http://video.google.com/videoplay?docid=-3915559836111131480#docid=-4928826327589404249
Here are some other links, kind of vague, regarding non explosive puffed rice:
http://recipes.howstuffworks.com/question393.htm
http://www.cheftalk.com/t/20752/how-to-make-puffed-rice
http://www.indiamike.com/india/indian-recipes-f108/how-to-make-puffed-rice-at-home-t94003/
This last link has some history & speculation of how puffed rice has been made non explosively using hot salt, or sand...didn't read all of the ideas.
Have fun, and be safe.
Best Answer
Starch is composed of two polymers (linked chains) of glucose (sugar): Amylopectin and Amylose. Amylopectin is a branched and much larger molecule than Amylose.
Starch molecules in a grain of rice are actually arranged in a semi-crystalline state. The granules are about 2μm in size in rice (different plants have different granule sizes).
Starch becomes soluble in water when heated. The granules swell and burst, the semi-crystalline state is lost, and the smaller amylose molecules leach out and form a network that holds water. Although the network of molecules holds water, it will of course have a larger volume than the volume of neatly-aligned molecules plus water. This process is called gelatinization.
So you can imagine that in a dry rice grain, the strands of starch are like the fairly neatly stacked threads in my T-shirt, some shorter, some longer branched nets. As you heat it, the threads get moving and tangled up, absorbing the water, but also expanding even more in size like that big mess of lint in my clothes drier.
A similar process happens with popping corn, except the water is contained in the kernel of corn and not added. It's quite apparent to see how much larger the volume of a bowl of popped corn is compared to the small package of unpopped corn with water inside.