Introduction: An Illustrated Guide to the Science of Mochi
How many times have you been desperate for a quick, easy dish to take to your next science fair/international food festival? All the time right? Enter "An Illustrated Guide To The Science of Mochi." The answer to all your prayers. (note, this is also really fun to make with kids. They absolutely love the sweet mochi and the science that goes into it!)
If you haven't heard of mochi, I'm sorry. It's wonderful.
Mochi is a kind of squishy Asian rice candy, (there's some debate about whether it originated in Taiwan, China, or Japan, but there's no debate that it's delicious.) It's super easy to make and there are literally thousands of possibilities for flavoring, but perhaps the best thing about mochi is the weird, wacky, wonderful science that goes into making it!
Step 2: How It Works
Okay, remember how I said that mochi was a rice candy? Well, that's not necessarily always true. Technically it can also be made with potato starch, arrowroot flour, sago starch, or tapioca starch. However rice, namely short-grain rice, is still by far the most popular method. Here's why.
Starches are made up of two base components: Amylopectin and amylose. Medium and long grain rices, which can't be used for mochi, are made up of mostly amylose. But short grain rice as well as all of the starches listed above are made up of primarily Amylopectin. Amylopectin is is much more hygroscopic than amylose, which for people who didn't major in chemistry means that Amylopectin absorbs more water. Mochi in its simplest form is just a chewy elastic dough made from fully hydrated Amylopectin.
You might ask, "If all those other starches can make mochi, why is 99% of mochi still made with rice?" The answer to that question lies in both the geography where mochi was created and the chemistry of how it's made. When mochi was created in approximately 100 A.D. rice was a staple in Asia, and grew well in the climate, as such traditional mochi is made with rice. In addition to this, rice flour is still one of the most concentrated sources of Amylopectin and when ground into a fine powder, (called shiratamako,) it produces the best, (and stretchiest,) mochi.
Step 3: How to Make It
So now that we've covered the most important part of the science of mochi, it's time for you to try making it yourself. Since the Amylopectin absorbs pretty much any water-like fluid like tea, juice, milk, liquor, etc... and some oils too, the flavoring possibilities are endless. I encourage you to experiment on your own and find your preferred choice of flavoring, but I'm going to draw up a nice strawberry flavor. You will need:
- A large glass bowl
- Mochiko rice flour 1 1/4 cups (also called glutinous rice flour. Do not get ordinary rice flour, it will not work. Remember the Amylopectin and check your local international market if your grocery store doesn't stock it.)
- Your chosen liquid/flavoring. I'm using a mix of 1.5 cups of coconut milk and 1/2 a cup strawberry puree and 1/2 a teaspoon vanilla
- Sugar 3/4 a cup
- Baking Powder 1/2 a teaspoon
- cooking spray
- Potato starch (for dusting)
- glass or ceramic pan
- Plastic wrap
First: In the glass bowl mix all the wet flavoring ingredients, the baking powder, and the sugar. slowly mix in the rice flour until smooth. Cover the bowl with plastic wrap leaving one small hole for vapor and heated air to escape from.
Microwaves work by zapping their contents with, well... Microwaves. Microwaves are the shortest type of radio wave, (side-note, these are also the types of waves that your cellphone uses to transmit your voice,) and when these waves go through your food, they make the molecules move much faster. generating heat. When the mixture is heated, two things will happen. First, the Amylopectin will begin absorbing the liquid more readily and the mochi mixture will start to thicken. Secondly, the leavening agent, (baking powder,) which is only necessary in the microwave recipe as the traditional way of making it gives it time to form air pockets on it's own, will release small bubbles of gas into the mochi, expanding it.
Microwave your mochi for 5 minutes, than remove and stir. This will give you an excellent opportunity to observe the chemistry in action as it will have already gotten thicker and more elastic! Pop it back in the microwave for five more minutes and than stir it again. Grease your pan and then pour the mochi mixture into it, then wrap it in plastic wrap and stick it in the fridge. This will slow down the movement of the molecules in the mix making it more solid.
Step 4: Final Prep and Why Mochi Is Sticky
You can do a lot of things with your mochi like fill it with ice cream or red bean paste, chop it up and sprinkle it on your frozen yogurt, or sculpt it into a cute shape with your fingers or a cookie cutter. But I prefer to just cut it up and eat it.
To do this, dust a cutting board liberally with corn starch and overturn the pan of solidified mochi over it. Cut it into small squares with a knife and dust these in more cornstarch to prevent the mochi from sticking to you and everything you own. If you're wondering why it's so sticky the answer is the same as why most common glues are sticky: the molecules in the mochi are forming weak hydrogen bonds with everything they touch, even your skin! Cool, right?
And there you have it. The science behind mochi, a dish that is perfect for your next chemistry class party/international food festival, and a delicious topping, and perfect movie snack. I hope you enjoyed this illustrated instructable and if you have any questions regarding the preparation or chemistry of this dessert, feel free to ask me in the comments and I would be happy to help! If you like this instructable, please vote for it in the food science contest!
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Science of Cooking
1 year ago
Hi, may i also know whether steaming the mochi using the stove top or microwave will it make any difference to the texture or elasticity of the mochi:) thank you!
Reply 1 year ago
Possibly, although I doubt it will make enough difference to really tell. This question is where we've reached the limits of my knowledge. 😅
1 year ago on Step 4
hii may I know how gelatinization is involved in mochi making and at which part of the mochi making process does it occur. Also, how does the hydrogen bond thing stick to everything is there a science behind it? thank u
Reply 1 year ago
It's a fairly thick liquid, but it's not really gelatinous until you cook it. Also hydrogen bonds are an electrostatic bond between hydrogen and primarily second-row elements on the periodic table like oxygen, nitrogen, etc.. How sticky it is to a particular surface will depend partially on the molecular composition, but mostly on other attributes like texture, temperature, moisture, etc... 😁
Question 2 years ago
How does corn starch cause mochi to stop sticking to surfaces?
Answer 2 years ago
It bonds to the surface so nothing else can and since it's a fine power it's able to cover the whole thing. Corn starch is best because it doesn't have much flavor and doesn't come with the risks that eating raw flour does. 👍
Question 2 years ago on Introduction
Hii, i'm currently thinking of developing certain type of mochi. I wish to make it more sugar-free and healthier as i wanted to use mucilage from certain plants. Do you think it is possible to substitute the water source with mucilage ? And are there any type of starch that could possibly be the substitution to the glutinous rice flour but still gave good mochi results ? Thankyou so much ! I really like how you manage to explaine amylopectin so easily !
Answer 2 years ago
Hello! I'm glad you liked my Instructable! The answer to your question is complicated and requires some explanation. First of all, yes, I think mucilage should absorb into the starch well. But you may not get the results you're hoping for. The thing about all amylopectin is that it decreases your insulin response to sugars. This means that there will be a higher concentration of consumed sugars in your bloodstream, effectively making sugar have more of an impact on your body. This is fine in balanced diets but plant mucilages are polysacharides, which means they are made of large sugar molecules and acids, and therefore increase the amount of overall sugar. Note that this does not mean that mucilage is unhealthy or sugary. The polysacharides in mucilage are much more complex than the simple sugars found in processed foods and therefore take longer for your body to break down which lessens the impact and is a great way to eat the necessary sugars for your diet. But if you want a healthier version of the mochi my advice would be to try a fermented beverage where the sugars will have been consumed, like kombucha. A plant puree may work as well because while it will still contain sugars it will also contain nutrients and flavors from the plant tissue. You may have to experiment with ratios to replace the lost volume from eliminating the added sugar but please keep me updated on your progress!