Zongzi, mochi, and mango sticky rice (credit: Eastday, Wikipedia, Rasamalaysia)
Glutinous rice, also known as sticky rice, is a type of widely cultivated rice in Asia. It is of great significance in Asian cuisines. There are tons of delicious food made from sticky rice. If you have not tried sticky rice, you are missing out!
Starch is the major component in rice. There are two types of polymer molecules in starch: amylose and amylopectin. They differ by the connectivity between glucose building blocks. Amylose is more crystallizable and insoluble in water due to its linear chain. Amylopectin, on the other hand, is branched and water soluble.
When we cook rice in hot water, the water molecules can get between the polymer chains in starch and loosen up the tightly packed polymers (it is called plasticizing effect). This makes the rice softer and stickier upon cooking. The relative amounts of amylose and amylopectin in starch can significantly affect the texture of cooked rice. For example, long-grain rice has high amylose content, making it less penetrable by water and therefore less sticky; glutinous rice has negligible amount of amylose and very high amylopectin content, which results in strong plasticizing effect that leads to the sticky texture.
The origin of sticky rice has been investigated. Scientists have identified a genetic mutation that leads to the disruption of amylose synthesis in sticky rise. This mutation likely arose from a single evolutionary origin in Southeast Asia.
Clarifying liquids is a common culinary technique that is used to make things like consommé (a type of soup made from clarifying stock). Traditionally, French chefs used a complicated egg-white technique, but people in recent years have come up with improved techniques. We found this paper by Jacob B. Lahne and Shelly J. Schmidt, sharing an experiment of clarifying fruit juice using gelation (what’s in Jello). A lot of people have gelatin powder in their kitchens– it’s useful for making all kinds of desserts and sold in any grocery store. All you need is a bit of gelatin and some fruit juice, and you can harness the science of this freeze concentration process to make your own purified, flavor-packed fruit juice.
Here’s what you’ll need:
1/2 teaspoon of gelatin powder
3-5 teaspoons of hot water
1 cup fruit juice (something cloudy like orange juice or grapefruit juice)
First, dissolve the gelatin powder in the hot water by vigorously stirring. If you have difficult dissolving (the gelatin and water will become really sticky when the gelatin is too concentrated), you can microwave it briefly in 10 second increments. Once it is dissolve, whisk it into the fruit juice and mix completely. Pour into a container and freeze completely. As a control to help see the role of the gelatin, we also suggest you freeze plain juice without gelatin.
When this mixture is freezing, it undergoes a freeze concentration process that drives the particulates out from water as it freezes into a solid, since these particulates are less soluble in ice than in liquid water (Figure A&B). These particulates include larger sized ones like gelatin and cloudiness-causing particles, as well as smaller ones like most of the ones responsible for taste and aroma. During this freeze concentration process, gelatin gets concentrated and starts to form a polymer network (Figure B). This network is responsible for why high concentrations of gelatin in water are so tacky and difficult to mix. When you let this frozen mixture come back to room temperature, the network also acts like a trap or a mesh, keeping in the larger particles responsible for cloudiness, while letting the smaller aroma-contributing particles dissolve in the melting water and come out (Figure C&D).
I tried this myself, and it was really simple to basically create my own jello filter to isolate the flavor in juice.
After letting both our juice/gelatin mixture and our juice-only control melt over filters back at room temperature, we noticed that a lot less liquid was collecting from the juice/gelatin one, since a lot of water was being trapped in the jello-like hydrogel that was sitting on the filter. This is the gelatin hydrogel that has formed during the freeze concentration process. On the other hand, after a long enough time, the juice-only cubes completely melted.
There was a clear color difference between our juice/gelatin and juice-only samples, with the juice/gelatin process producing a really clear liquid.
We also wanted to see that the flavor particles were really small enough to escape the gelatin filter, so we did a taste test. Sure enough, there was a lot of flavor in the clear juice. The taste was a little different from the control, and we also noticed that there was some orange flavor to the jelly that we were collecting the clear liquid from, so it seems like some flavor particles still got trapped in the gelatin hydrogel.
Do you know Ginger? The spice, not the British Pop Singer.
As a spice, ginger tastes zingy and spicy. It is the central ingredient of various delicious foods – gingerbread, ginger beer, and ginger ale are quite common in America, while in Indian and East Asian cuisine, it is one of the core spices added to various drinks, curries, soups, stir fries, etc.
What many don’t know is that ginger can also be cooked with milk! Mixing hot milk with ginger juice will get you the signature Cantonese dessert Ginger Hit Milk (姜撞奶), a simple two ingredient milk pudding.
So what makes Ginger so magical? Ginger has a special enzyme in it called Zingipain (sounds like Zingy Pain) that can break down protein quickly.
Why is the enzyme named Zingipain? Because it is the reason behind ginger tasting spicy and zingy on your tongue. Zingipain breaks down proteins on your tongue, causing you to feel the zingy pain. (Ok, that’s a lie, but it’s a good way to remember the name)
So what happen when Zingipain from the ginger encounters milk protein? It actually breaks down the milk protein as well. But why does that make your milk curd into pudding?
Turns out that milk is not just a white-out from cow, its a colloid suspension of milk proteins in water.
Do most protein like water? Not necessary. Some proteins do and some do not.
What happens to the proteins that don’t like water? They hide under the cover of proteins that like the water.
When Zingipain from the ginger meet the milk protein, it starts to break down the outer shell of proteins (the ones that like water, hydrophilic ), and leaving the cores (the ones that hate water, hydrophobic) exposed to water.
What do protein do when they are suddenly exposed in a environment that they don’t like? They bundle up and connect to each other, which is why the milk starts to curd and turns from liquid to solid.
Will Ginger curd milk at any temperature?
Zingipain, as well as any other protein enzyme, is sensitive to temperature. It won’t be activated at low temperature, and it can be damaged and denatured at high temperature. Here is a simple experiment you can do at home to showcase that.
Prepare three glass of milk (frozen, 50 ˚C and 80 ˚C), and add the ginger juice to it, and see which glass of milk turn into pudding in the end. You can judge for yourself at which temperature is zingipain most active.
Across the country, shelter-in-place orders are being lifted, but wearing a mask in public has become a part of life. Is the mask you wear really that good at keeping the virus away, and why it is important that we all wear masks?
There are many types of mask on the market. The N95 worn by the front line health workers, the Guy Fawkes V for Vendetta mask worn by some protesters, the cloth mask coming in a pack of three, the ski mask with a hole in the mouth, and the plague doctor mask from your Halloween costume. They are all valid options on amazon, but only some of the choices make sense.
Are all masks created equal? Sadly not. But you already know that.
Pedantically, there is a distinction between surgical masks and N95 respirators. In short, a respirator protects the people wearing it, while a mask protects the people around the person who is wearing it. Here, in this chart, I’ve listed out the major difference between masks and respirators.
A N95 respirator is defined as >95% blockage of incoming 300 nm particles. (If you are wondering why 300 nm matters, you can read one of our previous blog The magic of N95 mask. )
Unlike a respirator, a mask is not very effective at blocking in coming particle to the person wearing the mask. Don’t just take my word for it. This paper in 2013 measured and compared the filtering efficacy and leakage of common brand of N95 and surgical mask, and they found that N95 masks has lower than 2% particle making through the mask (penetration), and lower than 3% particles leaked from the sides, while a surgical mask can have up to 20% particle penetration and 40% leakage.
So, maybe surgical masks are not as effective as you think? How about a cloth mask then? In this other study in 2013, the author examined two layer common household fabrics, and he found that most of them have around 70% success rate at blocking particle penetration, while two layers of surgical mask can achieve 96% success rate.
Based on these study, we can conclude that neither surgical mask nor cloth mask is effective at blocking in-coming particles. So why is wearing face mask still helpful?
The answer is that it is helpful if everyone is wearing a mask. Although basic masks cannot effectively block in-coming particles, they are still effective at blocking spit droplets of the person wearing the mask from flying into the air. Essentially, you protect other people by wearing a mask, and other people do the same to you.
Respect to the front line health workers, and go wear a mask.
It takes some skill to be able to pick up a single grain of rice with a pair of chopsticks…. but can you pick up a whole container of rice with just a single chopstick?
If you just pour rice into a container and stick a chopstick into it, what happens is just about what you’d expect:
But if you compact the rice by tapping the container on the counter a few times, you can fill the same volume up with a lot more rice. Something surprising then happens when you stick a chopstick in:
The difference between these two cases is the density of the rice. In the first case, there are a lot of air pockets between the loosely-packed rice grains. In the second case, there is a lot more friction between the more densely-packed particles.
Friction is a force resisting the motion of one object’s surface against another’s. When the rice is so densely packed, there is enough friction between the rice grains and the chopstick that the chopstick can be held in place–allowing you to pick up the whole container!
Have you ever put a plastic water bottle in your dishwasher and ended up with a miniature version? Were you wondering what kind of voodoo was going on in your dishwasher? Today, the Big Nano will show you how plastic bottles are made and why they shrink in the dishwasher.
The manufacturing of plastic bottles are very much similar to blowing up a balloon. First, preforms are made by injection molding process. Plastic materials and additives (dyes, plasticizers) are melted and well mixed together. The hot melt is then injected into a mold (often in cylindrical shape) and is cooled to produce preforms.
Next, the preforms are made into desired shapes by blow molding process. The preforms are heated to provide enough mobility to the polymer chains. Then, the heated preforms are clammed into a mold. Air is blown into the preforms to expand them into the shape of the mold. This is very much similar to blowing up a balloon. The plastic bottles are then cooled and their final shape is maintained at room temperatures.
If you look closely at a plastic container, you can find evidence of this two-step manufacturing process. For example, the bottom of this water bottle has an irregularly-shaped “button”. This is due to the way the preform was cut during the injection molding process.
A lot of the plastic bottles are not heat resistant. If you unfortunately put one of these bottles into your dishwasher, you will end up with a miniature bottle. This is because the polymer chains are under stress after the blow molding process. At room temperature, these polymer chains are “frozen” in place and the shape of the bottle is retained. However, at high temperature inside the dishwasher, the polymer chains are mobile enough. As they try to relax back into their original state, the plastic bottle starts to reverse back towards its original shape from the injection molding process.
We all know candies are made from sugar, but have you thought about how exactly they are made? In this edition of Overcooked COVID19, we will look at two sugar bars that can be simply made at home.
Rock candy recipe: Prepare a ton of sugar (yes, a ton), water, a pan, and some glass jars. Dissolve sugar in water. Heat up the solution and cool it down in the glass jar. Voila! Here is your rock candy. Didn’t get that recipe? Here is the fool-proof video tutorial,
Not your cup of sugar water? Then a bit of extra corn starch in the sugar water will turn your rock candy into a sugar glass. It is translucent, breakable, and edible.
So what happened? And what is the corn starch doing in the sugar glass?
Table sugars are composed of sucrose. As the hot sugar water cools down, sucrose is supersaturated in the solution and crystallizes through a process called nucleation-and-growth. In the video, the sugar on the string served as nucleation sites where rock-like sugar crystals started to grow.
Now what if we add in some corn starch that contains high molecular weight carbohydrate chains? Mixing molecules of different sizes prevents the sucrose from crystallization. As the sugar water cools down, the solution is forced to solidify but the molecules stayed in their liquid-like conformations, and hence the glassy state. Fun fact: glass is actually a liquid but it flows on a much longer time scale. Old glass windows are thinner on the top as the glass flows down by gravity over the years.
The crystallization process of sucrose happens really, really slow (did I forget to mention that rock candy takes ~ two weeks to form?). On the other hand, fast cooling is the key to glass formation. Extremely fast cooling can even turn metals into glass!
Now it’s time for extra credits: why is the heated sugar water brown? [Hint: That color reminds me of caramel…]