Tag Archives: cooking

Food and science: Why are peppers hot?

Chili peppers, such as jalapeños and serranos and habañeros, are hot because they contain a chemical called capsaicin, which is an irritant to humans.

Why capsaicin?

If it is advantageous to plants to spread their seeds, why do the fruits (peppers) contain a chemical that repels animals? It turns out that birds are not sensitive to the effects of capsaicin. Thus, capsaicin repels animals whose chewing action may destroy the seed while not repelling birds. Additionally, capsaicin may function as a antifungal.

What does capsaicin do, chemically?

Capsaicin binds to receptors for heat and pain called vanilloid receptors. Capsaicin causes the receptor’s neuron to fire, which normally occurs at higher temperatures; thus, the brain interprets this neuron signal as sensing heat.

Capsaicin is just one kind of vanilloid compound; vanilla is another member of the vanilloid family, with a similar structure, but it does not act on vanilloid receptors. Now I wonder if peppers taste at all like vanilla to birds. A mystery for the ages.

Capsaicin in peppers

As you may have noticed, some peppers are hotter than others. This is because some contain more capsaicin and related chemicals than others. The relative hotness of peppers is measured by the Scoville scale. According to this scale, habañeros are a few times hotter than ají peppers which are a few times hotter than chipotle peppers. Bell peppers actually don’t contain capsaicin due to a recessive trait.

Contrary to what I learned growing up, the seeds don’t contain capsaicin. However, the pith that surrounds the seeds has the highest concentration. This may be why the hottest peppers look like wrinkly sphinx cats; they are just packed with pith (such as the Carolina Reaper pepper, bottom). You can reduce the hotness of a pepper for cooking by preferentially removing the white spines, which is the pith.

Habañero peppers have a Scoville rating of roughly 500,000. Pure capsaicin has a rating of 16 million. Some chemical called resiniferatoxin found in Moroccan cacti has a rating of 16 billion (1,000 times higher!). 40 grams of the stuff can kill a person.

So, there’s your overview of peppers for this Friday. Don’t consider this a challenge to go find that Moroccan cactus, but when your lips tingle after eating salsa, perhaps think of capsaicin.

Carolina reaper peppers, one of the hottest according to the Scoville Scale. Just look at the wrinkles! (Wikipedia)

Food and Science: Caramelization and the Maillard Reaction

When we cook food, we want it to be as flavorful as possible. Two types of chemical reactions contribute to browning; both of these reactions create hundreds or thousands of other molecules, which then add aroma and flavor. The higher temperature reaction you may be familiar with: caramelization is the breakdown and reaction of sugars. The Maillard reaction occurs at slightly lower temperatures (still usually above the boiling point of water); this reaction occurs between the amino acids of proteins and sugars.

Both of these reactions are so complex that scientists don’t know everything that occurs during them. We understand the basic nature of each reaction, but any plant or animal food contains literally thousands of different molecules that can all react together. Fortunately, we can still implement the process without a full understanding (and we have been for millennia), and a lot of very nice foods undergo either or both reactions.

The Maillard reaction and caramelization often occur at the same time, and produce similar results visually, so they can be tough to separate. If something contains both proteins and sugars, both reactions can occur with heat. Fortunately, they both taste good. They’re also easy to do at home. If you want to brown your food, get a skillet nice and hot. Make sure you’ve patted the food dry (this allows the surface to get hotter than the boiling point of water, thus allowing the reactions to occur), and sear away.

Food and science: sous vide or water bath cooking

In sous vide cooking, food is cooked in a water-bath at low temperatures (130-150 F) for longer times. Food cooked sous vide can be radically different in texture and taste than food cooked by more traditional methods. Even better, sous vide cooking is really, really easy.

What is sous vide?

In sous vide cooking, food in plastic bags is placed in a fixed-temperature water bath. The water bath temperature is held most easily by a digital controller. Some people build their own systems on the cheap. I bought this one, which in my opinion is worth every bit of $200.

As I discussed last week, bacteria die above 125 F. Consequently, food can be cooked at any temperature above 125 F (the closer to 125 F, the longer required for sanitation). This means a steak can be cooked to 130 F and be rare throughout, but also safe. For a 1 inch thick steak, this takes about an hour.

Why is it different?

Like a crock pot, sous vide cooking can be used to make tough cuts of meat extremely tender. Unlike a crock pot, the user has precise control over the set temperature, and the food is isolated from the water in which it cooks. This means that sous vide food isn’t soggy like slow cooker food so often is.

When we cook meat, the textural and color changes we observe are due to changes in the protein of the meat. Different proteins break down at different temperatures. The controller I use (linked above) allows control down to 0.1 C or 0.5 F. With such fine control, the cook can choose the exact temperature at which they wish to cook, and thus the effect they’d like to have on the protein. Poached eggs best demonstrate the results of this control. The proteins in the yolk coagulate at lower temperatures than the proteins in the white. By changing the cooking temperature only slightly, the cook can dramatically change the textures in the poached egg. This is called the perfect egg–at the link you can see eggs cooked to a variety of temperatures.

The set-up

For my set-up, the only major cost was the controller. I clamp it to the edge of a 8 qt pot (bigger would be better, but it’s what I had). Many people vacuum-seal their food before cooking, but the sealing system is an additional cost. I put my food in ziplock bags (glad bags are reported to be BPA-free). Then I add a little oil, squeeze the air out, and seal. To start cooking, I wait for the water in the pot to heat up and I clip the bag to the edge of the pot with a clothes pin.

Recipes and further reading

  • Citizen sous vide: an excellent general guide, with links to recipes and product reviews. Recipes are sorted by meat and cut.
  • Douglas Baldwin’s A Practical Guide to Sous Vide: a more technical discussion of sous vide with straightforward and instructive videos. This guide really explains the motivations of cooking sous vide.
  • Recipe for tri-tip steak: this recipe suggests cooking a tri-tip at 130 F for 6 hours, results shown below. You can see the meat is still pink in the middle. Cooking for six hours allowed it to tenderize, and all I had to do was cut up some meat and stick it in a bag. Very easy and delicious.
  • Tri-tip steak cooked sous vide.

    Tri-tip steak cooked sous vide.

Food and science: when is food safe?

The milk we get at the store is pasteurized, and we all know that chicken must reach 165 F and pork must reach 145 F. What is the source of these numbers, and what is their purpose?

Raw foods like meat and dairy contain a certain number of pathogens that can make us sick. These pathogens die when heated above about 125 F. So why are cooking temperatures much higher than 125 F? The recommended cooking temperatures are the temperatures your food must reach in order for a large enough portion of the bacteria to die nearly instantaneously. At 140 F, the salmonella in ground beef is reduced by a factor of ten every 5.48 minutes. Salmonella must be reduced by a factor of ten million to one, so you would have to hold this temperature for a while. At 150 F, the salmonella is reduced by a factor of ten every 0.55 minutes, so this is quite a bit faster. At 160 F, the bacteria reduces fast enough that by the time you’ve measured it, enough time has passed. The process of “sous vide” cooking uses lower temperatures applied steadily for long times to cook food. I will discuss this excellent cooking method in a future post.

The process of making food safe by reducing the bacteria is called pasteurization, which you may be more familiar with from the dairy aisle than meat, but the concept is the same. Also in dairy, the time for pasteurization depends upon the temperature. Pasteurized milk is heated to 162 F for at least 15 seconds while ultra-pasteurized milk is heated to 280 F for 1-2 seconds. Eggs are not usually pasteurized, but they can be when heated to 130 F for about an hour.

Douglas Baldwin’s section on food safety in his online guide to sous vide is the source of much of the information I present here. It is full of scientific citations, but is very readable, and I highly recommend it as further reading. Happy Valentine’s Day!

Why I cook: food and science series

I cook a lot. I cook because it’s cheaper, but mostly I cook because I am absurdly lactose-intolerant, with a generally fussy tummy. As a kid, cooking seemed like something girly and irrelevant; food simply appeared. Now I see that eating is something we do every day and it can be either drudgery or exquisite.

This post is the first of a series I will post each Friday. Other posts will talk about specifics: science, recipes, and methods. Today I will talk more about how cooking became something I spend time on, and why cooking matters.

In college, I picked up some kind of food poisoning, probably on dorm food. I started to get sick a lot. I lost weight. I drank bulk-up drinks like body builders do. I became sensitive to milk products; I switched to lactose-free milk, and started drinking whole milk. I couldn’t move after meals, or else I’d get sick. If I ate even a bite too much, I got sick. If I got too hungry, I got sick. My lunches were often half a pizza slice. I bottomed out with a BMI below 18. Doctors seemed disinterested my inability to keep food, but they couldn’t explain the weight loss.

Finally, I started taking probiotics, which seemed to help. Now, seven years after my minimum weight, I’m at my high school weight, with gain more of a concern than loss. I cook most meals for myself, where I have control over my intake. Eating out with others isn’t easy, because I must be picky and inflexible about where and when I eat. I can’t wing it. If I deviate from the rules too much, I will get sick, which directly affects me for up to a day, and destabilizes me for the future. It’s manageable; some people with IBS get sick a dozen times a day, and digestive illnesses like Crohn’s disease can be life threatening.

The gut is understood very poorly, despite its importance. The enteric nervous system, or gut brain, is the site of 90% of serotonin and 50% of dopamine. With my ups and downs, I know well the relationship between gut health and mood. The digestive system is second in neurons only to the brain, and contains more neurons than the spinal cord. It is the engine of our body, and it functions in tandem with more bacteria than there are stars in the galaxy. Yet Americans spend the least time cooking of any country on Earth.

Loads of scientific evidence and my own personal evidence shows that a happy tummy goes a long ways towards a happy person, even in cases less extreme than mine. Good food can be a blissful experience, and in these posts I’ll talk about some methods toward good food. I don’t believe in diets or supplements or shortcuts, just making food that works. Good food can be made in a small kitchen on a limited budget with limited time. The primary ingredient is our own interest and curiosity, which I intend to share here.

Science and Cooking

I love to cook. As one might gather from this blog, I like to keep my hands busy, and cooking saves money and provides deliciousness. (Many other hobbies have more of a knack for consuming money.) I also happen to be very lactose-intolerant, so cooking for myself also greatly benefits my digestive health.

When I was younger, I was absolutely apathetic to cooking, as I suspect many kids are, feeling that it’s house-wifely and unimportant. Then I got out on my own, and, astonishingly, good food was expensive and I had little currency.  I wanted to improve my cooking, but I really didn’t know the rules. But I knew the next best thing: science. Many recently published books explore the relationship between science and cooking. For those of us that can’t remember the baking soda without knowing its chemical purpose, this is a great thing.

Some recommended books:

  • What Einstein Told his Cook by Robert Wolke. The content is good, especially for those less versed in chemistry. The author wrote a newspaper column about cooking, and this book is mostly the compilation of answers to various questions such as “What is the difference between cane sugar and beet sugar?” It contains several recipes illustrating various points of the book. A major emphasis of the book is clarifying common misunderstandings of food science. As someone who knows a lot of science, I sometimes find the answers too basic, but I definitely learned things reading this book.
  • Molecular Gastronomy: Exploring the Science of Flavor by Herve This. Of the three books I discuss, this is the one I have had the least time to scrutinize. However, I really like what I have read. Wolke’s book covers more conceptual topics, like the differences between various kinds of salts. This’s book covers more specific topics, like why we marinade roasts in red wine rather than white, or how different kinds of truffles are related. This one is probably most strictly for those interested in cooking, with fewer “gee whiz” moments and more “that would be useful” moments.
  • Cooking for Geeks: Real science, great hacks, and good food by Jeff Potter. This one is definitely the most fun of the three! This book is from the publisher O’Reilly, which does a lot of technical textbooks. This book shares its layout with those kinds of book, but its soul is lighter. Its layout is more varied, as textbooks are. Plus, this book has a fun section about hardware like evaporators and sous vide water baths. Sous vide is involves cooking foods in circulating water baths. It is similar to slow-cooking, but the food is kept in a plastic bag and thus not diluted. Foods can safely and extra-deliciously be cooked at much lower temperatures by this method. Low temperatures denature specific proteins, prevent drying, and, when held for a bit, kill bacteria. This book does a great job explaining why and how sous vide works. I just got a sous vide system myself, and this book has given me some confidence about something I knew very little about. Plus it’s very fun to read, and covers tons of other topics in geek-friendly ways.