A few weeks ago I finally had enough of the cold brew trend and decided to see what all the hype was about. I followed this recipe (because $5 at Starbucks is just too much for me), and was surprised to find cold brew wonderfully smooth, sweet and mild. I love coffee, and though I drink it with milk and sugar, I’ve never especially been bothered by the bitterness or acidity of traditionally brewed coffee. None the less, cold brew is quite amazing, and it left me wondering what the chemistry behind it was.
It turns out that hot water (about 93 ℃ in most drip coffee makers ) accelerates the extraction of molecules and chemicals that, once mixed with water, form the coffee we know and love. Once brewed, the coffee continues to react with air and water molecules. This is why coffee goes stale. Heat accelerates these reactions (as it does most), so coffee left on a burner, or in your car, all day goes staler more rapidly.
In cold brew, however, there is no heat to help extract these molecules and to cause the break down of others. The time the cold brew is left brewing allows the chemicals to be extracted from the coffee grounds much like the heat does, but you do get different amounts of different chemicals, leading to a different taste. Notably, many molecules that taste bitter are not extracted in large amounts in the absence of heat, which explains cold brew’s sweetness. You may have also seen cold brew being sold pre-packaged in stores, a possibility that is afforded to it due to the cold water not accelerating the ‘staling’ process.
So for once it seems like the hype was justified, though I’ll stick to making my cold brew at home.
Its catapult to popularity may have been triggered by the pandemic-induced yeast shortages, but even months later, when instant yeast is once again available at most grocery stores, sourdough’s contemporary stardom is barely starting to fade. Sure, many of us turned to making a sourdough starter to simultaneously combat yeast scarcity and our newfound fear of going to the grocery store. But lots of us have kept up with our strange new hobby of mixing water with flour and leaving it on the counter for reasons beyond just the practical.
If, like me, you aim to cook dinners that provide both your next day’s lunch as well as a freezer portion to be thawed at some future date, you may want to stop. At least with rice.
Uncooked rice can contain spores of Bacillus cereus, a bacterium that can cause two different types of food poisoning. The first type is characterized by vomiting (and thus is called the emetic form). It results from consuming a toxin produced by the bacteria while they’re growing in your food and has a short incubation time of 1-5 hours. The second is characterized by diarrhea (and is non-surprisingly called the diarrhoeal form). It results from a toxin that is produced in your small intestine as the bacteria grow there and has a longer incubation time of 6-15 hours.
The two forms are commonly associated with different types of foods. The diarrhoeal form has been linked with foodstuff like soups, meat, vegetablesand milk products including formula. The emetic form comes from a more limited list of culprits, as it’s mostly associated with starchy foods that have been improperly stored like rice, pasta, pastries or sauces.
But what does “improperly stored” actually mean?
If a raw food is contaminated with B. cereus (as much rice is) and then cooked, some spores will remain in the cooked product (unless you’re in the habit of heating your rice to above 100 ˚C for extended periods of time). These spores, If left standing in temperatures between 10 ˚C and 50 ˚C, such as on your stove or countertop, find themselves in their ideal environment (wet and warm) to germinate, grow and produce the toxin that will make you sick.
It doesn’t take long for the spores to reproduce either. A colony of B. cereuscan double in size within 20 minutes if kept at 30˚C. The routine reheating of your food will not help to deactivate the toxin or kill the bacteria. Since this bacteria and its toxin are so resistant to heat your only hope of dodging food poisoning is to avoid allowing the bacteria to germinate.
To sidestep a nasty bout of illness caused by B. cereus you should aim to eat your food as soon as possible after it is cooked. If you can’t do that, then hot foods should be kept above 60˚C and cold foods, below 5˚C. Meats and vegetables should be cooked to an internal temperature of 60˚C and kept there for at least 15 seconds. Frozen foods should ideally be thawed in the fridge or as a part of the cooking process.
If storing leftovers for later, they should be rapidly cooled in the fridge as fast as possible (according to the NHS, within 1 hour is best). You should avoid storing hot leftovers in deep dishes or stacking containers together, as it will cause the food to cool slower. When reheating leftovers make sure they reach an internal temperature of at least 74˚C and don’t keep them for more than seven days, even in the fridge.
When dealing with high-risk ingredients (like rice, grains and other starchy foods) it’s best to not keep leftovers at all. But if you do, try not to keep them for more than one day, and never reheat them more than once. Even freezingdoesn’t kill bacteria but rather just stops them from multiplying, so, by all means, freeze your leftover curry, but make fresh rice when it’s time to eat it again.
Considering the amount of improperly stored rice I now know I’ve eaten it seems almost a miracle that I haven’t gotten sick yet. Then again, food poisoning with B. cereus is often confused with the 24-hour flu, so I may have already paid for my mistakes without even knowing it.
Let’s all learn from my mistakes and start storing our leftovers properly.
Students from the Edge Hotel School have brought us some starchy math that can improve the quality of roasted potatoes the world over.
The theory is that maximizing the internal surface area of the tuber will maximize the crispiness and therefore the desirability of roasted potatoes. Most of us cut our potatoes at 90˚ angles, in half, and then into quarters. These students realized that just by cutting at 30˚ angles, an increase of up to 65% internal surface area can be achieved!
You can view their method in the images below. Their calculations are based on a 5 cm by 11.5 cm potato, so the specific numbers will differ depending on the spud, but since most potatoes are spheroids the principle will hold true.
Science can also help us out with how to improve the pizzas we bake at home.
A traditional Italian pizza oven features curved stone walls, a stone floor and a wood fire burning in one corner. These ensure that heat radiates uniformly throughout the oven. When the heat of a pizza oven is 615 – 625 ˚F a traditional thin crust margarita pizza will be completely cooked in 120 seconds. The heat can be increased to 730 ˚F, in which case the pizza will be cooked in only 50 seconds, but the quality will be poorer. Pizza restaurants will often do this during rush hours in order to keep up with demand, leading pizza aficionados to recommend only getting pies before 8 or after 10 pm.
These temperatures and times only hold true for a wood-fired oven. When cooking pizzas at home, most of us will place them on a metal tray or oven rack. Metal, however, has a different heat conductivity than stone, so that tray or rack will heat up much faster than the stone floor, and your pizza winds up overcooked.
This can be remedied by decreasing the temperature. Knowing by how much was the hard part, but luckily the researchers have solved the complex thermodynamic equation for us. In the end, the authors recommend cooking your thin crust pizza in a convection oven for 170 seconds at 450 ˚F (although any toppings added will increase the time needed to cook the pie).
Trying these methods, you may just wind up with a better dinner, all thanks to science.
Ghee can be found in the international section of most grocery stores, and clarified butter on the pages of many culinary magazines, but what are these fats, and how do they differ from normal sticks of butter?
Butter is made from milk, which itself is composed of globules of butterfat suspended in water, with carbohydrates, minerals and proteins dissolved in the mix. So, when you melt butter it separates into three layers.
From top to bottom they are milk solids (the proteins, minerals and carbs), butterfat, and a combination of more milk solids and water. Clarified butter is simply this middle layer of butterfat, which can be attained by skimming milk solids off the top, evaporating the water, and decanting the butterfat.
Ghee simply requires an extra step: simmering. After the risen milk solids are skimmed off the top, the butterfat, with sunk milk solid still present, is simmered until it begins to brown. The browning of the milk solids provides the nutty flavour that makes ghee so desirable. The butterfat is then decanted off, leaving the browned milk solids, but taking some of their flavours with it.
Why go through this skimming and decanting hassle? A few reasons. First of all, because you’ve eliminated almost all of the milk solids, clarified butter and ghee are essentially lactose-free, something your lactose intolerant friends will appreciate considerably.
Second, butterfat, unlike the butter is was made from, does not burn at such low temperatures. Where butter’s smoke point (the temperature at which an oil begins to create a smoke, and its associated bad flavour) is 302˚F (150˚C), clarified butter’s smoke point is 482˚F (250˚C), which allows it to be used to cook at higher temperatures than any other standard cooking oil.
Thirdly, ghee and clarified butter are shelf stable. They can last about 12 months once opened, or many years if not opened, making them an attractive option for emergency kits, campers or those in rural areas.
If you’re not cooking at really high temperatures, lactose intolerant, or an adventurer, however, there’s no reason to switch to the clarified variety of your toast spread.
While ghee has been part of traditional Indian medicine (specifically ghee made from breast milk) there’s no evidence to support the many health claims made of this fat. Ghee and clarified butter are almost nutritionally identical to the butter from which they’re made.
In the end, clarified butter is still butter, and butter is not a health food.
Our good friend the Food Babe has published an interesting piece of pseudoscience writing entitled ‘Are Natural Flavors Really That Bad? (MUST WATCH)’. If you’re looking for the quick answer to this superfluous, click-bait title, let me tell you that it’s no: natural flavours are perfectly safe and healthy. But if you’re looking for an explanation of how taste actually works (and why her claims about natural flavours are utter nonsense), then please read on!
Vani Hari bases her distaste for natural flavours off the idea that “flavor in nature doesn’t come without nutrition.” Regrettably I’m here to tell her that this is unequivocally false. Hari thinks that “foods naturally taste amazing to us because they contain the nutrients we need. Flavors are the cue that tells us where to and the nutrients we need”. Not quite, Babe. Taste =/= nutrition. There are poisonous things that taste great, and very healthy foods that taste awful.
Following this same logic, she also believes that food companies add natural flavour to foods to “trick consumers into thinking they are getting nutrition that isn’t there.” Now, for once, this idea isn’t exactly wrong, but it is misleading. Food producers definitely do add natural flavours to all kinds of foods, but they do so in general to make things taste better, not to make them seem healthier. Think about it, do you really think your soda is healthier if its blueberry flavoured instead of cream soda? Doritos list natural flavours on their label, presumably those are natural flavours of tomato and cheese, but did you really think that Doritos are good for you like homemade tomato soup with cheddar on top?
Following your tongue to guide your diet probably isn’t a good idea, but I think we all knew that. If I only ate what I was craving, I’d live off of French fries, and I don’t think that’s because my body needs a lot of sodium and no protein. Besides, what tastes good is fairly subjective, but what’s healthy isn’t.
So what is flavour, if not nutrition? It’s all chemistry. We taste things because of interactions between the chemicals (gasp!) in food and the chemoreceptors in our mouths. You know how they say there are only 5 tastes: sweet, sour, salty, bitter and umami (savoury)? That’s a result of the taste receptorspresent in humans.
Salty and sour tastes are the simplest in many respects. Saltiness is detected by sodium ion channels in our tongues. When sodium ions (usually from sodium chloride or table salt) interact with these taste receptors, they are allowed to enter the cell. Being positively charged, they change the voltage inside the cell, which starts the process of sending an electrical signal to your brain that tells it, ‘hey, this tastes salty’. Sour tastes use a similar process, but with hydrogen ions entering sour taste cells.
The other 3 tastes are a bit more complex in how they’re detected. Instead of ions entering receptors directly and starting the signal to the brain, various molecules (depending on the taste) interact with different G-protein-coupled receptors. This interaction begins a whole pathway of signaling that eventually reaches the brain to convey taste. Many different molecules may activate these: for sweet tastes, it’s commonly sugars and molecules similar to sugars; for bitter, it’s more than 670 compounds; and for umami, it’s salts ofglutamic acid, the most commonly encountered of which is monosodium glutamate (MSG).
So food produces a taste because of the molecules inside of it, but why does it taste good? Because of physiology!
Our body does use the tastes of foods to get us to eat varying amounts of them, but not because of their nutrient contents like Hari thinks. In general, we find salt to be a pleasant taste because it is necessary to maintain homeostasis. Without salt, our kidneys would cease to function, so in an attempt to get us to ingest it, our brain makes it taste ‘good’.
Sugar, similarly, is absolutely integral to life. Carbohydrates are just chains of sugars and they are rich in calories, so they are desirable for a body that needs energy, hence the enjoyment that sweet tastes elicit. Umami tastes ‘good’ to encourage us to eat necessary fats and proteins.
Both salty and sour tastes are only ‘good’ in certain quantities. This is thought to be a result of evolution, since things that taste too acidic or salty tend to be spoiled, unsafely acidic or not ripe.
Bitter tastes bad to all humans naturally: just try to feed dark chocolate to a baby if you need proof of that, and it’s only through repeated consumption and some trick psychology that we come to enjoy bitter things. This is anevolutionary development due to many poisonous compounds tasting bitter, and why most medicines still taste bitter to us (our bodies think they’re poisons).
Now, there are many exceptions to these broad generalizations of what tastes ‘good’, proven in the fact that some (silly) people dislike dark chocolate, or the fact that I hate papaya, despite it tasting sweet. And in the modern world, as Food Babe warns us, there are artificial and natural flavours added to foods, so, surprise, surprise, there’s more to a healthy diet than just flavour.
Some good example include nightshade, which is incredibly toxic to humans, yet tastes quite sweet (making it even more dangerous to children who may ingest it), and apricot kernels which are quite toxic (as few as 10 of them could kill a child) due to their amygdalin content (this compound is metabolized into cyanide inside humans). But if you want to follow Vani’s logic, some people think they taste quite good, so they must be good for you, right?
Vani might be technically right about natural flavours being added to foods, but she’s wrong about why, and she’s wrong about a few other things too:
She says that “the flavors that humans love in tomatoes are synthesized in tomatoes from essential nutrients like beta carotene, amino acids, and omega 3’s”. Well, beta carotene is not an essential nutrient in humans, and indeedonly 9 of the 20 amino acids are. Studies on tomatoes have determined that there are about 27 compounds that contribute to their taste, 3 of which (geranial, 2-methylbutanal, and 3-methyl-1-butanol) actually influence how sweet a tomato tastes, regardless of sugar content (or ‘trick your brain!’ as she would say). So if the Food Babe believes compounds that alter how foods taste without altering their nutritional content are problematic, she should probably give up bruschetta.
Not to mention she claims that “soda without flavors is just carbonated water and sugar. No one would drink that without the flavor”’ somehow forgetting that the carbonated water industry is huge, and that billions of people do just that.
To recap, flavours are just the result of chemistry, things that are good for us do taste good, sort of, but not because of their nutrient content, and no one thinks that gummy bears are healthy just because they taste kind of like fruit.
So instead of asking yourself, “Did someone engineer this to be delicious or did nature engineer this to be delicious”, as Hari advises, I think I’d rather contemplate why it is I’d be taking diet advice from a blogger without a science degree.