Tag: Fascinating Fridays

The Science of Sourdough: Fermentation, Wild Yeast, and Flavor Development

July 7th, 2023

At the beginning of the pandemic, just over three years ago, Google Analytics showed a huge increase in the amount of traffic generated from baking and cooking at home. You can see in the graph below that sourdough reached its peak popularity on Google searches just as the pandemic was gripping the nation. It makes a lot of sense too; people were desperate to find things that they could complete entirely in their homes, especially those that could reduce the number of items that were on a grocery shopping run and potential exposure to this new virus floating around. Now, sourdough recipes are appearing all over the internet, with burgeoning food blogs displaying their new bakes’ beautiful designs and perfect pairings. But what is happening behind this explosion of sourdough in the kitchens of the home baker? We’ll delve into the science of what gives sourdough that distinct flavor and some tips on how you can get started at home yourself.

Starting Starters

Sourdough contains a very simple set of ingredients: flour, water, and salt. That’s it! For a loaf that tastes seemingly so complex, the process requires a very small amount of input factors. However, sourdough’s leavening factor makes it unique. Rather than using a typical commercial yeast that you can buy from any grocery store, sourdough utilizes a fermented culture of flour and water, also known as a starter. This starter begins with equal parts flour and water by weight (it’s recommended that you use unbleached flour, such as the King Arthur brand to avoid any possible issues with starter forming) that comes in contact with natural yeast.

***Natural yeast, also known as wild yeast, are natural multi-micro flora that becomes seeded in a dough that has been left exposed. These are the basis of starters and bread across the world, as the yeast that generates in a starter dough is typically the same worldwide. Most yeast in these starters is a strain of the species Saccharomyces cerevisiae, with some other yeasts and lactic acid bacteria. These varieties of organisms that exist with S. cerevisiae are typically what give the sourdough its flavor. Lactic acid bacteria give sourdough a yogurt like flavor, while acetic acid-producing bacteria give it more vinegary notes**

Natural yeast are single-cell organisms that are incredibly useful in baking and fermenting projects, as they break down the sugar and starches in dough and convert them into carbon dioxide and ethanol. They are also what give beer its bubbles and alcoholic content. The yeast converts the sugar into carbon dioxide and ethanol through a process called anaerobic respiration, which means that it does not need oxygen in order to complete the reaction. Glucose, or the sugars present in the flour, are broken down by glycolysis (literally meaning “sugar decomposition”) which produces 2 carbon dioxide molecules, 2 alcohol (ethanol) molecules, and 2 energy molecules. The process is written below in scientific notation:

C₆H₁₂O₆→ 2CO₂ + 2C₂H₆O + 2ATP

This is why when we watch our starters grow and form over the first couple of days, we begin to see bubbles form and pop throughout the mixture. Carbon dioxide is formed via the yeast’s breakdown of the sugars and starches. The starter can also begin to form the ethanol that comes from the reaction in large enough amounts to be seen. This is called “hooch” and means that your starter needs to be fed again. While it wouldn’t be the worst thing to ingest the hooch that is coming from your starter, it is recommended that you pour off any hooch that has formed before feeding your starter again. But that is getting ahead of ourselves.

For an easy starter, mix sixty grams of unbleached flour and sixty grams of warm water, about one-half cup and one-quarter cup, respectively. Mix the two ingredients until it becomes smooth and thick. Cover the mixture in plastic wrap or a lid if mixing in a jar and let sit in a warm spot for around 24 hours. After this time, this is when we are inspecting for the bubbles mentioned earlier: we want to make sure that our starter has begun to ferment, which is indicative of yeast having come in contact with our mixture. Rest the mixture for another twenty-four hours, and don’t worry if there are not any apparent bubbles. Sometimes starters need a bit more time, especially depending on the type of flour you used to start. After day two, this is when we typically see the presence of hooch. Again, this means that our starter is “hungry” and needs to be fed again. Remove around half of the mixture in the vessel you are using and replace it with a “feeding” of sixty grams of flour and sixty grams of water. It will begin to rise and create more bubbles throughout the culture, and once its falls, it is time to feed the starter again. Usually, after a week from beginning the process, the starter will be doubled in size and its texture will be spongy and soft. It also should begin to smell a bit like yeasty bread. If it smells like alcohol (or some describe it as stinky feet), it means that your starter is underfed and needs some new flour. If all is well, your starter can be transferred to a new clean dish and you are ready to bake!

***NOTE: Some starters can be ready in a week, while others can take up to ten to fourteen days to complete. Once you have seen the activity begin to diminish and the texture is described as above, your starter is ready to use***

Anatomy of Bread

Sourdough and other breads all have the same anatomical structure: crust and crumb. The crust is formed as the starches in the dough begin to absorb moisture from within the bread and the oven atmosphere. As they gain more moisture, they eventually reach a breaking point, liquifying the starch and becoming a gel on the outside layer of the bread. A higher moisture content on the bread surfaces directly correlates to a crisper crust, as there is now a larger quantity of this starch gel on the bread. The caramel color of the crust comes from the Maillard Reaction, which was talked about more in-depth in an earlier post. The rigidity of the crust also comes from the coagulation of gluten molecules (which before was what gave bread its elasticity).

The crumb is the interior of the bread or anything that is not the crust. The water and flour that are used throughout the baking process are the greatest determiners of the final crumb structure. In the initial mixing, gliadin and glutenin (proteins available in the flour) combine to create the gluten that helps trap gases during the baking process. The more available gluten means a higher likelihood of entrapped carbon dioxide within the viscoelastic structure of the bread. The particular carbohydrate fermentation that occurs to provide this carbon dioxide is called the tricarboxylic acid cycle. The equation for fermentation is the same as the one listed above. Fine texture crumb is described as thinner walls between the open cells of the bread, while coarse is for larger cell walls. Breads that have higher water contents or lower salt contents are likely to experience very large cells, like a Swiss cheese slice.

Flavor Development

Flavor development of a sourdough loaf occurs at all stages of the baking process. The types of flour, whether rye, whole wheat, barley, or more, can impart the particular flavors that accompany those whole grains. Buckwheat flour makes a vinegary starter, whereas amaranth flour is toasty, and sorghum is a more fermented, yeasty smell. You can also have a drastic change in the sourdough flavor based on the bacteria that become entrapped in the dough during the initial starter phase. Starters with lower water contents, also known as “stiffer starters,” can encourage the lactic acid bacteria to create a sharp acetic acid taste, similar to vinegar. Higher water content, or runnier, starter? The lactic acid bacteria give a smoother, creamier tang to the bread compared to the sharp acetic acid. Fermentation of the starter in a warmer kitchen makes lactic acid bacteria create a sourer dough, but cooler temperatures (like storing your starter in the fridge) allow the yeast to produce a fruitier flavor.

Sourdough has been around for thousands of years, as the natural impregnation of yeast in sitting doughs has been taken advantage of since the times of the ancient Egyptians. With the more recent boom during the beginning stages of the pandemic, it has shown that we don’t need to always be buying a jar of yeast from the store in order to make delicious, fresh bread in our kitchens. Sometimes, with just a little flour, water, and salt, we can make science into tasty and beautiful creations.
Fascinating Fridays: Bromelain

June 30th, 2023

One of my favorite fruits when perusing through the produce aisles is pineapple. Its funky almost pinecone-like shape and its sharp, rigid leaves belie the delectably sweet yet acidic golden pulp. After finally getting it home, the smell that wafts up from the cutting board elicits images of tropical salsa on chips and refreshing pina coladas while sitting on a warm beach. With my mouth watering watching freshly cut pieces falling from my knife, it takes almost all my willpower to make it to the end of prep to put a piece in my mouth. The wait has never been fruitless; that first piece that I get into my mouth burst with that far-away loved flavor, the juicy pieces instantly putting a smile on my face as I grab another and another. Soon though, I can feel my mouth getting sore, almost like I’ve been eating something incredibly hot or a very sour candy. The more pineapple pieces that I eat, the more intense this feeling becomes. What is causing this? How can something that smells and taste so sweet create a raw feeling like this in my mouth? The answer lies in an enzyme that is found in the pineapple, both in stem and the fruit: bromelain.

Bromelain is a group of active enzymes that is found in the pineapple plant’s fruit and stem. These enzymes assist in the breakdown of the proteins at their amino acid bonds. Depending on the protease that the enzyme may have, it breaks down the proteins at different parts of the amino acid chain. Serine (or the RNA structure AGU/UCG), cysteine (UGU/UGC), or threonine (ACU/ACC) are examples of some of the amino acids that are in a protein chain. Bromelain is a cysteine protease in particular, so wherever the amino acid chain contains a cysteine structure, bromelain will come in and conduct a proteolytical process.

A metric that should be noted of the bromelain that is in the fruit versus the bromelain in the stem is that fruit bromelain contains 90% of the “proteolytically active” material in the pineapple, meaning that the fruit of the pineapple contains 90% of the enzyme that feels like it is slowly dissolving your mouth (or tenderizing the proteins you may place in it). A protease, from proteolytic, is a “cleaver” of peptide bonds, which is also known as a process called hydrolysis. Hydrolysis is the breakdown of a water molecule into two parts, a positive H+ ion and a negative OH- group. In this particular reaction, the breakdown of the proteins is called proteolysis. In our bodies, we undergo proteolysis when we eat various protein sources, where we break down our foods into the amino acids that create them and then rebuild those amino acids into protein structures within our bodies. In the case of bromelain, it is accelerating in the breakdown of the protein in its vicinity, our mouths. This is why we begin to feel sore after eating a couple cups of pineapple. The bromelain is breaking the proteins or peptide bonds into the amino acids that, if coming from the foods that we are eating, we can create new proteins for the body to use.

***You may think this would exist in every iteration of pineapple in various dishes, but proteins have a tendency to denature (or breakdown) under heat. Most enzymes denature at around 55 degrees Celsius, or 130 degrees Fahrenheit. Bromelain denatures at 158 degrees Fahrenheit, which is slightly below the recommended consumer cooking temperature for eggs, rabbit, or red meat cooked at medium (160F). This explains why cooked pineapple is sweet without so much of the bite that comes from the freshly cut pieces***

Bromelain is a enzyme that is not at the fore front of everyone’s mind, but does play a crucial role in a meat/protein tenderizer for many recipes. When you look at a meat tenderizer like McCormick in the grocery store, bromelain is the hidden wonder in that powder boosting the tenderizing power. So, whenever you are enjoying the slice of pineapple on your pina colada and feel like small bite back, hopefully you give bromelain a brief bit of appreciation during your vacation.
Fascinating Fridays: Caffeine

June 2nd, 2023

Caffeine. One of the few substances on Earth that I am sure most people say they could not do without. Whether it is coffee, energy drinks, teas or just munching on a handful of chocolate-covered espresso beans, it is being taken in by roughly 90% of the world’s population on a daily basis. This beats out the 29% that drink alcohol or the 25% of the world population that uses nicotine. It also makes coffee the most consumed psychoactive drug (and the most socially acceptable one). In this Fascinating Friday, we delve into the way that our body takes in caffeine and its physical and psychological effects.

Caffeine is classified as a stimulant, meaning that it increases the activity of the central nervous system and the body in general. Specifically, it falls in the methylxanthine class of stimulants, which is joined by similar substances, such as theobromine (interestingly both found in chocolate and synthesized by the human body after ingesting caffeine) and theophylline (which is found in teas like yerba mate and the kola nut). In its pure form, it is a bitter, white crystalline powder. It is closely related in structure to adenine and guanine, which are two of the base nucleotides in our DNA and RNA. In the brain, there is a large nucleotide molecule called adenosine, which uses adenine as a base when is attached to a sugar molecule, ribose. You may have heard of adenosine in your school biology classes, where it was commonly represented in the compound adenosine triphosphate or ATP, the energy storage molecule of the body. Because caffeine is similar to this prevalent molecule in our bodies, it has an increased ability to bind to the same receptors in the brain. This means that it inherently blocks the ability of adenosine to bind to their receptors, but also increases the base nerve activity. This is what gives you those coffee jitters, leaving you feeling more awake and energetic.

The effects after intaking caffeine happen quickly, potentially due to the similarities of its chemical makeup and our base DNA nucleotides, and the effects on the human body can be felt within an hour of taking the substance. It is fairly soluble in its pure form, with water at body temperature being able to absorb around 20g/L before being too saturated to absorb more. However, with an increase in water temperature (at most to just below boiling) and the presence of an acid (which coffee beans provide), the solubility increases greatly. By the time you are taking your first sip of a freshly brewed cup of coffee, the new concentration of caffeine can be up to 660 g/L. In comparison, salt placed in nearly boiling water can only take in 359g/L before dropping out of the solution. Caffeine affects the CYP1A2 enzyme, which is a primary enzyme in the detoxification of the body, found primarily in the liver. This can result in a change in the efficacy of certain medications, as routine caffeine intake can result in up to a 20% decrease in the CYP1A2 enzyme efficacy.

***For a real-world example, coffee is shown to reduce the efficacy of escitalopram oxalate (more commonly known as Lexapro) by 28% in human trials. It also affects the intake of necessary vitamins and minerals. Iron absorption after caffeine intake can be decreased from 39%-90% after a single cup of coffee. Conversely, some medications have higher concentrations in the body after caffeine intake: taking a 650mg tab of aspirin with caffeine (120mg, or a cup of coffee) shows a peak of ~60 micrograms per milliliter vs. a peak of ~45 micrograms per milliliter, an 33% increase.***

The physical effects of caffeine show that it can increase performance in aerobic sports, especially those that require prolonged endurance. These athletes show delayed symptoms of muscle and central nervous system fatigue, meaning that they can operate for longer at that increased effort level before needing to take a break. For individuals that are considered to have lower physical fitness, it is shown to have an increased effect on the oxidation of fatty acids, meaning that it breaks down fat quicker. This happens due to the increase of hormone-sensitive lipase (HSL and an enzyme that breaks down fats) and inhibits glycogen phosphorylase (which is the enzyme that is used to break down polysaccharides or carbohydrates in the body. Because of this, there are higher levels of glycogen in the muscles after exercise, which means the body can potentially recover energy faster as these carbohydrate stores have not been depleted. Because of these potentially performance-enhancing aspects of caffeine, it was placed on the World Anti-Doping Association ban list from 1962 to 1972 and 1984 to 2003. It was removed in 2004 but is still monitored by the WADA because of its potential for misuse during competitive sports. Caffeine also causes diuresis, or excessive urination, which is a direct effect on the kidney at the adenosine receptors (similar to the effects in the brain).

Psychological effects of caffeine can range from person to person, depending on their particular caffeine sensitivity, but usually fall into general symptoms. In the Journal of Alzheimer’s Disease, it was shown that caffeine had been associated with decreased depressive symptoms and overall suicide risk. It also can increase alertness and increase emotional arousal (most noticeably in low caffeine users). However, it can work inversely. In larger doses or more sustained use, it has been shown that caffeine can increase anxiety-related symptoms, such as faster breathing, headaches, and increased sweating/pulse rate, and was placed in the DSM-5 as a subclass of Substance-Induced Anxiety Disorder (look for caffeine-induced anxiety disorder). It has also been classified as a potential cause of sleep disorders (reducing the slow-wave sleep in the early sleep cycle as well as a reduction in REM (rapid eye movement) sleep), eating disorders (increasing the metabolic rate and suppressing appetites) and possibly schizophrenic disorders (the adenosine receptors in the brain and the control of dopamine release).

Caffeine is a ubiquitous substance in our daily lives, and has helped many people with school, work, sports and more. But it is important to know the pros and cons of caffeine usage, no matter if you are casual tea drinker or downing multiple espresso shots before shooting out for the day. Always take all foods in moderation.
Fascinating Fridays: The Maillard Reaction

March 10th, 2023

I have a deep love for food and science, and recently I began exploring the connection between the two. How do salt and sugar preserve foods? What creates a bitter taste when foods like garlic cook too long? So many questions pop into my head when slicing vegetables or sauteing over the stove, and I’m sure that we all have had those nagging questions that linger long after our plates are cleared. When recently testing out making oyster mushrooms into mock scallops, I became mesmerized watching the browning occur along the cut edges of the fungi. “What is making it crisp so uniformly? Why does it form a crust in some areas but merely heat the mushroom in others?” With these questions in the back of my mind, I poured into food science articles and videos of chefs flipping French toast and came to find that the science behind this browning has been studied extensively and practiced for as long as we’ve harvested grain. This is the Maillard reaction.

The Maillard reaction is a chemical reaction of the proteins and sugars in a particular food. Unlike caramelization of sugars, or pyrolysis (grilling or toasting of foods where “burnt” portions develop), very specific temperature ranges are needed to begin the rapid process of the Maillard reaction. This range is set between 140 and 160C (280-350F) and is what begins the process that gives us that golden brown, crisp texture on the outsides of our bread and fried foods. The precise science is the carbonyl group (a molecule that contains a carbon and oxygen atom connected via a covalent bond (double-bond)) from the sugar reacts with the amino acids in the food, creating a biochemical compound called glycosylamine and water. Glycosylamine is inherently not stable, so it rearranges itself to become a ketosamine, a more stable molecule that further develops into nitrogenous polymers and melanoidins, the polymers that give food that deep brown color.

The Maillard reaction is not only the reason behind the browning that you see on bread or meats (or even that rich smell of coffee percolating) but also the chemical reaction behind the smells that waft from bakeries and out of your rice cookers. The compound 6-Acetyl-2,3,4,5-tetrahydropyridine is the specific aroma compound that gives bread, tortillas, and other baked items that distinct just-out-the-oven smell. This compound can only be synthesized via the Maillard reaction, which is why mixed/rising dough smells more yeasty and less “fresh-baked”. Almost all of the reactions in the oven that makes bread look and smell so delicious are known to us now due to Louis Camille Maillard, the namesake for the reaction.

Louis Camille Maillard was a French chemist and physician. He primarily worked in the nephrology field, dealing with various ailments of the kidneys, but took interest in the presentation and reactions of amino acids and sugars, especially in foods. He began laying the groundwork in the 1910s for the cause of browning and flavor profile changes in cooked foods but was not the one who ultimately discovered the mechanisms that are described above. That distinction falls to an African American chemist named John E. Hodge. Hodge worked for the United States Department of Agriculture and in 1953 discovered the way that the sugars react with the amino acids, releasing the glycosylamine that undergoes the Amadori rearrangement to produce the browning compounds.

More scientists have delved into the scientific processes involving the Maillard reaction, and have found that even on molecular levels within our bodies the reaction occurs. Sugars that are floating around our blood after eating start Maillard reactions in the form of inflammation responses particularly centered around the cardiovascular and liver systems. Our bodies have developed defense mechanisms (aside from the inflammation response) to remove the by-products of the Maillard reaction, but are effective only up to 99.7% of the time. Those reactants that slip under the fence can begin to cause more serious damage to our bodies over time (for example, cardiovascular disease).

Ultimately, as I sear another mushroom on the stove, I am happy to know a little more about the process that gives my mushrooms that nice crunch and fills my apartment with the smells of a Parisian bakery during weekend afternoons. Just like Maillard over 100 years ago, cooking continues to fascinate and delight people around the world, just like me in my kitchen. I plan to continue these little scientific forays into food once a week and would love to hear some questions from those that are reading that may have popped up when in your kitchens. Always have fun and try to push your boundaries when working in the kitchen, stepping out of your comfort zone and trying a new cooking method or food from a different part of the world. Let me know your new experiences and I’ll see everyone for the next Fascinating Friday where we’ll talk about flavor profiles and why certain foods match so well with others!