Author: ZQSeah

Content

In the fifth and final chapter, I will discuss about Molecular Gastronomy and the Future of Food.

Molecular Gastronomy

From the previous blogpost on the workshop, there are 4 main types of colloidal dispersions: aerosols, emulsions, foams and sols.

Colloidal Dispersions

• Aerosols: Liquid dispersed in gas
• Emulsions: Liquid dispersed in liquid
• Foams: Gas dispersed in liquid
• Sols: Solid dispersed in liquid

These colloidal dispersions are more common than expected and can be found in our everyday lives. Coffee crema, the foam formed from an espresso extraction. Cake batters and mayonnaise, the emulsion between the hydrophilic and hydrophobic molecules. Some of them might have added emulsifiers and stabilisers, as mentioned in the previous blogpost. From the infographics below, emulsifiers such as eggs are used in mayonnaise to stabilise the mixture. However, it is still possible for the mayonnaise to destabilise if it is not kept under proper conditions. I observed this before, where a darker liquid separated from the sauce.

Now let’s look at something different. Agar agar jelly is a common dessert in Singapore, and can be readily found at fruit and dessert shops in local coffeshops or kopitiams.

Agar jelly is a sol of agarose polymers dispersed in water, which can also be considered a gel. Gels are sols in which the solid particles are meshed such that a rigid or semi-rigid mixture results. Cross-linking within the gel’s polymer or colloidal network causes a gel to behave as a solid in its steady-state and makes it tacky and wobbly.

These are main colloidal dispersions we would observe in general, but there are more variants/extensions and complex combinations of these forms such as:

• Solid aerosol: solids dispersed in gas
• Solid foam: gas dispersed in solids

Moving on to something more interesting!

Spherification: Direct & Reversed

Have you ever wondered about the liquid pearls that burst in your mouth after biting into them? If you have tried them before, aren’t they interesting? It is the product of spherification. Depending on the intended outcome, there are two method that can be used: direct and reverse spherification.

There are 2 different key solutions, sodium alginate and calcium chloride, essential for the spherification process. What happens during the process is that the calcium ions will displace the sodium ion on a carboxylic acid group (COO-). Due to the additional charge on the calcium ion, it attracts another alginate chain and keeps them together with the electrostatic attractive forces.

The eventual product depends on which solution is added to which solution. For direct spherification, the pearls formed is a gel throughout. For reverse spherification, the pearls has a thin gel film on the surface, with flavoured liquid enclosed within. Both type of pearls formed must be stored in the same bath to maintain the film. If stored in water, water might diffuse into the pearl and bursting it from within after expansion. There are many other factors such as pH that plays a role, but I will not discuss it here.

Here’s a table to summarise everything.

Direct Spherification	Reverse Spherification
Sodium alginate liquid to calcium chloride bath Gelification occurs to the entire caviar Stored for a shorter time More sensitive to acidic liquids Bath does not require resting	Calcium chloride liquid to sodium alginate bath Gelification occurs only on the surface of caviar Able to be stored for a longer time Less sensitive to acidic liquids Bath requires resting of 24 hrs

Next up, the second half of the chapter: Future of Food!

 

Future of Food

A future of uncertainty

We live in uncertain times with difficult challenges ahead. As humanity enters the Anthropocene with environmental challenges of global warming and climate change, the environment rapidly changed without time to adapt. Oceans become warmer, erratic weather and abnormal climate trends. In the next decades, we may experience a change in our food we eat, the supply we have, and the nutritional value it has.

Growing crops will become more difficult, the nutrition of the crops will decrease, and pollinators such as bees may not be around for long. Warmer surface waters have bleached corals, the living environment for fishes and other marine life obsolete. Animal farming operations for meat such as pigs and cows contribute to significant greenhouse gas emissions and may not be sustainable in the long run.

A future of science and technology

Science and technology has benefited humanity over the centuries with its discoveries and inventions. This is no exception to our global food problem. With the advent of new machines and fresh discoveries, we are able to learn, innovate and create solutions for our problems.

From the reading ‘Planting seeds for the future’, scientists used their understanding of genes in food to edit the characteristics of crops. One prime example is Bacillus therigensis (Bt) crops that have been genetically modified (GM) to be more resistant to pesticides and herbicides, which increase the resilience of crops and food supply. Studies have also shown that iron, zinc and Vitamin A have improved using strategies that uses the genome-assisted plant breeding.

Tapping on existing technology, 3D printing is also being explored for food. In the reading ‘Molecular Gastonomy meets 3D Printing: Layered Construction via Reverse Spherification’, with the rise of molecular gastronomy and understanding how molecules interacts, 3D printed food could be the future of food. Design and manufacturing of the food on demand from these printers could also mean readily accessible food anytime, anywhere. However, there are aspects that still fall short such as texture and replicability that needs more development to achieve unique edible objects.

A future of alternative meat

As animal farming operations contribute to significant greenhouse gas emissions, the future of meat will change in the decades. Alternative meat sources such as plant-based meats are already in the market, and stem cell lab-grown meat are being explored. Soy-based Impossible burgers are available in some restaurants and in supermarkets.

I have tried an Impossible burger when it was made a limited time menu at one of the local fast food chains. The flavour is similar to actual meat patties, but the texture was still far from the actual thing. I hope that there is still room for improvements so that Impossible burgers becomes an everyday option and choice.

A future of alternative sources

In the reading ‘The Meat of Affliction’, insects were explored as an alternative protein source with its lower environmental footprint. Some countries have consumed insects as part of their traditional cuisine such as Angola and others like Thailand or China are also known for their active entomophagy (consumption of insects). What’s interesting is that there are more looking towards insects as their vision for the future, such as Belgium and the Netherlands.

According to the article ‘Edible Insects as a Protein Source: A Review of Public Perception, Processing Technology, and Research Trends’ (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6728817/#B85), on average, the protein content of edible insects ranges 35%–60% dry weight or 10%–25% fresh weight. This is higher than plant protein sources, including cereal, soybeans, and lentils. It is also possible for insects to provide more protein than even meat and chicken eggs. Although it seems gross to consume insects now, someday we might just have it as a primary source of protein.

Conclusion

As we enter the uncertain future with imminent environmental challenges for our supply and sustainability of food, science and technology would advance our understanding and change how we look and produce our food, and innovate on new food and technologies.

 

Content

The fourth chapter brings us to the science of Chocolate and Ice Cream.

Chocolate

Chocolate, one of the popular desserts around the world. Made from cocoa bean, it undergoes a long preparation process from harvest to products in the form of cocoa powder or chocolate.

There are 3 general categories to chocolate: dark, milk and white.

• Dark chocolate has a composition consisting mainly of cocoa particles, cocoa butter and sugar.
• In milk chocolate, significant amounts of cocoa-bean particles are substituted with dried milk proteins and sugar.
• White chocolate has no cocoa in its composition and is made of cocoa butter, milk solids and sugar.

Often you would see chocolate advertised at “70% chocolate”, what they are trying to say is it’s 70% cocoa butter and particles and the remaining 30% is sugar.

Cocoa

Fermentation

So what is cocoa? Cocoa powder and cocoa butter are obtained through the fermentation of cocoa beans. The initial fermentation by lactic acid bacteria produces alcohol, which undergoes another fermentation with acetic acid bacteria that converts alcohol to acetic acid. Acetic acid produced penetrates into the beans and etches holes within the cells, allowing astringent phenolic compounds to react with other molecules such as proteins. This would form less astringent complex compounds, making it more appealing to taste.

Roasting

Dried fermented cocoa beans are less astringent and more flavourful than unfermented beans. After drying, cocoa beans are roasted for 30-60 minutes at 120-160 degC, allowing the Maillard reaction to occur. The abundance of amino acids and sugar present within the cocoa beans generates the rich flavour chocolate has, thus note that the difference in roasting temperature range between cocoa roasting and general Maillard reactions.

Grinding and Refining

After roasting, the cocoa nibs (inner part of the beans) are separated from the bean, and passes through steel rollers to produce a thick, dark fluid called cocoa liquor. Cocoa liquor comprises of 2 parts: cocoa butter and cocoa particles. Refining (also the final grinding process) grinds the particles down to 0.02 to 0.03 mm. (We humans are able to detect solids down to 15 micrometres (which is 1000 smaller than millimetres (mm)!)

The cocoa liquor is pressed against a fine filter that retains the cocoa particles, allowing cocoa butter to pass through. This separation allows for different uses of each component. The retained cocoa particles will stack up into a ‘cocoa cake’ which can be smashed into cocoa powder, which is used in desserts, drinks and more. Cocoa butter can be used for white chocolate, skincare and many other products.

Chocolate Polymorphs

There are 6 different chocolate polymorphs. Polymorphs can be loosely defined as the different forms/structures of the same thing. In this case, all 6 polymorphs can be obtained from the same batch of chocolate, but the preferred form is Form V. Why? Form V has a melting point of 32-34 deg C, has a pretty, glossy shine. It is also the most stable form when stored at room temperature, but still susceptible to changes if not stored properly.

Tempering

Tempering is the physical process where a chocolatier uses a scrape to continuously apply a shearing action on the melted chocolate sitting on a cold marble slab. Does that sound familiar? You might have seen it before:

As the marble surface is colder than the melted chocolate, it will lose heat through conduction. The chocolate in contact with the surface will become cooler, and start to pack together and assemble in an orderly fashion. The action of moving the melted chocolate and mixing it continuously is shearing, where a force is applied perpendicular to the cross sectional area. Now here comes the art and experience of chocolatiers. Insufficient stirring would produce too few seed crystals, and over-stirring would  produce too large seed crystals. Both will result in less than desired product, either melting too easily or coarse and crumbly.

Alternatively you can introduce seed crystals into the melted chocolate, allowing the randomly order chocolate to organise in the same packing as the seed crystals.

Fat Blooming

When chocolate bars are not stored properly, and allowed to melt and freeze again, a layer of white powder can be found on its surface. This white layer is actually cocoa butter! Cocoa butter would melt with the unstable crystals and reform on the surface. If it was properly tempered with no unstable crystals of other forms, this is unlikely to happen. The best temperature to store chocolate is 15-18 degC without any fluctuations for melting and recrystallization to occur. So it’s still safe to eat my chocolate with that white powder layer!

Crystallization

Now you might ask, what’s up with ‘seed crystals’?

Seed crystals are neatly packed solid particles of a certain component. This acts as the starting point for others to build upon, similar to constructing a building starting with a blueprint. Similarly, seed crystals provides the base for the melted chocolate to build upon. By providing the necessary mixing and time, the bulk (most of the chocolate) can follow the packing order of the seed crystal, effectively transforming it into the desired form.

Now with this chemistry concept, it’s a good time to move on to ice cream!

Ice Cream

Similarly, this is how ice crystals are packed when it is being cooled and eventually freeze. Remember being shown the ‘magic trick’ of instant freezing water after knocking it? Here’s a reminder:

Due to the lack of impurities or ‘seed crystals’, there is no nucleation/starting sites for water molecule to start organising and packing. When it is disrupted by hitting it on a surface in the right conditions, water molecules will come together and form an ice nucleating seed crystal for ‘everyone else to follow’. As everyone knows the freezing point of water is 0 degC, but if there is no impurities, it can remain liquid below 0 degC and we call this state ‘supercooled’.

The rate of cooling or freezing process of the ice also affects the size of the ice crystals. The shorter the time of cooling, the less time for the ice crystals to grow, resulting in smaller crystals. The smaller the ice crystals, the smoother the ice cream.

As seen from the graph in the previous section, there is a region of rapid nucleation where new seed crystals are formed. This doesn’t mean that no new crystals are formed after, but rather the preference to grow from the existing ones.

The formation of water to ice is a cooling process, or freezing, where energy/heat is taken out. There are many ways for cooling, from the use of chemicals (liquid nitrogen, dry ice) or the use of machines to remove heat (freezer, anti-griddle). These method have different rates of cooling and produces ice cream of different textures.

Types of ice cream

There are many types of ice cream from sorbet, sherbet to dairy and Turkish. Each and every variation of ice cream is unique, but there are too many intricate details to discuss. Here we shall discuss 2 common types of ice cream:

1. Sorbet
   Sorbet contains no milk or dairy products. It is generally prepared from a thick, flavoured solution. It is then freezed before serving. Effectively, it is flavoured solid ice.
2. Dairy Ice Cream
   This is the most commonly available type of ice cream. It contains dairy/milk or cream and sugar, flavourings, colourings and sweeteners. The mixture is normally stirred before freezing to introduce air into the thick mixture, essentially forming a combination of foam and emulsion (will be explained later).

   Generally, the common ingredients are:
   – Milk (proteins): the main ingredient to stabilize emulsions and foams. Can be whole milk, skimmed milk or condensed milk; each has different fat %.

   – Sugar: the essential sweetener in our ice cream! Examples: glucose/dextrose, fructose and sucrose.

   – Oils & Fats: Helps to stabilize the foam formed that provides the creamy texture. Examples: Milk fats!

   – Water: 60-72% weight/weight of ice cream! The main component that mixes everything together.

   – Emulsifiers: to stabilize the air bubbles in ice cream, giving that aerated texture. Examples: egg yolks and mono/di-glycerides (fatty acids)

   – Stabilizers: reduces the rate of melting, slows down the migration of moisture in ice cream during storage. Examples: Xanthan, gelatin and sodium alginate.

* Fun fact: Total solids in an ice cream refers to everything else other than water!

Coarsening

Coarsening is a process where the size of particles increase at the expense of total number of particles. There are 2 ways this can happen:

1. In emulsions and foams (this will be explained in the next section), it is called coalescence. For ice crystals, it is called accretion. Coalescence and accretion is the process of two or more adjacent particles join to form a larger one, or simply combining.
2. For ice crystals and emulsions, it is called Ostwald ripening. For foams, it is called disproportionation. Ostwald ripening and disproportionation is the transfer process from smaller particles to larger particles by diffusion, or giving and receiving.

Remember when the ice cream becomes ‘freezer-burn’ where it just becomes too icy and chunky? There could be 3 possible reasons:

1. Recrystallization of melted ice cream: the water and milk fats in the ice cream separated when it is melted and recrystallize when freezed, forming large solids that spoils the good texture it once had.
2. Ostwald ripening of ice crystals: the slow natural rearrangement of ice crystals, forming larger ice crystals that gives that coarse mouthfeel when consumed.
3. Condensation of water vapour in the headspace of the ice cream tub: the empty space above the ice cream can be called headspace. When placed back in the freezer, the water vapour condenses on the surface on the surface of the ice cream.

(Tip! I read somewhere that you can avoid #3 if you store your ice cream upside down, effectively condensing the water vapour on the lid instead.)

Workshop

In Week 7, we conducted our own workshop under the guidance of Dr Linda Sellou.

Colloidal Dispersions

There are 4 main types of colloidal dispersions: aerosols, emulsions, foams and sols.

• Aerosols: Liquid dispersed in gas
• Emulsions: Liquid dispersed in liquid
• Foams: Gas dispersed in liquid
• Sols: Solid dispersed in liquid

Chocolate Mousse

Each group was picked their chocolate randomly by drawing lots and every chocolate brand was advertised to contain at least 70% cocoa. We broke our chocolate apart and melted it down using a warm water bath, continuously stirring it.

By introducing air while stirring, air is trapped and dispersed within the melted chocolate while it cooled. This forms a foam (dispersed gas trapped in a continuous liquid medium). This gives a fluffy, aerated texture in the mouth. Due to the use of dark chocolate, it may not be appealing to all as it has a bitter taste.

Ribena Sorbet

Sorbet is not really a colloidal dispersion, but a rapidly cooled frozen solution. We took dry ice (solid carbon dioxide) and crushed them into smaller sizes before adding to a concentrated Ribena solution. Rapidly stirring the concentrate, the water in the Ribena solution freezes and forms small ice crystals. This gives the sorbet a smooth, slushy texture when eaten.

* Tip! Use more ribena syrup if you are trying it out 🙂 A sweeter mixture gives a better tasting sorbet.

I had a blast attending this workshop, trying the various chocolate mousse and Ribena sorbet that different groups made.

Conclusion

The core theme between chocolate and ice cream is the cooling process, which significantly affects the shape, size and/or texture of the final product. I have learnt so much about chocolate and ice cream from their composition, their preparation process, the chemistry behind, even down to their storage conditions.

There’s really too much science that can be discussed in great detail. I hope that I have sufficiently picked out the primary ones that are easily understood!

NEXT: Last chapter, Molecular Gastronomy and the Future of Food!

Content

The third chapter Baking & Cooking covers the chemistry and science behind of baking and cooking processes.

Baking

There are many ingredients that can be varied for different flavour and textures of baked goods, from cookies and breads, to macarons and cakes. I will be focusing on breads as it is the simplest baked goods to discuss in detail here. There are 4 general factors to making breads:

1. Flour & Water
   The ratio of flour to water ratio determines what is it called. If the mixture is predominantly flour, it is a dough. If the mixture is predominantly water, it is called a batter. Doughs are used for making breads while batters are used for making crépes, and griddle cakes (pancakes).When the flour is mixed with water and kneaded, the randomly oriented glutenin molecules forms a network of gluten chains. Repeated kneading helps to stretch and elongate the gluten chains by forming strong chain end-to-end bonds. This produces a stretchy and elastic final product. If the dough is over-kneaded, the dough becomes sticky and inelastic.Kneading also introduces air into the dough by forming small trapped air pockets. The more pockets formed, the finer the texture of the final bread.
2. Salt
   Salt is added 1.5-2% of the flour weight, to help tighten the gluten network and improve the final volume of the loaf. The sodium and chloride ions cluster around the charged regions of the glutenin proteins, preventing them from repelling each other.
3. Leavening agent
   There are 2 types of leaveners, microbiological (yeast) and chemical. Yeast consumes sugars in the dough to produce carbon dioxide in the gluten network, forming small air pockets and increasing the volume of the dough (refer to my post on fermentation, on how yeast works). Doughs using yeast for rising would need to incubate the yeast in a warm environment for a few hours before baking the dough.The other method is chemical leavening. No, it’s not something artificial and unhealthy. It works via the chemical reaction between an acid and a carbonate (a base), which releases carbon dioxide. Baking soda is chemically known as sodium bicarbonate (NaHCO3), which would react with an acid such as buttermilk or citric acid. Baking powder is a mixture of sodium bicarbonate and tartaric acid (cream of tartar; can be found naturally in fruits such as grapes), which only requires water to initiate the acid-base reaction. Much simpler, eh? However, that depends on what ingredients the baker wants to use.

Of course, nonetheless we have the actual baking process where the magic happens. When introduced into a pre-heated oven, the moisture within the dough vaporizes and the dough expands and rises. After 6-8 mins, the gluten molecules would start to form strong cross-links and forms a rigid structure that does not stretch. The air pockets within the rigid structure can no longer stretch and would rupture forming the open network of pores that you see in the final product. Over time, continued baking would result in surface browning, forming the bread crust and develops the flavour. This process is also known as the Maillard Reaction (covered in the next section; read on!).

That’s a summary of how bread is made! I wish to talk more in detail about other baked goods but it will be too long.

Fun fact: Biscuits and cookies can become soft and ‘airy’ if not stored properly. This is due to the absorption of moisture from air by the sugar in the biscuit. This can be reversed by toasting or baking it at a sufficiently high temperature and time to remove the moisture within.

How you say? Let’s talk about cooking methods.

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Cooking

As a Chemistry major, we learnt about the interactions between the electromagnetic radiation and molecules. Scientists uses these intrinsic characteristics based on quantum physics and chemistry to investigate the structures of compounds of interest. On the other hand, we use it everyday to prepare and cook food.

Don’t be intimidated by the diagram 🙂 As you might remember from your science classes, atoms and molecules rotate and vibrate in the fixed positions. When the energy of the electromagnetic radiation coincides with the required energy, the molecule absorbs the energy and achieves a higher energy state, similar to fitting a key in the right keyhole. The molecule would then relax and release this energy in the form of heat. This is why your frozen food would heat up after spinning around in the microwave. Generally, what would be commonly used for food preparation are microwaves and infrared radiation.

Microwave radiation coincides with the energy for molecules to rotate, while infrared radiation coincides with the energy for molecules to vibrate. As chemical reactions occur between molecules when their bonds break and form new bonds, they would first need to stretch beyond its limits and snap apart. Infrared energy is responsible for this process and can be observed while barbecuing food, where hot burnt charcoal releases heat in this form. (This is due to a phenomenon called the Blackbody Radiation). However, chemists would understand that only polar molecules would absorb infrared energy.

This is a good time to transit into the cooking processes. Moving on!

Processes

Caramelization

Caramelization is the process where any sugar (glucose, fructose, sucrose, etc.) are heated and the structure starts to break apart. The broken sugars form hundreds of new compounds of varying taste and aroma. The longer a sugar is cooked, the less sugar and sweetness remains, the darker and bitter it becomes.

(Insert glucose, fructose and sucrose molecules)

Glucose and fructose are referred to as “reducing sugars”, in which they are easily oxidized and reduces other compounds, making them more reactive. Sucrose is made of 1 glucose and 1 fructose molecule bonded by an alcohol group, hence making less reactive than its constituent sugars. This is why sucrose requires a higher temperature for caramelization (170 deg C) than glucose (150 deg C) or fructose (105 deg C). This is the same process occurring when the cookbook or video asks you to caramelize your onions.

 

Maillard Reaction

The Maillard Reaction occurs between a carbohydrate (a sugar) and an amino acid, forming an unstable intermediate product before further forming hundreds of different by-products. A brown colouration and full, intense meaty flavour will be produced.

Maillard flavours are more complex and meaty than caramelized flavours (in the next subsection) due to the involvement of amino acids containing nitrogen and sulfur atoms, introducing whole new possibilities for new families of molecules.

This is the process occurring during the cooking of meat at barbecues, where Maillard reactions can take place temperatures below 100 deg C. Thus, in general, Maillard reactions occurs at lower temperatures, while caramelization starts at higher temperatures.

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Workshop

This week, we had a self-directed Pancake workshop. There were two pancakes, one souffle and one western. Both similar in their ingredients but their amounts varied.

The goal was to observe and investigate the role of ingredients, the amount of ingredients, and the preparation process. My group got the western pancake recipe, which was significantly easier than the souffle style. The souffle style would required to foam egg whites till peaking is observed. A foam is essentially gas (air) dispersed through a liquid (egg white). This allows the final souffle to have a light, fluffy mouthfeel after the pancake batter solidifies.

As mentioned earlier, baking powder is added to allow carbon dioxide to be produced without a need of an additional acidic ingredient. This also introduces air pockets within the batter that makes final product slightly more fluffy, but still varies significantly from the souffle style.

The cooking of the pancake also gives it that beautiful brown colour, which is likely the Maillard reaction occuring as the temperature of pans would not reach the high caramelization temperatures of table sugar (glucose).

We had fun eating our pancakes with maple syrup and milk 🙂 It was a fun workshop and to see people cooking outside the library for the first time.

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Sorry that this blog post is kinda lengthy~ Hope you enjoyed reading it 🙂

Next chapter: Ice Cream & Chocolate!

 

Content

The second chapter Brewing and Fermentation covers the chemistry of coffee, tea and beer brewing, and fermentation of food and beverages.

Brewing

To continue with my previous post, the Coffee Roaster workshop introduced the brew parameters of coffee. This week, with the online videos and readings, I deep-dived into the science of coffee brewing.

There is a ‘Goldilocks’ set of brew parameters to ideally get a good cup of coffee. In general, there are 6 brew parameters:
1) Water quality – this includes water hardness, acidity/pH, cation composition. All of these can influence the overall result of the coffee extract. As we know that there are many compounds in coffee, each with their own pKa and related chemical properties such as solubility.

2) Temperature – it represents the average kinetic energy of water molecules. The higher the temperature, the more able these molecules may penetrate the interstitial (between ground coffee particles) and interstitial (within the ground coffee particles) spaces of the coffee grounds. This also affects the solubility of compounds, affecting the overall flavour profile of the coffee. The recommended brewing temperature for hot coffee is 91 – 94 degC.

3) Particle Size/Grounds Size – the smaller the coffee grind size, the higher surface area for the extraction of compounds to take place, leading to higher concentration of compounds

4) Brew ratio – this is referred to the final coffee grounds to water ratio by mass. This affects the overall concentration of the compounds in the final cup. Espresso

5) Pressure – the higher the pressure from the espresso machine, water is better able to penetrate into the intrastitial spaces of the coffee ground, extracting the flavour compounds better.

6) Time –  time depends on the method of brew and the 5 other brew parameters above. The longer the coffee grounds are immersed in/exposed to water, less soluble compounds may be extracted over longer periods of time.

There are other brew parameters but will not be discussed in detail here. These brew parameters may be applicable for tea brewing as well.

According to ‘Chapter 15: The Brew – Extracting for Excellence’, if coffee is extracted at too low temperatures, the acidity and sweetness will remain the same while the aroma (volatile compounds) and bitterness (phenylindanes, chlorogenic acid, lactones, etc.)  will be lacking.

There are many details that a chemist would greatly appreciate and understand the intricacies shared in the readings that others might not fully grasp or understand.

My favourite beverage is cold brew, due to its ideal non-bitter, non-astringent taste if prepared and stored properly. It has the taste similar to iced americano, but without the bitter aftertaste. By immersing coffee grounds in cold water, it lacks the heat to extract some less polar compounds such as coffee oil. Thus, a longer extraction time was required for the flavour compounds to diffuse out of the coffee grounds. As mentioned in the reading, cold brew coffee “emphasizes on body, sweetness, and chocolate notes, and have a syrupy characteristic.” Long brewing times and improper storage conditions will lead to oxidized flavours in the cup, making it more sour/acidic.

Reading and learning about coffee makes me understand the western coffee menu better, like those in Starbucks or at cafes.

This led me to think about the preparation method of Chi Cha San Chen, a Taiwan bubble tea chain in Singapore. They use the espresso method of pressure extraction of tea leaves for their drinks, leading to a fresh cup of extracted tea. An interesting fact is that white tea, green tea, oolong tea and black tea can be prepared from the same harvested tea leaves. Their difference lies in the preparation process, namely drying, bruising, roasting and fermentation and this brings me to the next topic, fermentation.

Fermentation

Fermentation is defined in 2 ways:
(1) the microbial conversion of glucose to ethanol or;
(2) the natural browning reaction catalyzed by enzymes from the tea leaves.

The fermentation of wine, beer, tea, kimchi, kombucha, etc. refers to the first definition of fermentation, the more commonly known definition. The second definition refers to the preparation process of tea: withering, rolling, fermentation and roasting. Withering removes moisture and concentrates the compounds in tea leaves; rolling bruises and damages the tea leafs and allow oxidation of the compounds to occur; fermentation transforms the polyphenols of green tea leaves into more complex polyphenols in black tea and lastly; the roasting process, to stop the enzymatic activity and ends the tea preparation process.

The primary fermentation (1) is the ‘fermentation’ process everyone knows it to be. The microbial conversion of glucose or sugar in presence of oxygen into ethanol and carbon dioxide.

Workshop

In Week 4, the fermentation workshop focused on kombucha, a fermented tea. The workshop was conducted by Ding Jie, founder of Starter Culture and a NUS MSc Food Science alumni.

He introduced the concept and science of fermentation by microorganisms, and it is used a lot, including miso, natto, sourdough, and even tempeh! Interesting 🙂 He went in-depth about fermentation microbiology, the type of culture used, the aerobic and anaerobic air exchange, and chemical changes during fermentation.

In this workshop, he focused on the fermentation of kombucha. He explained that lactic acid bacteria (LAB) and acetic acid bacteria (AAB) converts sugars to lactic acid, and acetic acid and cellulose (pellicle) respectively, providing that sour taste in kombucha. Yeast was added to convert sugar to ethanol.

Carbonation drops, unfermented kombucha in the jar, fermented kombucha in the bottle.

Both the jar and bottle were brought home for the next step. After putting a kitchen towel over the jar, it was left to sit for a week. The porous kitchen towel allows oxygen to enter the jar and allow the yeast to start doing its work and ferment. Over the week, I observed the primary fermentation of kombucha, the aerobic process occuring in the jar.

He went on to share the chemistry and application of the general fermentation process, in yoghurt, Chinese red rice wine, hot sauce, mead and amazake. Fermentation sure is widely used in food and beverages!

Pictures taken over a week, to observe the fermentation of kombucha, with the cellulose pellicle building on the surface of the tea. 

The secondary fermentation process, or the anaerobic process, occured in the bottle. Carbonation drops were added to make the fermented kombucha in an airtight bottle to make it fizzy. The carbonation drop, composed of glucose and sucrose, was added to allow the anaerobic process to begin. When first opened, the pressurised water vapour in the headspace above the bottle suddenly condensed, forming a cool misty smoke effect 🙂

Next week: Baking & Cooking! We are making pancakes on Valentine’s Day for our workshop! Can’t wait 🙂

Content
Weeks 1 and 2 were focused on the introduction to the module, setting up the stage for the future topics by recapping and covering chemistry concepts through online videos and readings. This includes chemical bonding of the molecules in food, physical chemistry, relevant thermodynamics such as phase diagrams, and calculations such as pH and water hardness (the amount of metal ions in our water supply/tap water).

In our reading ‘Chapter 15: The Four Basic Molecules’ of Harold McGee’s On Food and Cooking, the four basic molecules of food are 1) water, 2) lipids, 3) carbohydrates, and 4) proteins.

One common misconception are lipids. Lipids are hydrophobic molecules with long carbon-chains, and common names like fats, oils and fatty acids are classified under lipids. Some examples are beta-carotene, the molecule responsible for the orange coloration of carrots; vitamin E and cholesterol, a ‘dangerous’ molecule in high levels will result in heart disease.

As the saying goes ‘Too much of a good thing is a bad thing’, everything should be in moderation, including moderation.

Fats and oils triglycerides, molecules that linked together on a short backbone called glycerol.  There can be up to three fatty acids that can be linked to glycerol. These triglycerides can be hydrolyzed, breaking it down to glycerol and fatty acids. Fatty acids can be saturated (sp3 carbons) and unsaturated (sp2 carbons).

Poly-unsaturated omega-3 fatty acids from fish are healthy fats due to their structures. As they are ‘curled’ and kinked up due to their alkene conformation, they are unable to fit and interact nicely together.

This is also why some meats can be kept longer than others. Beef have more saturated fatty acids compared to chicken, pork, or lamb, thus a longer shelf life as they are less susceptible to atmospheric oxygen oxidation.

In another reading ‘Chapter 3: Taste’ of Hérve This’ Note-by-Note Cooking, I learnt about the term ‘sapid’. A compound can be considered sapid if they bind to a receptor. But taste can appear if two small molecules work together to bind to two parts of a receptor.

I also got to learn about the many common chemical compounds and molecules hidden in daily food and beverages added as additives for various purposes. They are common labeled as E (number), and the first number classifies them into a certain category. ‘2’ belongs to the acids, and E260 is acetic acid or vinegar taste; ‘6’ belongs to the ‘Flavour Enhancers’, and E621 is the widely known monosodium glutamate (MSG); and ‘9’ belongs to the sweeteners, with E951 is aspartame commonly found in diet soft drinks as a sugar substitute. It helps to know what these ‘E’ additives are with a simple online search, and I hope that others taking this module would appreciate this information too.

Workshop
As part of our face-to-face tutorials, the module utilizes hands-on experiential learning through workshops. Our first workshop was a coffee appreciation workshop conducted by Swee Heng, the co-founder and director of The Coffee Roaster, a NUS alumni who opened his own café at AS8 in NUS.

He had us taste 2 different coffees, one from Brazil and one from Ethiopia, and have us described the aroma and taste profile of each coffee.

After that, Swee Heng gave us a lecture on coffee knowledge and appreciation, before covering coffee extraction theory in detail.

He covered the difference between Arabica and Robusta coffee species, one used for cafés and the other in local coffeeshops ‘kopitiams’ respectively. Probably Ya Kun uses Robusta, which is commonly known as Nanyang coffee as well. He provided us an introduction of the coffee belt in the Tropics, which has the conditions for growing coffee. Before moving on to extraction theory, he covered some common myths and facts of coffee.

For the extraction theory lecture, he covered the fundamental brew parameters such as water hardness, brew ratio, coffee grind size, brew time, brew temperature, and extraction pressure.

Just to briefly touch on some examples: brew ratio is defined as the mass of coffee to mass of the final drink. Risettro has a 1:1 ratio; Normale is 1:2; Lungo is 1:3; and a pourover is 1:14 or 1:17. This affects the overall concentration of compounds in the cup, affecting the overall taste profile of the extracted coffee.

Coffee grind size also affects the extraction of compounds from the coffee beans. The smaller the grind size, the more able water would be able to permeate the interstitial (between ground particles) and interstitial (into ground particles) sites of the coffee ground, extracting the soluble compounds out into the drink.

These are just two of many brew parameters affecting the profile of the coffee beverage.

I will cover more of these parameters in detail for Chapter 2 – Brewing and Fermentation.

Class photo in Week 1 Thursday, 16 Jan 2020, for our first class together. 

Looking forward to the next workshop on the topic of fermentation!