Physics and Chocolate by Year 12 Physics Students

‘‘Chocolate Unwrapped’’ Trip Report by Pameer Saeed


This report will describe how chocolate companies make chocolate, what conditions are necessary and how these are used in order to produce sweet and delicious chocolates.

History of Chocolate

When most of us hear the word chocolate, we picture a bar or a box of chocolates. The verb that comes to mind is probably "eat," not "drink," and the most apt adjective would seem to be "sweet." But for about 90 per cent of chocolate’s long history, it was strictly a beverage, and sugar didn’t have anything to do with it.

"I often call chocolate the best-known food that nobody knows anything about," said Alexandra Leaf, a self-described "chocolate educator" who runs a business called Chocolate Tours of New York City. The terminology can be a little confusing, but most experts these days use the term "cacao" to refer to the plant or its beans before processing, whilst the term "chocolate" refers to anything made from the beans. "Cocoa" generally refers to chocolate in a powdered form, although it can also be a British form of "cacao."

Etymologists trace the origin of the word "chocolate" to the Aztec word "xocoatl," which referred to a bitter drink brewed from cacao beans. The Latin name for the cacao tree, Theobroma cacao, means "food of the gods."

Many modern historians have estimated that chocolate has been around for about 2000 years, but recent research suggests that it may be even older.

"Who would have thought, looking at this, that you can eat it?" said Richard Hetzler, executive chef of the café at the Smithsonian’s National Museum of the American Indian, as he displayed a fresh cacao pod during a recent chocolate-making demonstration. "You would have to be pretty hungry, and pretty creative!"

It’s hard to pin down exactly when chocolate was born, but it’s clear that it was cherished from the start. For several centuries in pre-modern Latin America, cacao beans were considered valuable enough to use as currency. One bean could be traded for a tamale, while 100 beans could purchase a good turkey hen, according to a 16th-century Aztec document.

Sweetened chocolate didn’t appear until Europeans discovered the Americas and sampled the native cuisine. Legend has it that the Aztec king Montezuma welcomed the Spanish explorer Hernando Cortes with a dinner that included drinking chocolate, having tragically mistaken him for a reincarnated deity instead of a successful invader. Chocolate didn’t suit the foreigners’ taste buds at first. One of the spaniards described it in his writings as "a bitter drink for pigs" – but once mixed with honey or cane sugar, it quickly became popular throughout Spain.

By the 17th century, chocolate was a fashionable drink throughout Europe, believed to have nutritious, medicinal and even aphrodisiac properties. But it remained largely a privilege of the rich until the invention of the steam engine made mass production possible in the late 1700s.

Making Chocolate


There are many steps involved in the making of chocolate, with each playing an important role in the quality of taste and texture of the final product. The journey begins during harvesting and fermentation, which happens on the spot within 24 hours of the pods having been opened, and can take up to 8 days depending on the variety. Fermentation produces the flavour precursors by reducing sugars, glucose and fructose, and amino acids.


Cocoa pods in various stages of ripening

Cacao drying square in front of church,Chuao, Venezuela


Woman drying cocoa


Cocoa beans in a cacao pod

Next the beans are washed and dried, which can last for weeks, until they have been rendered immune to further microbial deterioration or decay. They are cleaned once again and packed in sacks for storage and shipping, which must adhere to strict conditions to avoid any damage or decomposition.

After this, It is now up to the chocolate maker to continue the process that brings out the flavour and create fine chocolate. By gently roasting the beans, they are further dried and browned and their full flavour is released. Once again roasting requires skill and precision in order to ensure the ultimate quality of the final product. Up to this stage, the beans will still have a shell, which needs to be removed by sifting and winnowing. The more of the shell that is removed, the better the quality of the chocolate will be.The beans are then crushed and milled to reduce them to even finer particles before the refining process converts the milled particles into liquid cocoa mass.


Cocoa beans before roasting


A roasted cocoa bean, the papery skin rubbed loose.

After grinding the mass down further, it is ready for conching – a process of rolling and spreading the mixture to and fro against a hard surface. This releases the cocoa butter, makes the consistency smoother and more liquid and improves the flavour by removing undesirable and unwanted flavours such as acids and astringents and aldehydes. Depending on the desired quality of the end product this process can take several days.

The final step is known as tempering – the art of transforming liquid, or semi-liquid, chocolate in to a glossy, crunchy chocolate with a hard snap. A very delicate process, which involves gently cooling and heating the chocolate and requires skill and experience.


Cocoa butter on the left.                                     Cocoa powder  

Once the chocolate has been properly tempered, it is ready for moulding, pouring and enrobing.


Cocoa powder is ready to make the chocolate seen above

To have a better taste and quality chocolate, there are several conditions and properties that have to be achieved. Some of the conditions and properties are:

Quality of cocoa beans is the first important point, quality of cocoa beans depends on the place and conditions where it grows. Cote d’lvoire which is in Africa produce the best quality cocoa beans in the world. The table below shows top 8 countries which produce most of cocoa beans;



The amount produced

Percentage of world production

Côte d’Ivoire

1.23 million tons



730 thousand tons



490 thousand tons



210 thousand tons



210 thousand tons



165 thousand tons



130 thousand tons



32 thousand tons


Time is also important for chocolate making companies as a better quality chocolate may take several hours or days to make.

Temperature is also important. First sugar and acid is added to cocoa and then heated to get cocoa butter and cocoa powder. Then the resulting powder is heated with some other liquid to get a liquid chocolate. The temperature affects the viscosity of chocolate. The higher the temperature the lower the viscosity and the greater the flow rate. If a sweet manufacturer wants to account for variation in a recipe (which might come from something as minor as a change in supplier of cocoa beans), they can adjust the flow rate by altering the temperature. Viscosity is directly related to fluid temperature.

Viscosity of chocolate is also important for chocolate making companies if they want to produce a chocolate which has some filling. Viscosity is the thickness of the liquid chocolate. The higher the viscosity (fluid viscosity ) the thicker the chocolate you get which then allows you to make a chocolate filling and you can mix it with other flavours. But as the viscosity decreases the chocolate becomes thinner and you can use it to cover the sweet.

To get a pure chocolate flavour, companies used chocolate which has a higher viscosity and to get just a little taste of chocolate and mix it with some other flavours such as strawberry they used chocolate with lower viscosity. In the market both have demand, some people like pure chocolate but some other like just a little taste of chocolate.

Is chocolate healthy or unhealthy?

Dark chocolate is good for your heart. A small bar of it everyday can help keep your heart and cardiovascular system running well. Two heart health benefits of dark chocolate are:

· Lower Blood Pressure: Studies have shown that consuming a small bar of dark chocolate everyday can reduce blood pressure in individuals with high blood pressure.

· Lower Cholesterol: Dark chocolate has also been shown to reduce LDL cholesterol (the bad cholesterol) by up to 10 per cent.

Chocolate also has some other benefits apart from protecting your heart:

· It tastes good

· It stimulates endorphin production, which gives a feeling of pleasure

· It contains serotonin, which acts as an anti-depressant

· It contains theobromine, caffeine and other substances which are stimulants

Chocolate also has some negative effect on environmental and social life.

· Obesity: some companies produce chocolate which has a higher amount of fat, it has an effect on social life and it can increase obesity.

· Temperature: some companies use high temperatures to get fast flowing chocolate, so the the pollution this produces can affect global warming. ( Negative points are taken from different sources and not from the book.).


1. Source (Magazine): Smithsonian

Internet link: (11:17 29/10/2012

2. Source (internet) link : (00:50 30/10/2012)

3. Source (Book): The chocolate Therapist: A User’s guide to the extraordinary health benefits of chocolate by Julie Pech (2010)       

Internet link: onepage&q&f=false

Internet link: onepage&q&f=false

Internet link: onepage&q&f=false

4. Table source:

Chocolate report by Manikandan Jayakanthan

In this report I will be taking a look at the importance of physics in and the historical background of chocolate making. This report will also explain what “viscosity” is and how this is relevant to making chocolate. To understand more about chocolate making I visited the “Chocolate unwrapped” exhibition at the London film museum in Covent Garden.

History of chocolate


The earliest record of chocolate was over fifteen hundred years ago in the Central American rain forests, where the tropical mix of high rain fall combined with high year round temperatures and humidity provided the ideal climate for chocolate plants to grow, such as the Cacao Tree.

The first chocolate factories were opened in Spain using beans brought back from the new world by the Spanish treasure fleets and by the early 17th century chocolate powder was being made for the European version of the drink and was being exported to other parts of Europe. The Spanish kept the source of the drink a secret for many years. The chocolate was so expensive at that time that it was worth its weight in gold. Chocolate was a Treasure Indeed!

The first Chocolate House in England opened in London in 1657 followed rapidly by many others. Like the already well-established coffee houses, they were used as clubs where the wealthy and business community met to smoke a clay pipe of tobacco, conduct business and socialise over a cup of chocolate.

Summary of chocolate and physics

Physics plays a part in everyone’s favourite treat – chocolate. One of the reasons that chocolate is incredibly good to eat is that its melting point is just below body temperature. When you place a piece of chocolate on your tongue it immediately starts to melt, spreading the sweet, satisfyingly fatty taste across your mouth. Chocolate also contains chemicals such as caffeine and theobromine which are thought to contribute to that feel-good lift that keeps chocolate addicts coming back for more. Chocolate can behave in a rather strange way when heated and cooled. If you’ve ever cooked with chocolate you may have found that once heated and then cooled it takes on a dull appearance rather than the glossy smooth texture that it started off with. This is because the structure of chocolate can change when heated.

The visit to chocolate factory (Chocolate Unwrapped)


“Chocolate Unwrapped” was the ultimate occasion for chocolate lovers and was the perfect opportunity for a spot of decadent indulgence. Imagine everything you’d expect to see at a chocolate festival. Chocolate sculptures, cooking demonstrations, tastings, chocolate art and most importantly chocolate making. On the 13th of October we visited the chocolate factory held in the London Film Museum; over 60 chocolate companies were there, including some of my favourite chocolate shops in London: Hotel Chocolat, Paul A Young and William Curley. There was a good line up of demonstrations from top chocolatiers on how to make chocolates and chocolate-inspired foods. I was particularly excited by a demonstration on how to make goat’s cheese ganache on sea salt wafers with lemon, black pepper and gold leaf from Rococo.

The Importance of Physics in Chocolate making

Chocolate making is based on physics. The altering of these physics factors can affect the cost, time and therefore profit. From the flow of chocolate during the product to the cross-sectional area of the chocolate is all based on physics. In addition the time it takes for the chocolate to dry is also dependant on physics principles.

How does physics affect chocolate making and what is Viscosity in Chocolate making?

Viscosity is the liquid consistency (how thick it is in a liquid state or how well it flows). It is based on water, with water having a viscosity level of 1 and each number above is how many times thicker or more viscous than water the liquid is. So 30 viscosity is 30 times the thickness of water making it a thin chocolate formula. 125 Viscosity is thick, making it ideal for moulding and other applications where you want a thick/firm chocolate. When manufacturing chocolate, if you decrease its temperature its viscosity will increase. In the production of chocolate the temperature must be average so that it flows quickly while being produced. There is also a commercial advantage to this as, if the viscosity is average and flowing at a quick rate then, it will require a smaller amount of chocolate to cover the biscuit and sweets, but sometimes the viscosity must also be viscous enough to be moulded to the desired shape.

When a liquid is able to move quicker it is less viscous. If the cross sectional area of the chocolate is greater the force required to break the chocolate piece is greater.


What is a Chocolate crystal?

One of the main ingredients of chocolate is cocoa butter which has a crystaline structure. When chocolate is heated and then cooled, the cocoa butter sometimes recrystalises with a different structure giving the chocolate a dull, matt and sometimes chalky appearance. This can cause major problems for chocolate manufacturers as it makes the chocolate look less appetising. So to prevent it, chocolate goes through a process called tempering – it is heated up, then rapidly cooled and then gently warmed again. This forces the cocoa butter to crystallise with the smooth glossy structure that we all find appealing. In fact, knowing when the wrong crystal structure is forming is tricky, but imaging techniques such as ultrasound can help identify when these changes are going to take place.

Here is a table showing properties of each type of chocolate crystal


Melting temp.



17 °C (63 °F)

Soft, crumbly, melts too easily


21 °C (70 °F)

Soft, crumbly, melts too easily


26 °C (79 °F)

Firm, poor snap, melts too easily


28 °C (82 °F)

Firm, good snap, melts too easily


34 °C (93 °F)

Glossy, firm, best snap, melts near body temperature (37 °C)


36 °C (97 °F)

Hard, takes weeks to form

Making chocolate considered "good" is about forming as many type V crystals as possible. This provides the best appearance and texture and creates the most stable crystals, so the texture and appearance will not degrade over time. To accomplish this, the temperature is carefully manipulated during the crystallization.

Environmental/ Social Context

Producing smooth chocolate affects the environment. Maintaining the temperature, produces greenhouse gases which causes global warming. Also, lowering or increasing the temperature, will increase the cost to maintain it. This will result in the product costing more than it should.

Implications of Physics in Chocolate making

The chocolate’s temperature can result in the chocolate being smooth and less viscous, but is dangerous when handling as hot liquids can result in injury. Also improvement in technology allows us to measure viscosity of the fluid but since chocolate is not transparent and is dark, it will be very difficult to measure the viscosity. Therefore, viscosity of chocolate can only be measured by attaching a straw of a known length to a ball bearing in a falling ball viscometer, which will be used to find the terminal velocity (=distance/time). Terminal velocity is related to viscosity.

Experiment for measuring the viscosity

To test how viscosity affects the flow of chocolate, I did an experiment using honey and syrup. This experiment showed how different viscosities affected the flow of the liquid. I placed a transparent oven dish lid with 18 cm diameter and I placed a scaled paper beneath the dish to measure the honey flow. I used 50ml of honey and measured how long it took to cover 5cm.

These are the results


Spread /Cm

Time / Sec

Honey at 24c



Syrup at 24c



As we can see that the syrup took less time compared to honey to spread a length of 5cm, this tells us that syrup is less viscose that honey.

Below are the links to a video I took at the exhibition

Chocolate Report by Aslam Sookia

I carried out a visit to learn about the physics involved in chocolate making.

The venue for the “Chocolate unwrapped” exhibition was the London Film Museum. Other sources I used for this report are: and

During the visit I asked some chocolatiers how their chocolate was made.

Firstly the cocoa pods are harvested and the coca beans removed. Each pod contains about 30 beans. For high quality chocolate the beans are sun dried for 6-7 days. The beans are then graded by size, and roasted. The size and amount of time the beans are roasted for affect their final flavour. The husks of the beans are then removed, and the ‘nibs’ (kernels) are then put through an alkalisation process to develop the flavour and colour. The nibs are then split into two separate ingredients; cocoa butter and cocoa liquor.

The cocoa liquor is blended with cocoa butter to make different types of chocolate.

Plain Dark Chocolate contains:

70%+ Cocoa solids (cocoa mass and cocoa butter), 29% sugar, vegetable Lethicin and Vanilla.

Milk Chocolate contains:

40% Cocoa Solids (cocoa butter and cocoa mass), 37% sugar, 20% whole milk powder, Lactose, vegetable Lethicin and Vanilla.

White Chocolate contains:

49% sugar, 33% cocoa butter, 18% whole dried milk and whey powder, vegetable Lethicin and Vanilla.

The recipe varies among different manufacturers.

The blended Chocolate then goes through a refining process involving heavy rollers. This grinds down, smoothes and blends the particles to improve the texture. Most of the time, the chocolate goes through a process called ‘conching’. A conch is a type of container in which the refined and blended chocolate mass is continually kneaded and further smoothed. The finest chocolate is conched for at least a week. After the process is completed the chocolate is stored in heated tanks at about 46°c, ready for the final process called tempering. At 50 degrees Celsius liquid chocolate has the viscosity of 60 pa s, and at 30 degrees Celsius the viscosity is 100 pa s.

Cocoa butter has an unstable crystal structure, so it is heated and cooled to make a stable structure, this is known as tempering.

The chocolate is melted at about 46°c , the chocolate is then cooled to between 29°c and 31°c, and warmed up again to between 30°c and 32°c , it can then be held ‘in temper’ at this temperature for use as required. The chocolate is ready to be used for whatever it is needed for.


The table shows that the more cocoa and fat percentage the chocolate has, the higher the viscosity.

Social/environmental/historical context.

In the Cote D’Ivoire (Ivory Coast), young boys whose ages range from 12 to 16 have been sold into slave labour and are forced to work in cocoa farms in order to harvest the beans, from which chocolate is made, under inhumane conditions and extreme abuse.

English colonists carried chocolate (and coffee) with them to England’s colonies in North America, Which became the United States of America and Canada. They are now the world’s largest consumers of both Chocolate and Coffee, consuming over half of the words total production of chocolate alone.

Producing smooth chocolate affects the environment. Maintaining the temperature causes global warming by emitting greenhouse gases. Also, lowering or increasing the temperature, increases the cost compared to the cost of maintaining the temperature, so the production of chocolate would cost more than it should.

The benefit (for the manufacturer) of making chocolate less viscous is that less chocolate itself can be used to cover biscuits, sweets etc. although, to make chocolate less viscous, a higher temperature would be needed, which could result in higher energy costs.

Chocolate and Physics – Alfie Mussett

In order to discover more about the physics principles used in chocolate making, I took a trip to the Chocolate Unwrapped exhibition in London to talk to experts on the matter and gain new insight on the topic.

I went to the exhibition hall and spoke with people attempting to sell various different kinds of chocolate. I was unfortunately unable to extract much information from the people there because they were the trained to sell the chocolate and couldn’t tell me how it was made or the related principles and methods involved in the process. This information I found from research.

The first stage in the production of chocolate is fermenting the beans by means of a seven-day "microbial fermentation" of the pulp surrounding the cocoa bean. High temperatures of 50°C and various microbial products including acids kill the beans and result in the production of flavour precursors. However, over-fermentation results in fungi growing causing an off-tasting flavour. Next, the beans are washed and then dried until they become immune to microbial decay. They are then packed in sacks and shipped to countries such as the UK.

The beans are then gently roasted until they are tried and their full flavour is brought out. Roasting requires precision so that the product is of the highest quality. At this point, the bean still has a shell which will need to be removed. This is done via a process called "winnowing". This process entails transferring the beans to a winnower which removes the shells and leaves only the cocoa solids and cocoa butter. The beans are then cracked open and vibrated over a series of screens with progressively smaller openings; this makes sure that the larger pieces of the shell are removed while the cocoa solids and butter are collected for the next step in the process.

The penultimate step of the process is called "conching" where the chocolate is kneaded for anywhere between 1 to 3 whole days at 110 degrees celsius. The speed and temperature of the conching determines the final product’s texture and flavour as conching smooths the chocolate and mellows existing acidic tones. At this point, a problem may be encountered wherein the chocolate runs too slowly through the pipes and actually starts clogging the pipes up since the viscosity is so high due to high sugar content, a chocolate company could compensate for this problem by setting their machines to run at a higher temperature, resulting in the fluid having a lower viscosity and travelling through the pipes easier.

The final step of the process is called "tempering" and is vital to achieving the smooth, glossy look that store-bought chocolates have. Cocoa butter, which is one of the dominant ingredients in chocolate, has several triglycerides that lock into a crystal form when cooled and chocolate companies want to get the form that’s both the most practical and the most visually appealing, so they use tempering. Tempering involves carefully controlling the temperature of the chocolate as it cools, so that the chocolate favours the preferred state. This results in a chocolate, which looks glossy, is solid at room temperature and has a nice crisp snap when bitten into.

Chocolate report by Matthew Kelly

In this report I will be identifying the physics principles involved with the manufacture of chocolate. Throughout the report I will be referencing a visit that our class went on to the London Film Festival where ‘Chocolate Unwrapped’ was taking place. This is where I consulted experts on chocolate but not necessarily physics. So with their knowledge and further research into the application of physics I was able to find out about the physics of the manufacture of chocolate.

The ‘Chocolate Unwrapped’ exhibition took place on the 13th and 14th of October 2012. This two day chocolate show featured the top chocolatiers and chocolate companies from around the world. The venue consisted of stalls representing major companies such as Lindt and several other more individual manufactures and companies. I asked questions and took notes from several stalls.

During the visit I asked questions of several companies including ‘Rococo’, ‘C-Amaro’ referring to the manufacture of the chocolate and the properties that are to be considered when making chocolate and I received several answers and explanations.

The Physics involved in Chocolate making

Chocolate making is based on physics. The changing of these physics factors can affect the cost, time and profit. From the flow of chocolate during the production to the cross-sectional area of the chocolate is all based on physics. Viscosity is the frictional force in fluids. Viscosity is affected by the temperature of the fluid. When the chocolate is liquid its viscosity will decrease if you increase the temperature. In the production of chocolate the temperature must be average, so that it flows quickly while producing, but must be viscous enough to be shaped appropriately. Also the cross sectional area affects the stress required to break it and this will in turn affect the texture. When a liquid is able to move quicker it is less viscous. Also, when the cross sectional area is greater, the force required will also be great to break the chocolate piece.

To make the chocolate smooth and less viscous the temperatures must be raised and the dangerous hot liquids can result in injury. With technological advancements we can now measure the viscosity of the fluid but since chocolate is not transparent and is very dark it makes it much more difficult to measure the viscosity. One method that does work however is to use a tube of known length and heat the chocolate and measure the time it takes for the liquid chocolate to drain out of the tube. The time of flow and the temperature of the chocolate should be recorded.

Another method involves using a ball bearing with known radius attached to a gauge displaying distance. The ball bearing should be dropped and the terminal velocity should be recorded by using the time taken and the distance travelled by the ball bearing. This then can be used within Stoke’s Law and rearranged to give viscosity

h = (2g/9) x (r – s) x (a^2/v)

where r is the density of the ball bearing, a is the radius of the ball bearing, g is acceleration dues to gravity, v is the terminal velocity and s is the density of the fluid.

Environmental Context

Chocolate manufacture affects the environmental. Maintaining the high temperatures can increase the emission of greenhouse gases causing global warming. Lowering or increasing the temperature can result in a larger than maintaining the temperature. Making the final price of product manufacture costs higher and in turn making the retail price higher which may deter people from buying the chocolate.

Historical Context

Dutchman Casparus Van Houten patented hydraulic cocoa press in 1828. Cocoa for drinking contained over 50% fat, and it was difficult to digest. Van Houten could separate cocoa butter from cocoa liquor with his press and produce low-fat cocoa powder. Thanks to this invention it was possible to make chocolate bars we know today. First chocolate bars were probably produced by English company Fry´s from Bristol in 1847. Swiss Rodolphe Lindt invented the conching process in 1879. Thus one could produce fine chocolate, which melts on the tongue.

Viscosity experiments

In a physics lesson I carried out several practicals that can be used to investigate the viscosity of liquids. I used a version of the Redwood Viscometer, consisting of a funnel attached to a tube. The funnel had two points 1cm apart marked on it and I timed how long it took for a liquid to flow through the funnel between the two marks. I used two different types of tube, a large bore for higher viscosity liquids and a small bore for low viscosity liquids. I used different substances such as syrup, two types of honey and different concentrations of sugar solution. In this experiment the higher the viscosity the longer it takes to drain through a tube and this can refer to transport speeds in chocolate manufacture.

Another experiment carried out was the time it takes for containers of different viscous liquids to roll 1m down a ramp. The liquids had different viscosities because they had been stored at different temperatures. Here are the results.


Picture from Edexcel AS Physics Book Page 59

Temperature of Syrup/oC       Time to roll down 1m/s

               -5                                                                    1.00

             22                                                                      1.22

             25                                                                      1.22

            35                                                                        1.48

           40                                                                         1.62

What the results show is that the higher the temperature the longer it takes the container to roll down the ramp. This might be surprising as you would expect a lower viscosity to flow more rapidly but this is exactly why the results are as they are. The gravitational potential energy given to the container as it is lifted to the raised end of the ramp is transferred to kinetic energy of the container and the liquid inside as the container rolls down the ramp. The lower the viscosity of the liquid the greater the amount of kinetic energy it takes to move in the container leaving less kinetic energy for the container so the container takes longer to move. Therefore it is not surprising that the frozen liquid container rolls the fastest as the liquid is not free to move much.

Chocolate Report by Wing Chung Hau

For my AS course, I visited a chocolate convention – ‘Chocolate Unwrapped’ which took place on the 13th and 14th of October in Covent Garden, London to learn about the properties of chocolate and how it changes with pressure/force and temperature by asking the experts at the convention.

In order for the chocolate to be used properly chocolate makers need to know its melting point, water activity and viscosity.

The viscosity of chocolate is dependent on many different factors; the fat and sugar content, emulsifiers, moisture, particle size, temperature and state of temper.

The melting point of chocolate affects its outcome as it determines the texture of the chocolate and is based on how much fat the chocolate contains. Water activity is important as when the amount of water in the chocolate increases its viscosity also increases and this has many different effects. Viscosity is the drag or frictional force in fluids and where there is a high amount of viscous drag the liquid chocolate flows slower and is harder to transport as it can block up machines and requires quite a bit of energy. Viscosity is extremely important to the making of chocolate; it helps manufacturers financially as it reduces wastage due to too much chocolate being used because of a slower flow rate due to high viscosity.


Table from Edexcel AS Physics Book Page 59

At lower temperatures, chocolate has a higher viscosity, when the temperature increases, viscosity decreases due to it being less dense and thinner. The chocolate needs to have the lowest viscosity possible for its machines to operate as this reduces costs and makes manufacturing easier; there will be less wastage, easier for machines to process and transport the chocolate as chocolate with high viscosity will not flow well making the process slower and increasing the chance of damaging machines by clogging them up.

The social impacts of chocolate manufacturing are that the public get to enjoy a good quality chocolate with a decent quality. If manufacturers abuse low viscosities they can save money as they reduce the content of chocolate per sweet. This could make the chocolate degraded in quality compared to manufacturers who do not use the lowest possible viscosities for cost reasons, manufacturers can also change viscosity to change the chocolate and bring out a different product for consumers.

The environmental impacts of chocolate manufacturing are less wastage of chocolate because of lower viscosities which is good for the planet, however to produce a lower viscosity for chocolate, you need higher temperatures which are generated by a power station which normally uses fossil fuels, this negatively impacts the environment as it produces greenhouse gasses which damage the planet.

Chocolate was re-discovered by the Spanish. They ground certain ingredients with dried cocoa beans such as sugar, heated the mixture to make a paste and placed it on leaves, letting it harden. They didn’t utilise viscosity.

The benefit of lower viscosity is that the frictional force is lower and this lowers the energy required to move or process the fluid as the opposing force is weaker. The flow rate is directly related to the viscosity. With higher viscosities the frictional force is bigger which makes it difficult for the fluid to flow, lowering the flow rate. With a lower viscosity, the frictional force is smaller which makes it easier for the fluid to flow which increases flow rate which increases productivity for making chocolate, which results in higher profits.

The risk associated with a high viscosity is a reduction in the flow rate of chocolate and when this happens it could clog up and damage the machine processing the chocolate.

We carried out a practical using a Redwood viscometer to see how the viscosity of different sugar solutions affected the flow rate. When there was a higher concentration of sugar the viscometer found it hard to pass the solutions, therefore the more sugar in the water, the higher the viscosity. This relates to chocolate as most chocolates contain sugar and this will affect its viscosity, the greater the quantity of sugar the greater the viscosity of the liquid chocolate.

The picture below is a proper redwood viscometer that would be used in the chocolate industry. The idea is to time how quickly a set volume of liquid is collected in a container after passing through a tube. The temperature of the liquid can be changed by the apparatus.


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