The Engineering and Chemistry Behind Sugar
Key words: sugar refining, chemical engineering, biochemistry, organic sugar, high fructose
corn syrup
The history of sugarcane cultivation has at least been 10,000 years. Although sugar was
discovered since the start of human civilization, technologies that could massively
extract crystalized sugar were not invented until the 16th century. Sugar was such
valuable merchandise at the time that its price was comparable to that of sterling, ivory
and pearl. Today, Americans consume more than 10 teaspoon of cane sugar and 8
teaspoon of high fructose corn syrup on a daily basis. The technologies behind sugar
making have advanced and the products diversified. Consumers today face a
bewildering variety of sugar products, as well as the danger of excess sugar intake.
Introduction
“It’s a prime ingredient in countless substances from cereal to soup, from cola to coffee.
Consumed at the rate of one hundred pounds for every American every year, it’s as
addictive as nicotine — and as poisonous.
It’s sugar.” —“The Sugar Blues” by William Dufty [1].
It is surprising how sugar has changed the world. Sugar has been the most important
trading commodity since the 16th century. “White gold”, as British colonists called it, was the
biggest incentive for slave trade that forever shaped the Southern United States. Even today,
the sugar and candy industries are still among the most profitable businesses in the United
States. Caramels, chocolates, gummies, lollypop… Sugar products are everywhere, not to
mention sugar is a prime ingredient in almost every food we eat!
The variety of sugar products we see today is a result of the industrial successes of
sugar production during the 20th century. Technological advances in sugarcane agriculture
and sugar refining have greatly promoted the production of cane sugar, and have made it
possible to produce sugar from cornstarch. High fructose corn syrup was invented in the
1950s, which partially replaced cane sugar as a beverage sweetener. What follows are
boom of the candy and beverage industries, and almost simultaneously a dramatic increase
in obesity and diabetes rates.
The modern American culture encourages people to enjoy sweets. Candies are a big
part of Easter, Christmas and Halloween. The modern American culture can be described as
Ke 2
a “candy culture”, or perhaps more precisely a sugar culture. Besides providing the delicious
candy products, the candy industry provides millions of jobs, and contributes to billions of
dollars of value every year in the modern American economy.
But the American fascination of candy is certainly not without consequence.
Americans consume the most sugar in the world, on average 130 to 140 pounds per year
since 2001 [2]. Sugar, only second to trans fat, is to blame for the obesity epidemic. Sugar
consumption is also positively correlated with diabetes, hypertension and heart disease.
Besides table sugar, sweeteners such as High Fructose Corn Syrup are also causes of
health issues. So what role does engineering play in this situation? Why is sugar so bad for
your body?
Sugar History and Product Variety
Sugar is the biological fuel used by all living things. In living cells, sugar is usually
made into starch and glycogen for storage. Only a few plant species are naturally abundant
in sugar, most of which are valuable sugar crops. The earliest evidence of cane sugar
cultivation dated back to some 10,000 years ago in New Guinea. Sugarcane was introduced
by Christopher Columbus to the New World in 1493. By the middle of the 16th century, there
were already thousands of sugar mills in the Caribbean Sea’s precious sugar islands. Cane
sugar production had great impact on the economic lives of Americans, until corn syrup was
invented in the 20th century. Before that, sugar cane, beet, barley and maple trees were the
most common sources for sugar production.
The per capita consumption of sucrose (table sugar) has dropped from 60 grams per
year in 1970s to around 40 grams in 2011 [2], because of the invention of high fructose corn
syrup. Still, sucrose is Americans’ most common choice for cooking and beverages. In
groceries, all of the solid form sugar products are sucrose. Cane sugar makes up most of
the table sugar production in the world, while beet sugar occupies the remainder. Though
table sugar is all extracted from plants, the actual products vary tremendously in color, form,
density and flavor. Cane sugar, for example, could be divided into white sugar, light brown
sugar and black sugar by color. Black sugar is usually cheaper and more flavorful, although
less pure. Refined cane sugar could also be divided into rock sugar, granulated sugar and
caster (fine powdered) sugar by the size of the crystal. White rock sugar and castor sugar
are produced from recrystallization of granulated sugar, so they are purer and more
expensive. In the United States, caster sugar is sold as “superfine” sugar.
Ke 3
granulated sugar (left) and
Rock sugar
castor sugar (right)
Figure 1: Classification of Cane Sugar by Color and Crystal Size
white, golden to brown sugar
Syrup products, such as honey and maple syrup, are blends of approximately 1:1
ratio of glucose and fructose with about 10% water; there are also a little sucrose, maltose,
larger saccharides and trace amount of other chemicals. Their compositions are much more
complex than table sugar. The exact compositions of honey and maple syrup are
undetermined, but they are known for consisting of trace amounts of minerals, vitamins,
enzymes, etc. Honey and fruit syrups are believed to have superior health benefits
compared to table sugar.
Chemistry of Sugar
In biochemistry, the word “sugar” has the same meaning as “saccharide”, which
comes from the Greek word “σάκχαρον”. Sugars are all carbohydrates, and could be written
with the empirical formula Cm(H2O)n. In Greek, “mono-” and “di-” means “single-” and “two-”.
If the carbohydrate molecule only contains one ring, it is called “monosaccharide”; if the
molecule is made of two connected rings, it is called “disaccharide”. Monosaccharides and
disaccharides are commonly referred to as “sugar” because most of them have a sweetflavor.
Figure 2: Monosaccharides: Glucose, Fructose and Galactose
Ke 4
Figure 3: Disaccharides: Maltose, Sucrose and Lactose
Simple sugars have numerous isomers, but only a few are sweet and commonly
used as food. When we say the word “sugar” in food science or in informal contexts, we are
only referring to a few compounds that could provide energy for the living cell. Among the
most important sugar molecules, glucose, fructose and galactose are monosaccharides,
while sucrose, lactose, and maltose are disaccharides.
How Is Table Sugar Made? The Sugar Refining Process
All sugars are natural; the refineries simply extract them from plants to grow and
harvest sugar crystals. The chemical and process engineering in sugar refining has changed
drastically since the time it was invented, but the underlining principles are still the same.
Different forms of sugars vary in their purity and utility, and are sold at different prices in the
market. Purity is largely determined by choices in the manufacturing process. The sugar
refining processes are discussed in many books and publications, an excellent example of
which would be the “Handbook of Sugar Refining” [3].
Sugar refining is a very complicated process that consists of more than ten steps
[3][4][5]. The most important processes are summarized in Figure 4. Sugar cane first needs
to be washed and mechanically crushed. Through crushing, the juice is completely extracted
from the sugar cane. The juice is then filtrated and fed to a boiler, where about ¾ of the
liquid by volume is evaporated. The evaporation process will yield a dense and viscous
brown liquid called molasses. The molasses is then fed to a crystallizer, where the sugar
crystals grow as the liquid cools down. The solid crystals are then centrifuged and then dried
by blowing hot air. A brown or black product called “raw sugar” is usually generated from this
first crystallization. Raw sugar is a very coarse product. It cannot be sold at the market
because it contains impurities such as dirt. Usually it is dissolved again in a stirred tank to be
further processed. Purer products are made by further refining raw sugar through
recrystallization [3].
Ke 5
Sugarcane
Molasses
Crusher
Evaporator
Crystallizer
Clarifier
Blender
Centrifuge
Filter
Raw Sugar
Shipment
Ion Exchange Column
Crystallizer
Centrifuge
Drier
Figure 4: A Simplified Industrial Sugar Refining Process Made with Microsoft Visio
To enhance sugar recovery and remove undesirable colors, certain chemicals are
applied in a process called clarification. Conventionally, sugar juice clarification is achieved
through drum filter using activated carbon filters and ion exchangers without adding any
chemicals. But industrially, the process of adding clarifying agent to form precipitation, which
is called flocculation, is more cost-effective. Chemical flocculation uses sulphitation,
carbonation or phosphatation mechanisms. Hydrated lime juice containing calcium
hydroxide (Ca(OH)2) is added, which forms insoluble precipitation with sulfur dioxide, carbon
dioxide or phosphoric acid. The precipitation acts as a flocculent that absorbs most color and
impurities. After crystallization, all of the chemicals will remain in the juice while white
granular sugar crystals are harvested.
White cane sugar is usually the most popular product. If the clarification process is
thorough, the product after the first recrystallization would be granulated white sugar. If the
clarification process only removes dirt and insoluble impurities, the recrystallization product
would be black or brown sugar, sometimes called “sugar in raw”. It is a delicious, flavorful
and nutritious product that could be directly used for human consumption. Sugar cane is
always a better choice for black sugar production than beet. Beet sugar is produced in a
similar process, but requires an extra initial step using boiling water for extraction. Beet
sugar molasses also has a bitter taste so it is not as desirable.
More recrystallization steps need to be carried out to yield purer products such as
white rock sugar and castor sugar [4][5]. There are also unconventional products such as
light/golden brown sugar, which are made by recrystallizing granulated white sugar with a
little molasses added back. In this way, the sugar crystals grow larger that have a more
pleasant color. Because the molasses added are so little, this type of golden brown sugar is
Ke 6
essentially the same as white sugar. It is quite different from the “raw cane sugar” or “sugar
in raw” that is sold in groceries, although they might have similar color.
Corn Syrup? The Corn and Sugar Economy
Sugar is very desirable merchandise. However, the cultivation of sugar cane requires
a lot of heat and water. In the US, sugar cane is only commercially grown in Florida, Hawaii,
Louisiana, South Carolina and Texas. Table sugar is also relatively expensive because of
the high cost in sugarcane cultivation and sugar refining.
One merit of engineering is the ability to find alternative solutions to existing
problems. The US economy produces an excess of cheap corn. During the 20th century, the
industry found it tremendously profitable to hydrolyze corn starch to produce sugars. Starch
is a large macromolecule that is made by interconnecting roughly 200-3000 glucose
molecules. Cornstarch will be first mixed with dilute acid, and then treated with two enzymes:
alpha-amylase and glucoamylase [6]. The resulting product is a clear liquid called corn
syrup. Depending on the degree of hydrolysis, corn starch could yield maltose (disaccharide)
or glucose (monosaccharide). The former is called high maltose corn syrup, but the latter is
a more desirable product because glucose is sweeter. The term “corn syrup” generally refers
to the latter product that is roughly 90% glucose and 10% water.
Corn syrup is just as healthy as table sugar. It is actually superior in a lot of ways
such as its low freezing point, low viscosity, light color and the ability to soften candy texture.
Most importantly, it is cheap. About 950g of starch could produce 1kg of syrup. The common
sweetener that is used in soft drinks, however, is actually a quite different product called
high fructose corn syrup (HFCS).
HFCS has either 42% or 55% of fructose, a quite similar sugar distribution as honey
[6][7]. Fructose is a much sweeter isomer of glucose that is commonly found in fruits. HFCS
is more desirable because it gives a natural taste to fruit-flavored drinks (Sprite, Dr. Pepper,
Fanta, etc.). HFCS is made by further processing corn syrup through a packed bed reactor
with an enzyme called D-xylose isomerase, where about half of the glucose will be
converted to yield a mixture of 42-44% fructose product [6]. A higher 55% fructose product
could be made through liquid chromatography processing [6].
How bad is HFCS? Bioenergetics and Sugar Metabolism
Ke 7
Sugars are more likely to cause obesity than any other carbohydrates.
Macromolecules such as starch and animal fat require a lot of digestion, and thus are slow
for the body to absorb. On the contrary, saccharides are small molecules that are easily
dissolved in water, which makes them fast to be absorbed into the bloodstream. High
fructose consumption is particularly unhealthy because it is metabolized through a different
pathway than glucose. Although fructose has exactly the same number of calories as
glucose, its consumption more strongly relates to obesity, type II diabetes and
cardiovascular problems.
One commonly accepted argument is that fructose causes problems by bypassing
the rate-limiting step of glycolysis [8]. Glycolysis is the metabolic pathway converting sugar
to pyruvate, the first step of converting sugar to carbon dioxide or fat. When there is excess
energy supply in the body, carbohydrates will be either stored as glycogen while the rate of
glycolysis is limited. All carbohydrates must be first converted to fructose or glucose before
entering glycolysis [8]. Glucose is first converted to fructose 6-phosphate; it is then
converted to fructose 1, 6-biphosphosphate by the enzyme phosphofructokinase (PFK). The
PFK reaction is the rate-limiting step of glycolysis. When there is an excess of glucose, the
production of fructose 1,6-biphosphosphate is suppressed. Fructose, however, is primarily
metabolized in the liver, where it is first phosphorylated to fructose 1-phophate. By
phosphorylating the 1-position, it bypasses the rate-limiting reaction of PFK. When there is
excess fructose intake, the body quickly converts fructose to fructose 1-phophate and then
fructose 1,6-biphosphosphate, shifting the balance of glycolysis’s downstream reactions [8].
The result favors the biogenesis of low LDL (low density lipoprotein, the “bad cholesterol”)
and triglycerides (blood fat).
Organic Sugar? “Healthier” Sugars and Sugar Substitutes
Sucrose, or white table sugar is void of any vitamins, fibers, amino acids or other
trace nutrition that are normally found in sugar cane. All refined white sugars are formally
referred to as “empty calories”, because they add calories to the diet without adding any
nutrition value. There are many alternative sweeteners to refined sugar and HFCS, such as
“raw cane sugar”, plant syrup, molasses and honey. In comparison, black or brown “raw”
cane sugar is not only cheaper: because it does not go through complete clarification, it is
less pure, having less calories and more nutrition. It is not less healthy because of the
impurities: the FDA has strict policy against human consumption of raw sugar containing
impurities that make it unhealthy for human consumption [9]. All “raw cane sugar” and “sugar
in raw” products in the groceries are essentially brown sugar.
Ke 8
“Organic cane sugar” is thought to be a better product, although it is still considered
as empty calories. Various standards exist whether the sugar could be labeled as “organic”.
“Organic” applies to a product that is produced from organic farming. It means that no
pesticides could be used in the growing methods. Because sugarcane cultivation generally
requires a lot of pesticides, growing in organic methods incurs crop loss that makes the
production considerably more expensive. Chemicals are not allowed in the refining process
either, meaning that only activated carbon can be used for clarification. It is still controversial
whether these stringent requirements make any difference for refined sugar. Most organic
sugars are lightly processed brown sugars. There are fine white sugars that are produced
from organic sugarcane or beet, but less common.
The prominent health hazard of all sugar consumption is tooth decay. Oral bacteria
quickly converts sugar to lactate, an acid that could gradually break down tooth’s minerals.
Overconsumption of sugars also tends to rapidly increase blood glucose. Aside from weight
gain, it could contribute to hypertension, cardiovascular problems and Type II diabetes [10].
Fructose is a notorious alternative to glucose for reasons discussed in the previous section.
Sucrose could also be easily broken down to glucose and fructose in the human body. So
for a healthy diet, it is highly recommended to limit both sucrose and HFCS consumption.
One of the ways to reduce calories intake from sugar is to use synthesized sugar
substitutes. Most of them are engineered through organic synthesis. These sugar substitutes
are zero calorie carbohydrates that are at least 100 times sweeter than sugars. They are
used for purposes such as weight loss, dental care and blood sugar control. They are not
helpful in the case of sugar addiction, however. Also, it is less understood how sugar
substitutes could affect metabolism and signaling pathways. Controversial evidence exists
that some sugar substitutes actually cause increased appetite and metabolic syndrome.
Conclusion
The discovery of sugar as consumer goods has dramatically affected people’s lives.
What came along with the invention of sugar refining was great prosperity. The principles
underlining the refining practices have not changed a lot since it was invented. But due to
the improvements in engineering practices, what was luxury in the past is now available at
very cheap prices. These changes in engineering also have dramatic impacts on people’s
lives. The growing consumption of sweetener products, most representative high fructose
corn syrup, has greatly affected the way people understand sugars. There is no doubt that
the sugar industry will continue to grow and the technologies will keep improving.
Ke 9
Reference
[1] W. Dufty. “Sugar Blues”. New York: Warner Books Printing, 1976, pp. 258.
[2] United States Department of Agriculture. Sugar and Sweeteners Yearbook Tables.
U.S. Consumption of Caloric Sweeteners. (2012, Sep. 12). Table 49-53 [Online].
Available: http://www.ers.usda.gov/data-products/sugar-and-sweeteners-yearbooktables.aspx#25512
[3] Canadian Sugar Institute. The Journey of Sugar. Available:
http://www.sugar.ca/english/educators/thejourneyofsugar.cfm
[4] Southern Minnesota Beet Sugar Cooperative. Available:
http://www.smbsc.com/SugarProcess/Intro.aspx
[5] C. C. Chou. “Handbook of Sugar Refining: A Manual for the Design and Operation of
Sugar Refining Facilities”. New York: John Wiley & Sons, Inc. Jan 15 2000.
[6] N. S. Mosier, M. R. Ladisch. “Modern Biotechnology: Connecting Innovations in
Microbiology and Biochemistry to Engineering Fundamentals”. Hoboken: John Wiley
& Sons, Inc., 2009, pp. 51-56.
[7] D. W.Ball. “The Chemical Composition of Honey”. Journal of Chemical Education.
Vol. 84, No. 10, Oct 2007.
[8] J. M. Berg et al. “Biochemistry”. W. H. Freeman & Co, 2007. Ch. 15-18.
[9] U.S. Food and Drug Administration. Inspections, Compliance, Enforcement, and
Criminal Investigations. CPG Sec. 515.400 Raw Sugar [Online]. (Issued 1980, Oct. 1,
Revised Mar. 1995). Available:
http://www.fda.gov/ICECI/ComplianceManuals/CompliancePolicyGuidanceManual/u
cm074439.htm
[10] R. Nalini. “Health Risks of Sugar-Sweetened Beverage Consumption”. Pediatrics for
Parents 27, 3/4, pp. 2-3. Mar.-Apr. 2011.