# Ketchup

Type A dish of tomato ketchup Condiment Tomatoes (or other main ingredients), Sugar (or high fructose corn syrup), vinegar, salt, spices, and seasonings 103 kcal (431 kJ)

Ketchup is a table sauce. Although original recipes used egg whites, mushrooms, oysters, grapes, mussels, or walnuts, among other ingredients,[1][2] the unmodified modern recipe refers to tomato ketchup in the USA.[3]

Tomato ketchup is a sweet and tangy sauce made from tomatoes, sugar, and vinegar, with seasonings and spices. The spices and flavors vary, but commonly include onions, allspice, coriander, cloves, cumin, garlic, and mustard, and sometimes include celery, cinnamon, or ginger.[4]

The market leader in the United States (60% market share) and United Kingdom (82%) is Heinz Tomato Ketchup.[5][6] In some of the UK, South Africa and Australia, ketchup is also known as "tomato sauce" (a term that means a fresher pasta sauce elsewhere) or "red sauce" (especially in Wales).

Tomato ketchup is most often used as a condiment to dishes that are usually served hot and may be fried or greasy: french fries, hamburgers, hot dogs, chicken tenders, tater tots, hot sandwiches, meat pies, cooked eggs, and grilled or fried meat. Ketchup is sometimes used as the basis for, or as one ingredient in, other sauces and dressings, and the flavor may be replicated as an additive flavoring for snacks, such as potato chips.

## History

### Etymology

In the 17th century, the Chinese mixed pickled fish and spices and called it (in the Amoy dialect) kôe-chiap or kê-chiap (鮭汁, Mandarin Chinese guī zhī, Cantonese gwai1 zap1) meaning the brine of pickled fish (鮭, salmon; 汁, juice) or shellfish.[7][8] By the early 18th century, the table sauce had arrived in the Malay states (present day Malaysia and Singapore), where English colonists first tasted it. The Malaysian-Malay word for the sauce was kicap or kecap (pronounced [kɛt͡ʃap]). That word evolved into the English word "ketchup".[9]

The term Catchup was used in 1690 in the Dictionary of the Canting Crew[10] The spelling "catchup" may have also been used in the past.[11]

### Mushroom ketchup

Homemade mushroom ketchup in a plastic tub

In the United Kingdom, preparations of ketchup were historically and originally prepared with mushrooms as a primary ingredient, rather than tomatoes.[12][13][14] Ketchup recipes began to appear in British and then American cookbooks in the 18th century. In a 1742 London cookbook, the fish sauce had already taken on a very British flavor, with the addition of shallots and mushrooms. The mushrooms soon became the main ingredient and from 1750 to 1850 the word "ketchup" began to mean any number of thin dark sauces made of mushrooms or even walnuts.[15] In the United States, mushroom ketchup dates back to at least 1770, and was prepared by British colonists in the Thirteen Colonies.[16] In contemporary times, mushroom ketchup is available in the UK, although it is not a commonly used condiment.[17]

### Tomato ketchup

Tomato ketchup and other condiments
Tomato ketchup next to raw tomatoes

Many variations of ketchup were created, but the tomato-based version did not appear until about a century after other types. An early recipe for "Tomata Catsup" from 1817 still has the anchovies that betray its fish-sauce ancestry:[15]

1. Gather a gallon of fine, red, and full ripe tomatas; mash them with one pound of salt.
2. Let them rest for three days, press off the juice, and to each quart add a quarter of a pound of anchovies, two ounces of shallots, and an ounce of ground black pepper.
3. Boil up together for half an hour, strain through a sieve, and put to it the following spices; a quarter of an ounce of mace, the same of allspice and ginger, half an ounce of nutmeg, a drachm of coriander seed, and half a drachm of cochineal.
4. Pound all together; let them simmer gently for twenty minutes, and strain through a bag: when cold, bottle it, adding to each bottle a wineglass of brandy. It will keep for seven years.

By the mid-1850s, the anchovies had been dropped.[15]

James Mease published another recipe in 1812. In 1824, a ketchup recipe using tomatoes appeared in The Virginia Housewife (an influential 19th-century cookbook written by Mary Randolph, Thomas Jefferson's cousin). American cooks also began to sweeten ketchup in the 19th century.[18]

As the century progressed, tomato ketchup began its ascent in popularity in the United States. Ketchup was popular long before fresh tomatoes were.[19] People were less hesitant to eat tomatoes as part of a highly processed product that had been cooked and infused with vinegar and spices.[19]

Tomato ketchup was sold locally by farmers. Jonas Yerkes is credited as the first American to sell tomato ketchup in a bottle.[20] By 1837, he had produced and distributed the condiment nationally.[21] Shortly thereafter, other companies followed suit. F. & J. Heinz launched their tomato ketchup in 1876.[22] Heinz Tomato Ketchup was advertised: "Blessed relief for Mother and the other women in the household!", a slogan which alluded to the lengthy process required to produce tomato ketchup in the home.[23] With industrial ketchup production and a need for better preservation there was a great increase of sugar in ketchup, leading to our modern sweet and sour formula.[15] In Australia, it wasn't until the late 19th century that sugar was added to tomato sauce, initially in small quantities, but today contains just as much as American ketchup and only differed in the proportions of tomatoes, salt and vinegar in early recipes.[24]

The Webster's Dictionary of 1913 defined "catchup" as: "table sauce made from mushrooms, tomatoes, walnuts, etc. [Also written as ketchup]."

Modern ketchup emerged in the early years of the 20th century, out of a debate over the use of sodium benzoate as a preservative in condiments. Harvey W. Wiley, the "father" of the Food and Drug Administration in the US, challenged the safety of benzoate which was banned in the 1906 Pure Food and Drug Act. In response, entrepreneurs including Henry J. Heinz, pursued an alternative recipe that eliminated the need for that preservative.[4] Katherine Bitting, a microbotanist working for the U.S. Department of Agriculture, carried out research that proved in 1909 that increasing the sugar and vinegar content of the product would prevent spoilage without use of artificial preservatives. She was assisted by her husband, Arvil Bitting, an official at that agency.[25]

Prior to Heinz (and his fellow innovators), commercial tomato ketchups of that time were watery and thin, in part due to the use of unripe tomatoes, which were low in pectin.[26] They had less vinegar than modern ketchups; by pickling ripe tomatoes, the need for benzoate was eliminated without spoilage or degradation in flavor. But the changes driven by the desire to eliminate benzoate also produced changes[clarification needed] that some experts (such as Andrew F. Smith[27]) believe were key to the establishment of tomato ketchup as the dominant American condiment.

### Later innovations

In fast-food outlets, ketchup is often dispensed in small sachets or tubs. Diners tear the side or top and squeeze the ketchup out of the ketchup packets, or peel the foil lid off the tub for dipping. In 2011, Heinz began offering a new measured-portion package, called the "Dip and Squeeze" packet, which can be opened in either way, giving both options.[28]

Some fast food outlets previously dispensed ketchup from hand-operated pumps into paper cups. This method has made a comeback in the first decade of the 21st century, as cost and environmental concerns over the increasing use of individual plastic ketchup tubs were taken into account. In-N-Out Burger is an example of a restaurant offering this type of dispensing.

In October 2000, Heinz introduced colored ketchup products called EZ Squirt, which eventually included green (2000), purple (2001), mystery (pink, orange, or teal, 2002), and blue (2003).[29] These products were made by adding food coloring to the traditional ketchup. As of January 2006 these products were discontinued.[30]

In March of 2018 a kickstarter campaign was launched for sliced ketchup.[31] Reception has been polarized, where Time news cited reviews negatively declaring it "a crime", and positively as "revolutionizing the way we sauce".[32]

## Terminology

The term used for the sauce varies. Ketchup is the dominant term in American English and Canadian English, although catsup is commonly used in some southern US states and Mexico.[33]

Tomato sauce is more common in English-speaking countries outside North America.[34] In Canada and the US tomato sauce is not a synonym for ketchup but a sauce made from tomatoes and commonly eaten with pasta.

Red sauce is the term used in Welsh English, Scottish English and some parts of England, such as the Black Country, and in South London, contrasting with brown sauce. In Canadian and American English, "red sauce" refers to various tomato-based sauces commonly paired with pasta dishes, and is not a synonym for ketchup.[citation needed]

## Etymology

The etymology of the word ketchup is unclear, with multiple competing theories:[35]

### Chinese theory

One theory is that the word came to English from the Cantonese "keh jap" (茄汁 ke2 zap1, the word literally means "tomato sauce" in Cantonese).[36] An alternative theory is that the word derives from one of two words from Hokkien of the Fujian region of coastal southern China: "kôe-chiap" (in Xiamen and Quanzhou) or "kê-chiap"[8][37] (in Zhangzhou and Guangzhou). Both of these words (鮭汁, kôe-chiap and kêchiap) come from either the Quanzhou dialect, Amoy dialect, or Zhangzhou dialect of Hokkien, where it meant the brine of pickled fish (鮭, salmon; 汁, juice) or shellfish.[7] There are citations of "koe-chiap" in the Dictionary of the Vernacular or Spoken Language of the Amoy (London; Trudner) from 1873, defined as "brine of pickled fish or shell-fish".

### Malay theory

Ketchup may have[9] entered the English language from the Malay word kicap (pron. "kichap", sometimes spelled kecap or ketjap). Originally meaning "fish sauce", the word itself derives from the Chinese terms[38] above.

In Indonesian cuisine, which is similar to Malay, the term kecap refers to fermented savory sauces. Two main types are well known in their cuisine: kecap asin which translates to 'salty kecap' in Indonesian (a salty soy sauce) and kecap manis or "sweet kecap" in Indonesian. Kecap manis is a sweet soy sauce that is a mixture of soy sauce with brown sugar, molasses, garlic, ginger, anise, coriander and a bay leaf reduced over medium heat until rather syrupy. A third type, kecap ikan, meaning "fish kecap" is fish sauce similar to the Thai nam pla or the Philippine patis. It is not, however, soy-based.

### European-Arabic theory

American anthropologist E.N. Anderson relies on Elizabeth David to claim that ketchup is a cognate of the French escaveche, meaning "food in sauce".[39] The word also exists in Spanish and Portuguese forms as escabeche, "a sauce for pickling", which culinary historian Karen Hess traced back to Arabic Kabees, or "pickling with vinegar". The term was anglicized to caveach, a word first attested in the late 17th century, at the same time as ketchup.[35]

### Early uses in English

The word entered the English language in Britain during the late 17th century, appearing in print as catchup (1690) and later as ketchup (1711). The following is a list of early quotations collected by the Oxford English Dictionary.

The first published recipe: it included mushrooms, anchovies and horseradish.
• 1730, Jonathan Swift, A Panegyrick on the Dean Wks. 1755 IV. I. 142
• And, for our home-bred British cheer, Botargo, catsup, and caveer.
• 1748, Sarah Harrison, The Housekeeper's Pocket-Book and Compleat Family Cook. i. (ed. 4) 2,
• I therefore advise you to lay in a Store of Spices, ... neither ought you to be without ... Kitchup, or Mushroom Juice.
• 1751, Mrs. Hannah Glasse, Cookery Bk. 309
• It will taste like foreign Catchup.
• 1817, George Gordon Byron, Beppo viii,
• Buy in gross ... Ketchup, Soy, Chili~vinegar, and Harvey.
• 1832, Vegetable Substances Used for the Food of Man 333
• One ... application of mushrooms is ... converting them into the sauce called Catsup.
• 1840, Charles Dickens, Barnaby Rudge (1849) 91/1
• Some lamb chops (breaded, with plenty of ketchup).
• 1845, Eliza Acton, Modern Cookery v. (1850) 136 (L.)
• Walnut catsup.
• 1862, Macmillan's Magazine. Oct. 466
• He found in mothery catsup a number of yellowish globular bodies.
• 1874, Mordecai C. Cooke, Fungi; Their Nature, Influence and Uses 89
• One important use to which several ... fungi can be applied, is the manufacture of ketchup.

## Composition

Heinz tomato ketchup's ingredients are: tomato concentrate from red ripe tomatoes, distilled vinegar, high fructose corn syrup, corn syrup, salt, spice, onion powder, and natural flavoring.[41] Ingredients are listed from highest to lowest percentage weight.

### "Fancy" ketchup

Some ketchup in the U.S. is labeled "Fancy". This is a USDA grade, relating to specific gravity. Fancy ketchup has a higher tomato solid concentration than other USDA grades.[42]

Fancy 1.15 33%
Extra Standard 1.13 29%
Standard 1.11 25%

## Processing

After sorting, washing, and chopping, tomatoes are placed into large steel vats for preservation and precooking. Tomato juice and pulp are separated by filtering and screening. Once separated, the juice is further processed into ketchup. Ketchup processing includes adding additional ingredients, cooking, more screening and filtering, air-removal, packaging and cooling.

After juice filtration, additional ingredients are added to the mixture to achieve the desired taste and consistency. Throughout the entire process, the temperature must be constantly monitored to make sure all ingredients are properly mixed. Air is then removed to prevent oxidation, maintain proper coloring and inhibit the growth of any unwanted bacteria. Before being packaged, the ketchup is heated to approx.190 °F (88 °C) to prevent contamination. After packaging, the bottles are immediately sealed and cooled to preserve freshness and improve shelf-life of the product.

## Nutrition

The following table compares the nutritional value of ketchup with raw ripe tomatoes and salsa, based on information from the USDA Food Nutrient Database.[43]

Nutrient
(per 100 g)
Ketchup Low sodium
Ketchup
Tomatoes,
year-round
USDA commodity
salsa
Energy 100 kcal
419 kJ
104 kcal
435 kJ
18 kcal
75 kJ
36 kcal
150 kJ
Water 68.33 g 66.58 g 94.50 g 89.70 g
Protein 1.74 g 1.52 g 0.88 g 1.50 g
Fats 0.49 g 0.36 g 0.20 g 0.20 g
Carbohydrates 25.78 g 27.28 g 3.92 g 7.00 g
Sodium 1110 mg 20 mg 5 mg 430 mg
Vitamin C 15.1 mg 15.1 mg 12.7 mg 4 mg
Lycopene 17.0 mg 19.0 mg 2.6 mg n/a

## Viscosity

Transferring ketchup between plastic bottles

Commercial tomato ketchup has an additive, usually xanthan gum, which gives the condiment a pseudoplastic or "shear thinning" property - more commonly known as thixotropic.[citation needed] This increases the viscosity of the ketchup considerably with a relatively small amount added—usually 0.5%—which can make it difficult to pour from a container. However, the shear thinning property of the gum ensures that when a force is applied to the ketchup it will lower the viscosity enabling the sauce to flow. A common method to getting ketchup out of the bottle involves inverting the bottle and shaking it or hitting the bottom with the heel of the hand, which causes the ketchup to flow rapidly. A technique involves inverting the bottle and forcefully tapping its upper neck with two fingers (index and middle finger together). Specifically, with a Heinz ketchup glass bottle, one taps the 57 circle on the neck. This helps the ketchup flow by applying the correct shearing force.[44] These techniques work because of how pseudoplastic fluids behave: their viscosity (resistance to flow) decreases with increasing shear rate. The faster the ketchup is sheared (by shaking or tapping the bottle), the more fluid it becomes. After the shear is removed the ketchup thickens to its original viscosity.

Ketchup is a non-Newtonian fluid, meaning that its viscosity changes under stress and is not constant. It is a shear thinning fluid which means its viscosity decreases with increased shear stress.[45] The equation used to designate a Non-Newtonian fluid is as follows: ${\displaystyle \eta =\tau /{\dot {y}}}$. This equation represents apparent viscosity where apparent viscosity is the shear stress divided by shear rate. Viscosity is dependent on stress. This is apparent when you shake a bottle of tomato sauce/ketchup so it becomes liquid enough to squirt out. Its viscosity decreased with stress.[46]

Graph representation of the three main fluid viscosity categories

The molecular composition of ketchup is what creates ketchup's pseudoplastic characteristics. Small polysaccharides, sugars, acids, and water make up the majority of the metastable ketchup product, and these small structures are able to move more easily throughout a matrix because of their low mass. While exposed to shear stress, the molecules within the suspension are able to respond quickly and create an alignment within the product.[47] The bonds between the molecules are mostly hydrogen bonds, ionic interactions, and electrostatic interactions, all of which can be broken when subject to stress. Hydrogen bonds are constantly rearranging within a product due to their need to be in the lowest energy state, which further confirms that the bonds between the molecules will be easily disrupted. This alignment only lasts for as long as shear stress is applied. The molecules return to their original disorganized state once the shear stress dissipates.[47]

In 2017, researchers at the Massachusetts Institute of Technology reported the development of a bottle coating that allowed all the product to slip out without leaving a residue.[48]

## Separation

Ketchup is one of the many products that is leachable; meaning that the water within the product migrates together as the larger molecules within the product sediment, ultimately causing water to separate out. This forms a layer of water on top of the ketchup due to the molecular instability within the product.[49] This instability is caused by interactions between hydrophobic molecules and charged molecules within the ketchup suspension.

Pectin is a polysaccharide within tomatoes that has the ability to bind to itself and to other molecules, especially water, around it. This enables it to create a gel-like matrix, dependent on the amount within the solution. Water is a large part of ketchup, due to it being 80% of the composition of distilled vinegar. In order for the water within the ketchup to be at the lowest possible energy state, all of the hydrogen bonds that are able to be made within the matrix must be made.[50] The water bound to the polysaccharide moves more slowly within the matrix, which is unfavorable with respect to entropy.[49] The increased order within the polysaccharide-water complex gives rise to a high-energy state, in which the water will want to be relieved. This concept implies that water will more favorably bind with itself because of the increased disorder between water molecules. This is partially the cause for water leaching out of solution when left undisturbed for a short period of time.

Other interactions that induce leaching are electrostatic and ionic interactions. Electrostatic interactions occur between charged molecules, which have repulsive or attractive forces between each other. The pectin within ketchup will have negative and neutral charges along the molecule due to the hydroxyl groups and relative pH, which is 3.9 on average.[51] Pectin is most stable at a pH of 3.5, so the more basic pH within ketchup will protonate the hydroxyl side chains and therefore create a less viscous gel. Acetic acid within vinegar also has hydroxyl groups that will have a dispersed amount of negative and neutral charges along each molecule. The acetic acid and pectin will display repulsive interactions between the negatively charged oxygens on each molecule. The hydroxyls on each molecule will be able to form hydrogen bonds with the water in the product. The addition of salt will reduce the repulsive interactions between the negatively charged side chains of acetic acid and pectin within solution because they will create bonds with the dissociated sodium and chloride ions.[52] The hydrogen bonds and electrostatic interactions will encourage leaching because the formation of bonds associated with the need for molecules to be in the lowest energy state are not always bonds that happen between different molecules and instead are formed between like molecules, causing aggregation.

## References

1. ^ Smith, Andrew F. (1996). Pure Ketchup: A History of America's National Condiment, with Recipes. University of South Carolina Press. p. 17. ISBN 978-1-57003-139-7. Retrieved October 1, 2013.
2. ^ "Ketchup: A Saucy History". History. July 20, 2012. Archived from the original on April 2, 2018. Retrieved March 15, 2013.
3. ^ Charles, Dan (September 2, 2019). "Meet The Man Who Guards America's Ketchup". National Public Radio. Retrieved 3 September 2019.
4. ^ a b "How ketchup is made". Made how. Retrieved May 27, 2010.
5. ^ "Behind the Label: tomato ketchup". The Ecologist. Retrieved July 8, 2014.
6. ^ Javier E. David (2013-02-15). "The Ketchup War that Never Was: Burger Giants' Link to Heinz". CNBC.com. Retrieved 2017-03-11.
7. ^ a b In the Chinese Amoy dialect, "kôe-chiap" (Xiamen accented Amoy) or "kêchiap" (probably Penang Hokkien, which is based on Zhangzhou accented Amoy) (part of the Ming Na language) signifies "brine of pickled fish or shell-fish" (Oxford English Dictionary, Douglas Chinese Dict. 46/1, 242/1).
8. ^ a b Jurafsky, Dan (2 September 2009). "Ketchup". The Language of Food. Retrieved November 10, 2011.CS1 maint: ref=harv (link)
9. ^ a b "Ketchup - Definition and More from the Free Merriam-Webster Dictionary". Merriam-webster.com. Retrieved August 26, 2011.
10. ^ https://archive.org/stream/cu31924026564504#page/n35/mode/2up/search/catchup
11. ^ Smith, Andrew F. (1996). Pure Ketchup: A History of America's National Condiment, with Recipes. Univ of South Carolina Press. ISBN 9781570031397.
12. ^ Cooke, Mordecai Cubitt (1891). British Edible Fungi. Kegan Paul, Trench, Trübner & Company Limited. pp. 201–206.
13. ^ Bell, Annie (June 5, 1999). "Condiments to the chef". The Independent. Retrieved September 10, 2014.
14. ^ Branston, Thomas F. (1857). The hand-book of practical receipts of every-day use. Lindsay & Blakiston. pp. 148–149.
15. ^ a b c d "The Cosmopolitan Condiment". slate.com. Retrieved January 30, 2015.
16. ^ Smith, Andrew F. (1996). Pure Ketchup. Univ of South Carolina Press. pp. 16–17. ISBN 978-1570031397.
17. ^ The Independent June 5, 1999, Condiments to the Chef
18. ^ Elizabeth Rozin (1994). The Primal Cheeseburger. New York: Penguin books. ISBN 978-0-14-017843-2.
19. ^ a b "Tomato History: From Poison to Obsession". Archived from the original on 2011-06-13. Retrieved 2011-05-26.
20. ^ Skrabec, Quentin R., Jr. (2009). H. J. Heinz: A Biography. Jefferson, NC: McFarland & Co. p. 56. ISBN 978-0-78645332-0. Retrieved January 26, 2015.
21. ^ Skrabec, Quentin R., Jr. (2009). H. J. Heinz: A Biography. Jefferson, NC: McFarland & Co. p. 57. ISBN 978-0-78645332-0. Retrieved January 26, 2015.
22. ^ "Heinz - History". H.J. Heinz Co. Retrieved July 27, 2011.
23. ^ Casey, Kathy (2004). Retro Food Fiascos: A Collection of Curious Concoctions. Collectors Press. p. 128. ISBN 978-1-888054-88-0.
24. ^ Santich, Barbara, ed. (2012). Bold Palates: Australia' Gastronomic Heritage. ISBN 9781743050941. Retrieved 16 June 2017.
25. ^ Smith, Andrew F. (2013). The Oxford Encyclopedia of Food and Drink in America. Oxford University Press USA. p. 54. ISBN 9780199734962.
26. ^ Gladwell, Malcolm (2009). What the Dog Saw and Other Adventures. Little, Brown & Co., New York, p. 41.
27. ^ Andrew F. Smith (2001). The Tomato in America: Early History, Culture, and Cookery. University of Illinois Press. ISBN 978-0-252-07009-9.
28. ^ Nassauer, Sarah (September 19, 2011). "Old Ketchup Packet Heads for Trash". The Wall Street Journal. Retrieved October 19, 2012.
29. ^ "Heinz unveils new blue ketchup". USA Today. Associated Press. April 7, 2003.
30. ^ Heinz - Consumer FAQs Archived November 20, 2008, at the Wayback Machine
31. ^ "Slice of Sauce:A No-Mess "Slice" of Ketchup". Kickstarter. Kickstarter. June 22, 2018.
32. ^ "Sliced Ketchup Is Here to Keep All Your Sandwiches Mess-Free and It's Already Polarizing". Time. Time. March 23, 2018.
33. ^ "Catsup vs Ketchup". July 2014.
34. ^ De Kleine, John, ed. (2009). Lots Of Fat And Taste Recipes. p. 477. ISBN 9781462834389. Retrieved 16 June 2017.
35. ^ a b "The etymological origin of the word ketchup is a matter of confusion". Pure Ketchup, by Andrew F. Smith, ISBN 1-56098-993-9. Page 4.
36. ^ South China Morning Post article
37. ^ "Ketchup". The American Heritage Dictionary of the English Language, 4th edition, published by Houghton Mifflin Company
38. ^ Yang, Kassim (1994). Kamus Minerva. Seremban.
39. ^ Eugene N. Anderson. The Food of China. (New Haven: Yale University Press, 1988; ISBN 0300047398), p. 160.
40. ^ Mitchell, Christine M. "Book Review: The Handy Homemaker, Eighteenth-Century Style" (PDF). JASNA News (Spring 2010). Archived from the original (PDF) on October 10, 2010. Retrieved March 26, 2015.
41. ^ "Ketchup – Tomato Ketchup". Heinz Ketchup. Retrieved December 15, 2016.
42. ^ "Textural Modification of Processing Tomatoes" (PDF). Retrieved May 19, 2011.
43. ^ "National Nutrient Database for Standard Reference". USDA. Retrieved December 3, 2007.
44. ^ "What's the best way to get Heinz® Ketchup out of the iconic glass bottle?". Archived from the original on November 5, 2012. Retrieved November 5, 2012.
45. ^ "Non-Newtonian fluids". Sciencelearn Hub. Retrieved October 12, 2016.
46. ^ "Shear Mystery | Science Mission Directorate". science.nasa.gov. Retrieved October 12, 2016.
47. ^ a b Coupland, J (2014). An Introduction to the Physical Chemistry of Food. Springer. p. 128.
48. ^ "Slippery bottle solves ketchup problem". BBC (London). February 22, 2017. Retrieved March 7, 2017.
49. ^ a b Vilgis, T. 1893. Nineteen: "Ketchup as Tasty Soft Matter". The Kitchen as Laboratory: Reflections on the Science of Food and Cooking. New York: Columbia University Press. 142–145
50. ^ Journel, A.G., Deutsch, C. V., Entropy and spatial disorder. Mathematical Geology. Volume 23, Is. 3. April 1993. 329-355.
51. ^ Porretta, S., Analytical Profiling of Ketchup. Journal of the Science of Food and Agriculture. Volume 57. 2006. 293-301.
52. ^ Schwarz, U. Theory of soft biomatter. June 2009. 19-65