STUFF MATTERS: Chapters 4-6

CHAPTER 4: DELICIOUS
• On chocolate
• Chocolate is a food concoction designed to be ingested solid and to slowly melt in the mouth.
• One of its main ingredients is cocoa butter whose properties contribute to the overall sensation, flavor, and texture of chocolate:
o Its melting point is close to body temperature.
o It contains antioxidants that help reduce oxidation of the fats resulting in rancidity prolonging the shelf-life (“can be stored for years” according to the author).
o It forms crystals which give chocolate its mechanical strength.  The different ways that the triglycerides pack result in different types of crystals.  Types I and II are mechanically soft and quite unstable with a low melting point of 16 C making them easy to mold, harden, and remelt (like ice scream coating).  Types III and IV are denser but also soft and crumbly and do not snap upon breaking.  Type V is an extremely dense fat crystal which has  a glossy, hard surface and snaps when broken.  Its melting point is 34 C which keeps them hard and solid until they are eaten and start to melt in the mouth.
• Dark chocolate is usually % cocoa fat, 20% cocoa powder, and 30% sugar.  Many of the components of cocoa powder are alkaloids and phenolics, like caffeine and theobromine, that are bitter and astringent, activating the “bitter and sour taste receptors and complement the sweetness of the sugar”.
• Chocolate can have up to 600 different molecules.  The fruity ones are likely esters.  As mentioned above, the alkaloids and phenolics like theobromine and caffeine are bitter tasting.
• After harvesting the cocoa beans, they are left out in the heat to decompose and ferment.  The esters are produced during the fermentation process as enzymes catalyze the reaction between acids and alcohols.
• During roasting, several chemical reactions further turn the chemicals into chocolate ingredients.  The roasting process caramelizes the carbohydrates in the bean.  A second reaction at high temperature (160 C or above) is the Maillard reaction wherein sugar, esters, and alcohols react with proteins producing a variety of flavor molecules.   The Maillard reaction causes the “nutty, meaty flavors of chocolate while also reducing some of the astringency and bitterness”.  (The same reaction is responsible for the flavor of bread crust, roasted vegetables, and many other roasted savory flavors.)
• In the further development of chocolate as a solid gustatory treat, milk was added to further remove the bitterness.  Chocolates from different countries differ in flavor and texture mostly because of the type of milk added:  In the US, they use reduced fat milk (removed by enzymes) which gives it a “cheesy, almost rancid flavor”.  In the UK, they use a concentrate of milk to which sugar has been added giving chocolate a “milder caramel flavor”.  In Europe, powdered milk is used giving the chocolate “a fresh dairy flavor with a powdery texture”.
• Cultural significance:  The author has the following to say: “…I truly appreciate that chocolate is one of our greatest engineering creations. It is certainly no less remarkable and technically sophisticated than concrete or steel. Through sheer ingenuity, we have found a way to turn an unpromising tropical rainforest nut that tastes revolting into a cold, dark, brittle solid designed for one purpose only: to melt in your mouth, flood your senses with warm, fragrant, bittersweet flavors, and ignite the pleasure centers of the brain. Despite our scientific understanding, words or formulae are not enough to describe it. It is as close as we get, I would say, to a material poem, as complex and beautiful as a sonnet. Which is why the Linnaean name for the stuff, theobroma, is so appropriate. It means “the food of the gods.”

CHAPTER 5: MARVELOUS
• On Aerogel (a type of foam)
• Samuel Kistler, an American farmer turned chemist, was the first to create and characterize aerogels stimulated by his initial curiosity about jelly, a mostly liquid substance held within a thin mesh of a solid substance.  In gelatin, the thin mesh is made up of polymeric protein (collagen) which, when added to water, the “gelatin molecules unravel and connect with one another to form a mesh that traps the liquid within it” by surface tension.  This surface tension is strong enough to keep the liquid trapped inside the protein mesh but weak enough to move around which gives gelatin the “wobble”.
• In a letter entitled, “Coherent Expanded Aerogels and Jellies” published in the journal Nature in 1931, Kistler wrote: “…The continuity of the liquid permeating jellies is demonstrated by diffusion, syneresis, and ultra-filtration, and the fact that the liquid may be replaced by other liquids of very diverse character indicates clearly that the gel structure may be independent of the liquid in which it is bathed.”  [Syneresis is the contraction of a gel as a result of separating out the liquid.]
• Gel became the general term for mixtures of similar composition (e.g. hair gel, chicken stock, foam, even concrete).
• The biggest challenge in making of an aerogel is the removal of the liquid from the gel’s internal skeleton without causing the gel to simply collapse and shrink.  Kistler and collaborators got around this by raising the temperature and pressure of the liquid to its critical point at which the liquid and its gas state have the same density and structure.  At this point, the whole liquid becomes a gas even though the “jelly has had no way of ‘knowing’ that the liquid within its meshes has become a gas”.  The gas is allowed to escape slowly leaving an intact silica aerogel with a silicon dioxide (essentially glass) skeleton.
• Silica aerogel has the following properties:
• It is the least dense solid known (with a density three times that of air) composed of 99.8% air.
• It looks transparent like glass when light goes through it as the very small amount of material causes so little distortion.  When against a black background, it looks blue as it scatters light (just like our atmosphere which makes our sky look blue due to Rayleigh scattering).
• It has extremely effective thermal insulating capacity protecting a flower sitting on its surface from the heat of a bunsen burner flame less than half a centimeter away.
• Despite the wonder properties of aerogel, it has seen only esoteric uses due to its high manufacturing cost.  It is used in some specialized cases.  It has also been used to capture stardust, its highly durable structure being able to withstand the impact of particles travelling at 50 km/s (or 18,000 km/hr) without breaking apart.
• The author offers the following tribute to aerogel and its wonder: “Aerogels were created out of pure curiosity, ingenuity, and wonder. In a world where we say we value such creativity, and give out medals to reward its success, it’s odd that we still use gold, silver, and bronze to do so. For if ever there was a material that represented mankind’s ability to look up to the sky and wonder who we are, if ever there was a material that represented our ability to turn a rocky planet into a bountiful and marvelous place, if ever there was a material that represented our ability to explore the vastness of the solar system while at the same time speaking of the fragility of human existence, if ever there was a blue-sky material—it is aerogel.”

CHAPTER 6: IMAGINATIVE
• On plastic
• When billiard known as pool in the US started to become popular, there was a concern about depleting source of ivory, the substance of which the balls are composed.  Ivory has properties well suited for the game of billiard or pools:
o Hardness that can withstand denting or chipping upon collision
o Overall internal structural integrity to preventing cracking
o Ability to be machined into a sphere
o Ability to absorb dye for coloring
• Nitroglycerin is produced by nitrating glycerol which occurs when it is mixed with nitric acid.
• Nitrocellulose is a cellulose molecule where the hydroxyl groups have been nitrated.  John Wesley Hyatt made nitrocellulose by mixing wood pulp with nitric acid.  Adding naphtha [which contained the camphor?], derived from crude oil, turns the nitrocellulose in a moldable mixture that hardens into a solid.  He referred to this process as plasticization.
• The author later defines the term plastic “which refers to a huge variety of materials, all of which are organic… solid, and moldable.
• A similar product called xylonite was produced in the same way with the exception that camphor was used instead of naphtha.  This resulted in a patent case as related in a play format by the author.
• Celluloid is known as the first commercial moldable plastic.  It later on was used as a substrate for photographic film for taking still and eventually moving pictures.
• Other plastics that followed include Bakelite, nylon, vinyl, and silicone.
• Cultural significance: the invention of this material which allowed the reproduction of normally expensive material at much lower costs allowed the growing middle class the opportunity to acquire similar materials as the wealthy but affordable.
• In the author’s words at the end of the chapter, the cultural contribution of plastics are immense:  “The plastics that followed celluloid, such as Bakelite, nylon, vinyl, and silicone, built on its creative power and have also had an important impact on our cultural psyche. Bakelite became a moldable replacement for wood at a time when the telephone, radio, and television were being invented and needed a new material to embody their modernity. Nylon’s sleekness took on the fashion industry, replaced silk as the material for women’s stockings, and then spawned a new family of fabrics, such as Lycra and PVC, as well as a group of materials called elastomers, without which all our clothes would be baggy and our pants would fall down. Vinyl changed music, how we recorded it and how we listened to it, and along the way it created rock stars. And silicone—well, silicone turned imagination into reality by creating a plastic form of surgery.”