Question: What causes properly processed chocolate to have a nice sheen and crisp bite?
About the article "Chocolate", section "Tempering".

Candidate passages:
The final process is called "tempering".
Uncontrolled crystallization of cocoa butter typically results in crystals of varying size, some or all large enough to be clearly seen with the naked eye.
This causes the surface of the chocolate to appear mottled and matte, and causes the chocolate to crumble rather than snap when broken.
The uniform sheen and crisp bite of properly processed chocolate are the result of consistently small cocoa butter crystals produced by the tempering process.
The fats in cocoa butter can crystallize in six different forms (polymorphous crystallization).
The primary purpose of tempering is to assure that only the best form is present.
The six different crystal forms have different properties.
As a solid piece of chocolate, the cocoa butter fat particles are in a crystalline rigid structure that gives the chocolate its solid appearance.
Once heated, the crystals of the polymorphic cocoa butter will be able to break apart from the rigid structure and allow the chocolate to obtain a more fluid consistency as the temperature increases.
This is known as the melting process.
When the heat is removed, the cocoa butter crystals will become rigid again and come closer together, allowing the chocolate to solidify.
This temperature in which the crystals obtain enough energy to break apart from their rigid conformation would depend on the milk fat content in the chocolate and the shape of the fat molecules as well as the form of the cocoa butter fat.
Chocolate with a higher fat content will melt at a lower temperature.
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.
Generally, the chocolate is first heated to to melt all six forms of crystals.
Next, the chocolate is cooled to about , which will allow crystal types IV and V to form.
At this temperature, the chocolate is agitated to create many small crystal "seeds" which will serve as nuclei to create small crystals in the chocolate.
The chocolate is then heated to about to eliminate any type IV crystals, leaving just type V. After this point, any excessive heating of the chocolate will destroy the temper and this process will have to be repeated.
However, there are other methods of chocolate tempering used.
The most common variant is introducing already tempered, solid "seed" chocolate.
The temper of chocolate can be measured with a chocolate temper meter to ensure accuracy and consistency.
A sample cup is filled with the chocolate and placed in the unit which then displays or prints the results.
Two classic ways of manually tempering chocolate are:
 Working the molten chocolate on a heat-absorbing surface, such as a stone slab, until thickening indicates the presence of sufficient crystal "seeds"; the chocolate is then gently warmed to working temperature.
 Stirring solid chocolate into molten chocolate to "inoculate" the liquid chocolate with crystals (this method uses the already formed crystals of the solid chocolate to "seed" the molten chocolate).
Chocolate tempering machines (or temperers) with computer controls can be used for producing consistently tempered chocolate, particularly for large volume applications.
  Chocolate – raw or processed food produced from the seed of the tropical "Theobroma cacao" tree.
The seeds of the cacao tree have an intense bitter taste, and must be fermented to improve the flavor.
Chocolate is a popular ingredient in confectionery items and candies.  
Couverture chocolate is a very high quality chocolate that contains extra cocoa butter (32-39%).
The higher percentage of cocoa butter, combined with proper tempering, gives the chocolate more sheen, firmer "snap" when broken, and a creamy mellow flavor.
The total "percentage" cited on many brands of chocolate is based on some combination of cocoa butter in relation to cocoa solids (cacao).
In order to be properly labeled as "couverture", the product must contain not less than 35% totaldry cocoa solids, including not less than 31% cocoa butter and not less than 2.5% of dry non-fat cocoa solids ; Couverture is used by professionals for dipping, coating, molding and garnishing.
The term "couverture chocolate" should not be confused with compound chocolate.
Products that contain compound chocolate have a lower percentage of solids and contain non-cocoa fats.
Some brands of couverture chocolate are packaged tempered, and others are packaged untempered.
Subsequent tempering may or may not be required, depending on the usage and the desired characteristics of the final product.
Couverture chocolate should not be substituted when semi-sweet, bittersweet, or unsweetened chocolate is called for in a recipe, as the increased cocoa butter content and the sugar content may alter the finished product. 
 You can’t have cookies for breakfast, but you can have Cookie Crisp!
(1977–1983) If you like cookies, you’ll love Cookie Crisp!
(1983–1990) No other cereal tastes like this.
(1990–1996) It’s like lots and lots of little chocolate chip cookies!
(1996–2001) Now with a mouthful of chips, in every bite.
(2001–2005) Coooookie Crisp!
Next time, it’s mine!
(2005–2007) (Still used in the UK and Ireland.)
Totally Chip-alicious!
(2007–Present)  
Arnott's are well known in Australia and internationally for producing several quintessentially Australian biscuits.
Some of their major products include: Caramel Crowns: a plain biscuit, topped with caramel, and covered in chocolate.
Cheds: a savoury cracker that is perforated and sprinkled with cheddar cheese and salt.
Chocolate Butternut Snap: a crunchy oatmeal and coconut biscuit covered in chocolate.
Chocolate Dessert: a chocolate cream sandwiched between two chocolate biscuits.
Discontinued in 2005 due to low sales.
Choc Monte: a golden syrup, honey and coconut biscuit covered in dark chocolate.
Chocolate Ripple: a chocolate-flavoured biscuit that is commonly used by Australian home cooks as the basis of 'Chocolate Ripple Cake' by adding layers of freshly whipped cream between each layer of biscuit and covering the whole construction in more cream and is then refrigerated overnight.
Chocolate Royals: a vanilla biscuit topped with various flavours of marshmallow coated in dark or milk chocolate, similar to the Scottish Tunnock's teacake or New Zealands mallowpuffs.
The royal comes in two versions.
Dark chocolate (with white marshmallow) or milk chocolate (with pink marshmallow)  Chocolate Wheaten: a new product acquired after Campbell's takeover.
A round, semi-sweet, whole wheat flour biscuit covered in either milk chocolate or dark chocolate.
Brand acquired from George Weston Foods in 2003.
Coconut Rings: a coconut biscuit shaped in a ring.
Discontinued after Campbell's takeover.
Cruskits: a large rectangular crisp snack bread very much like French toast, available in Original, Wholemeal & Rice varieties.
Custard Cream: a custard cream filling sandwiched between two rectangular vanilla biscuits.
Delta Cream: two round chocolate biscuits with vanilla cream in the middle, similar to an Oreo, but sweeter and not so much cocoa.
Golliwog / Scalliwag: a biscuit made in the shape of the Golliwogg toy, which was first sold in the 1960s and popular at that time.
The name was changed to Scalliwag in the mid-1990s, however the biscuits remained in the shape of a Golliwog and the product was discontinued by the late 1990s.
They made a reappearance in shops in 2010 but seem to have been removed from production again.
Honey Jumbles: small honey gingerbread cakes, topped with pink or white icing.
Iced Animals: created by the new owner Robert Arnotts, animal shaped biscuits with pink, green, yellow, and orange icing on top.
Iced Vovos: a wheat flour biscuit with a raspberry jam and fondant topping sprinkled with coconut.
Jatz: a round savoury crisp cracker, lightly salted, also available in a cracked pepper flavoured variety.
Clix: a round savoury cracker but more buttery and saltier than Jatz with a softer texture.
Kingstons: small round coconut biscuits with chocolate cream in the middle.
Lemon Crisps: two sweet crackers with a light sprinkling of salt and lemon cream sandwiched in between.
Marie: a plain sweet, vanilla-flavoured biscuit similar to a rich tea biscuit.
Milk Coffee: a sweet biscuit with a hint of coffee flavouring.
Milk Arrowroot: historical flagship biscuit brand of Arnott's, made with Arrowroot flour, commonly given to babies to introduce them to solid food.
Mint Slice: a round chocolate biscuit topped with mint flavoured cream and coated in dark chocolate.
Also available in Mandarin, Tia Maria and Coconut flavours.
Monte Carlo: a raspberry and cream fondant sandwiched between two golden syrup, honey and coconut biscuits.
Nice: a sweet biscuit covered with granulated sugar.
Orange Creams: two vanilla biscuits with orange cream in the middle.
Quatro: chocolate-coated biscuits with toppings such as fruit and nut, or caramel.
Brand acquired from George Weston Foods in 2003.
As of late 2010, no longer in production.
Raspberry shortcake: a biscuit base with raspberry filling then topped with a doughnut shaped biscuit and sprinkled with granulated sugar SAO: a large square-shaped, plain cracker biscuit.
The name stands for "Salvation Army Officer" as the biscuit was made especially for the Salvation Army Officers of the day as a snack that they could carry with them on their visiting rounds.
Salada: a salted crisp cracker, rectangular in shape but with perforations down its centre to allow it to be halved for "hors d'oeuvres".
Originally a Brockhoff product.
Savoy: a crispy cracker.
Originally only sold in Victoria, South Australia, and Tasmania but later available in New South Wales, ACT, and Queensland.
Originally a Brockhoff product.
Scotch fingers: shortbread biscuit, also available in chocolate-coated variety.
Sesame wheats: savoury cracker topped with toasted sesame seeds.
Shapes: a savoury cracker with sprinkled flavourings.
Sold in various varieties such as Barbecue, Pizza, Cheddar, Chicken, Nacho Cheese and Cheese & Bacon.
Shortbread creams: two vanilla shortbreads with vanilla cream in the centre.
Strawberry tarts: a tart base with strawberry jam in the centre.
Teddy Bear Biscuits: biscuits shaped like a teddy bear.
Also comes in a chocolate coated variety.
They are a different product to Tiny Teddies.
TeeVee Snacks: a bite-sized chocolate coated biscuit, promoted as being ideal for TV snacking.
Tic Tocs: clock-shaped iced vanilla biscuits, with clock faces embossed on the underside.
Tim Tams: a two-layered oblong chocolate-coated biscuit originally with a chocolate cream filling.
Flavours now include milk chocolate, white chocolate, dark chocolate, double coating of chocolate, caramel centred, chilli, coconut, berry filling (Pink Wish charity edition), Kahlua, Love Potions series (chocolate and raspberry, vanilla and toffee, choc mud) and latte filling.
The latest flavour to be released in 2008 is orange.
Tina Wafer: a sweet cream sandwiched between two light wafers.
Varieties include chocolate, strawberry and vanilla.
Tiny Teddies: thumb-sized teddy bear-shaped snacks.
Practically identical to the American Nabisco brand Teddy Grahams Venetians: a sweet round biscuits with chewy dried blueberries.
One side dipped in a sweet white chocolate syrup.
Vita-Weat: wholewheat crisp bread available in original and sandwich size.
Wagon Wheels: marshmallow and jam sandwiched between two round biscuits, coated in chocolate (original variety); also now available with chocolate fudge in place of jam (double choc variety).
The original brand was acquired from George Weston Foods in 2003.
Water crackers: original, sesame and cracked pepper.
Yo-Yo: a sweet biscuit made with butter, eggs, milk and honey, originally baked by Menz in South Australia.