Chocolate Crystals and what's up with Tempering

I’m trying to lay out a “big picture” that logically incorporates all the info out there about chocolate tempering. I have found articles that go into depth about the underlying chemistry of chocolate, without really conveying an understanding that is helpful in tempering. I have also found many tempering methods described that include contradictory and/or confusing explanations about what is going on in the chocolate.

Trying to follow any particular method for tempering can give one person consistently great results, while another may fail to get that right temper consistently, if at all. This suggests some important information was left out of the instruction, leaving part of the process up to random chance. The step most often overlooked is the temperature of the room where chocolate is "set". Being too warm or too cold can ruin an otherwise well-executed process.

I believe this confusion and inconsistency is what makes tempering seem so mysterious and frustrating. Understanding tempering fully can help demystify chocolate, and free you to trouble-shoot and modify the process to suit your personal preferences. The following info is my internet research and personal experience folded together to build a consistent story for how chocolate behaves. Please leave comments if anything comes across unclear or inaccurate.

A new batch, tempered using cocoa butter "silk"

First batch. Started out tempered, but turned to type VI when "setting"
 in a room that was too warm. Flavor and texture were affected.

From same batch, left out for a few days more. 
Fully Type VI, grainy and terrible. This one
has Rice Krispies in it.

Same batch, re-tempered and "set" in a cooler room; still has some
 bloom, maybe from the molding process, or "set"room still not cool
enough. Tasted great, with a nice snap and mouth-feel.

Same batch, re-tempered again, and "set" in an even cooler room, ~60°F.
 Looking very nice! Still some discoloration in the corners. Tasted great,
with a nice snap and mouth-feel.

Basics:

Cocoa butter can crystalize in six different structures. The crystals begin to form in liquid chocolate. Full crystallization makes the bar become solid. Only type V crystals give that glossy, snappy, melt-in-your-mouth bar of goodness known as tempered chocolate. Types I - IV have a lower melting temperature and lack the shine, snap, and mouth-feel; Type VI is brittle, grainy, doesn’t melt in the mouth, and has muted flavor. Chocolate tempering is all about forming the Type V crystals in melted chocolate, so that the solid bar will also be Type V.

Many methods achieve tempered chocolate. Some methods only work for special cases. The general approach is:

1.    Melt all crystals.

2.    Generate or add the good (Type V) crystals as the chocolate cools.

3.    Re-heat to melt any undesirable (Type I-IV) crystals that might have snuck in at the lower temperatures.

4.    Set the liquid chocolate in a cool place to crystalize and solidify: cool enough to prevent Type VI; not so cold as to cause condensation or to favor Type I - IV crystal growth.

Water and Chocolate:

1.    Adding water to melted chocolate will make the chocolate seize, becoming lumpy and grainy. This is because the sugar attempts to dissolve into not-enough water. Find a more complete explanation here. Seized chocolate cannot be tempered or turned into bar candy. Add enough liquid (cream is great!) for it to smooth out again, and use it as a chocolate sauce or ganache.

2.    Water droplets on “set” chocolate can cause “sugar bloom” by dissolving sugar from the chocolate. The sugar recrystallizes as the water dries, causing a “bloom” mark that looks about the same as cocoa butter bloom. To avoid this, prevent condensation on your chocolate by being careful with temperature and humidity changes while setting, storing and handling.

Temperatures of note:

1.    >200°F: Chocolate will scorch/burn, and is not recoverable.

2.    115° to 130°F?: At some undefined temperature, probably in the range listed, chocolate will :break” or separate, becoming a pool of thin yellow cocoa butter with dark lumps of cocoa solids sitting in it. This chocolate can no longer be tempered into bars; theoretically adding lecithin might make it mix back together and work as a bar, otherwise treat it like seized chocolate.

3.    >97°F: All crystal types melt. Full melting occurs faster at higher temps.

4.    93°F to 95°F: The good crystals (Type V) melt. Full melting is gradual, not instant.

5.    84°F to 93°F is the “sweet spot” for the good crystals (Type V), where they form slowly but spontaneously, and Type I - IV will gradually melt.

6.    92°F: Preferred holding temperature for tempered chocolate.

7.    61°F to 84°F: “Bad” crystals Type I - IV can form spontaneously, each at the temperatures listed in the table.

8.    59°- 68°F: “Good” range for letting chocolate “set”. A warmer room may cause crystals to convert to Type VI, which is bad.

9.    59°-64°F: optimal long term storage temperature.

 

Crystal	Melting/Forming Range
Type I	61° to 67° F
Type II	70° to 72° F
Type III	78° F
Type IV	81° to 84° F
Type V	93° to 95° F
Type VI	97° F

Other Details:

1.    Stirring causes existing crystals to grow faster. Stirring also distributes heat, which can help melt crystals faster if the temperature is rising above their melting point.

2.    Whatever crystals are present in the liquid chocolate will grow as it cools, or “sets”.

3.    Chocolate can be re-tempered as many times as you like.

4.    Some tempering methods result in more crystals in the melted chocolate than others; more crystals = thicker; less crystals = thinner. Use the most convenient tempering method that gives what you want. Thin is usually better for dipping or coating; thick is needed for “kiss” shapes.

5.    Sooner or later, chocolate will lose its temper, as the Type V crystals transform to the more stable Type VI. Delay this transition by storing at 59°-64°F.

6.    Trying to “set” well-tempered chocolate in a room that is too warm (>68°F) can result in “bloom”, and can be rapidly followed by formation of type VI crystals.

7.    Chocolate that has melted or softened (in a car or a pocket, for example) and then been put in the fridge to harden again results in Type VI crystals.

 

References:

Chocolate Alchemy
Feedback I got in a Reddit thread, especially from user Snoron, who recommended the easiest way to get good temper.
https://chocolatealchemy.com/how-to-make-cocoa-butter-silk/
https://crystallography365.wordpress.com/2014/06/14/the-chocolate-you-dont-want-cocoa-butter-form-vi/ 
The Polymorphs of Chocolate – Compound Interest
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4403828/ 
https://acselementsofchocolate.typepad.com/elements_of_chocolate/TEMPERINGCHOCOLATE.html
https://www.chemistryviews.org/details/ezine/808827/Chocolate__The_Noblest_Polymorphism_II.html 
https://wwwf.imperial.ac.uk/blog/physics-of-cooking/2014/12/19/exploring-the-polymorphic-structures-in-milk-chocolate-dark-chocolate-and-cocoa-butter/
http://www.dandelionchocolate.com/2017/09/21/a-note-about-tempering/
https://www.scienceofcooking.com/chocolate/why-is-chocolate-tempered.htm
https://chemistry.stackexchange.com/questions/94101/what-do-the-six-polymorphs-of-chocolate-look-like
https://www.compoundchem.com/2014/04/19/the-polymorphs-of-chocolate/