HomeGeneralChocolate Tempering: Beta Crystal Nucleation and the Purple Haze Phenomenon

Chocolate Tempering: Beta Crystal Nucleation and the Purple Haze Phenomenon

(This article appeared in the Spring 2022 issue of Pastry Arts Magazine)

by Dennis Teets

“Look for the purple haze – do you see it?!” “What purple haze?” I muttered back at the scientist who was training me on how to temper chocolate. I looked and I looked, until finally I thought I saw what he was looking at on the surface of the chocolate I had just tempered: a slight purple haze. I would like to say that from that time forward I easily saw the elusive purple haze every time I tempered chocolate, but it took a while for my eyes to be able to pick it up. However, learning to identify this haze and other characteristics of a well-tempered chocolate has saved me many hours and much frustration over the years.

While there are different fat systems used in making chocolate, cocoa butter is the one that gives the most decadent eating experience. The reason for this is that cocoa butter is completely melted at the human’s body temperature of 98.6°F (37°C). However, cocoa butter is a polymorphic fat. A polymorphic fat is a fat that can solidify with different melt points depending on the temperature at which it was nucleated. There are six different polymorphic states a cocoa butter can nucleate as, according to R.L. Willie and E.S. Lutton, chemists and authors of the Polymorphism of Cocoa Butter (1966). These states are classified as Form I to Form VI. Tempering is the act of bringing a chocolate to a specific temperature while creating sufficient Form V nuclei to cause non-Form V crystals to transform into a Form V crystals upon solidification. This action causes the solidified chocolate to have a specific melt-point and other favorable texture characteristics. The first four forms all create a solidified chocolate that will melt quickly when touched, be dull in appearance, and have a soft texture. Form VI leads to white fat crystals that come to the surface over time and negatively affect both appearance and texture. However, Form V crystals result in a chocolate that contracts and releases from a mold, has a nice shine or even a gloss if formed in a smooth shiny mold cavity, breaks cleanly with a snap, and has a very smooth melt in the mouth.

Getting a chocolate to form Form V nuclei is a relatively easy process, as it is based on forming the nuclei at a specific temperature. Controlling the number and growth of these nuclei to modify the flow properties of a tempered chocolate during use is a more difficult process, as it is a dynamic one requiring temperature adjustment to maintain not only the proper type of crystals, but also the proper number and size to ensure the best flow properties for the project being performed. For a molded product, the chocolate must be thin enough flow into the details of fine crevasses of the mold cavity. For a dipped or enrobed product, the chocolate must be thick enough that only a small amount of chocolate flows off the piece and thus has the ability to create a rim at the base of the product upon solidification.

The Tempering Process: Nucleation of Form V Crystals

The initial stage of a tempering process is the formation of Form V nuclei. From these nuclei, Form V crystals will grow. There are two types of nucleation that occur in chocolate tempering: Primary and Secondary. Understanding these two types will allow the chocolatier to have some control over both the initial thickness and the thickening of the chocolate over the time it is being used. In the rest of this article, we will look at nucleation from the standpoint of how to initiate it to obtain Form V crystals.

In a primary nucleation system, the supply chocolate is brought down in temperature between 78°F (25.5°C) and 82°F (27.7°C), and then sheared on a cold slab, 65°F (18.3°C) to 70°F (21.1°C), until it thickens. This thickened but still flowable chocolate mass is then placed back into the molten chocolate when it is at a temperature at the lower end of the Beta crystal development temperature range, 83°F (28.3°C) to 89°F (31.6°C). These types of systems include continuous systems like a four-zone tempering unit.

In a secondary nucleation system, seed chocolate is dispersed into the melted chocolate at a temperature at which Form V crystals have not fully been melted. The seed chocolate comes from solidified commercial chocolate. A manual example of this system would be melting about 75 percent of a commercial chocolate to a temperature high enough to melt out all previously formed seed and then adding a block of the chocolate as seed chocolate at about 25 percent of the total batch weight. The seed chocolate is allowed to melt-in as the supply chocolate’s temperature drops to below the melting point of Form V crystals. Note that un-melted seed chocolate must be present at this temperature in a range of one to four percent for the fully melted chocolate’s cocoa butter to transform into enough Form V crystals to solidify with the desired characteristics. The best way to ensure this is to be certain that there is a small amount of solid chocolate that needs to be removed prior to using the chocolate.  Revolving bowls systems (like Chocovision, ACMC, and Hillards) and static melt pots are examples of secondary nucleation systems.

Early Identification of a Tempered Chocolate for the Presence of Form V Crystals

Whether you are using a primary or secondary nucleation system, learning to identify when a paste has enough Form V crystals to produce the desired finished product will save you time, frustration, and money.

If the basic parameters listed above are followed, a chocolate can be tempered using a wide variety of methods. The key is to define the parameters that give you the best results for your use of the chocolate. The first part of working with chocolate is learning how to identify when it is nucleated to have enough Form V crystals to obtain a well-tempered solidified product.  I use the following two tests when I work with chocolate.

  1. Visual Evaluation for Light Reflection and Texture Changes

The purple haze seen in the picture to the left happens because of the way light reflects through liquid chocolate containing Form V crystals. In conjunction with light reflection there is also a texture change. This change is enhanced by writing or drawing on the surface of the chocolate with other chocolate from the bowl using a spatula as a brush. In picture #1 you can easily see the purple haze in the lower left-hand corner of the picture as a change in color and texture. In pictures #2 and #3, a well-tempered chocolate is compared to an un-tempered chocolate.  In picture #2, notice the purple-like reflection, especially on the ridges, as well as a dull haze in other places. Also note how high and well defined the ridges are when compared to those in picture #3. This is due to the stacking of Form V crystals as they grow and interact more and more with each other. In picture #4, note a general haze (matte shine) with some purple hues.

As seen in the pictures, both texture and reflection are indicative of a well-tempered chocolate, but are not always easily seen. Because of this, when in doubt I take the time to run a solidification test on a whole item or use the following Five-minute Plastic Spoon Solidification Test.

  1. Five-minute Plastic Spoon Solidification Test
7. Seed vs Non-seeded Dark Chocolate Five-Minute Test – Grain

Take a flexible plastic spoon and dip it in the chocolate to be tested so that about ½ to 3/4 inch of the spoon is coated in chocolate. Place the spoon on a piece of parchment paper so the chocolate is not touching the paper and place in a refrigerator for five minutes. If well-tempered, the chocolate will be hard to the touch (A) and move from a wet shine (B) to matte shine (A). The chocolate will break free from the spoon cavity (C) when either pushed or twisted, instead of not releasing from the spoon cavity (D) and finger printing (D). The released chocolate will have the gloss of the spoon cavity (C). When broken, the piece released from the spoon will have a fine grain (E). Note, the chocolate above was a dark chocolate, white and milk might take as long as 10 minutes. Untempered chocolate will smear when touched and not release from the cavity.

About Dennis Teets

Dennis Teets has worked in the confectionary industry for both large and small organizations for over 30 years. During that time, he was both a problem solver and a new product developer. Today, Dennis works as a coach and consultant for small to medium chocolate companies, focusing on growth, scale-up and problem solving. His email is [email protected]

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