(This article appeared in the Fall 2022 issue of Pastry Arts Magazine)
By Dennis Teets
I think of myself as a patient person – that is, until it comes to cooling down a fully melted container of chocolate in temperature to the point where powdered chocolate seed can be added to provide Form V crystals for tempering, while still retaining desirable flow properties. In this scenario, I lose my patience, because if I simply place the chocolate in a cool area, I end up forgetting about it and wind up with a lumpy chocolate when I stir the cooler outside chocolate back into the warmer center chocolate. I then have to reheat it to melt out the lumps, while simultaneously trying to maintain/obtain the desired temperature required for seeding. My second, and most chosen, option is to stir the chocolate the whole time it is cooling to prevent lumps from forming, and to me this process seems like it takes forever. The reason for these issues is the polymorphic nature of the cocoa butter in the chocolate, as it must be cooled very uniformly to minimize the formation of lower forms of crystals, which form when the cocoa butter in the chocolate comes in contact with temperatures in the mid 60’s to low 70˚F (18-22˚C). These issues only intensify at lower temperatures. The dilemma is that the greater the difference in temperatures between the cooling environment and the chocolate being cooled, the quicker the chocolate will cool, but also the greater the risk of getting a lumpy or overly thick chocolate as you work the chocolate at lower temperatures. These issues only increase upon the addition of seed. This is especially true when working with small quantities.
So, the choice is either a very slow process with sporadic mixing, or a quick process with continuous mixing and monitoring of the chocolate for temperature and thickness. However, I have learned by creating a controlled heat sink, a chocolate can be cooled both rapidly and with a minimal amount of mixing while maintaining a uniform texture.
What is the purpose of cooling a chocolate before adding seed?
Cooling is simply the removal of sensible heat. Sensible heat is energy either absorbed or released by an object that causes an increase or decrease respectfully of the item’s temperature. Another way of looking at it is temperature is a measurement of sensible heat. When removing sensible heat, the difference in the temperature between the high heat component to the low heat component is very important, as the smaller this difference the longer the time it will take to get the cooling component to the desired temperature. This temperature difference is called the delta.
What is a heat sink?
A heat sink is a device that transfers heat from a higher temperature material to a lower temperature material. Every heat sink has two components: a material from which heat is to be removed, and a component to absorb the heat from the higher temperature material. In a typical room environment chocolate cooling system, chocolate is the material from which heat is being removed. The rooms air is the colder environment used to absorb heat from the higher temperature chocolate. Air is the most used heat sink when manually tempering chocolate. While air is the most used heat sink, it has a low thermal conductivity of 0.024 W/mK, which means it takes a long time to drop the temperature of a chocolate to the temperature required for seeding. This is especially true if coming from a temperature of 110°F (43˚C) or greater to a temperature in the mid-80s to the low-90s (29-33˚C), where the delta is 30-plus degrees. A third component, a container, is required when cooling a liquid material to separate the liquid from the lower temperature component.
In addition to sensible heat being removed as seen by the drop in temperature, any chocolate that encounters temperatures lower than 84°F (29˚C) will begin to form lower forms of cocoa butter crystals. These crystals will begin to rapidly form as the temperatures move further below the melt-point for these crystals. Thus, it is important to limit the contact of the chocolate with these temperature. Typical melt points for the four lower melt point polymorphic forms of cocoa butter crystals are: Form 1, 61-67°F (16-19˚C); Form II, 70 – 72°F (21-22˚C); Form III, 78°F (25˚C); Form IV, 81-84°F (27-29˚C). As these crystals form on the wall of the holding container, the chocolate will begin to thicken. The colder the temperature of the wall, the quicker the chocolate will thicken. Unless stirred, this gradient in thickening will cause lumps to form in the chocolate mass, which can leave the chocolate lumpy even when brought back to the reheat temperature. Removing these lumps can be both difficult and time consuming.
Why you should consider switching to a water-based heat sink for the removal of sensible heat
There are three main reasons to switch to a water-based heat sink. First, because of the higher thermal conductivity, 0.58 W/mK of water verses 0.024 W/mK for air, a product can be cooled in up to 75 percent less time than air-based cooling systems. Second, a lower temperature environment can be created within a warmer room, allowing the system to be used in a wider variety of environments. Third, once cooled, the chocolate temperature can be stabilized until ready for seeding by adding back warmer water at or slightly above the seed addition temperature.
Key principles to getting good results from a water-based heat sink system
- The cooling water temperature should be kept between 65°F and 69°F (18-20˚C). In this temperature range, the cocoa butter will not solidify quickly, yet there is a large enough delta for the chocolate to be cooled relatively quickly.
- Never use temperatures below 65°F (18˚C), as cocoa butter crystals quickly solidify when coming in contact with a surface with a temperature below 65°F, and a lumpy chocolate is likely to occur due to partial solidification of chocolate on the container wall being mixed into the warmer chocolate.
- Use a ceramic or glass container to get more even distribution of heat while preventing a chocolate from solidifying on the container wall. Stainless steel has a thermal conductivity of 15 W/mK, which is about 3.5 times higher than a ceramic cup. This means it would be expected that the cooling chocolate would solidify on the side wall of the stainless cup faster than the ceramic cup.
- Always wipe the chocolate container when removing from the water to prevent water from getting into the chocolate project being created.
- Ice can be added to the water to lower the temperature back to the 65°F to 69°F (18-20˚C) range. However, never allow the ice to come in to contact with the side wall of the chocolate container, or lumps are likely to develop, as areas where ice contacts the container wall are likely to drop below 60°F (15.5˚C), which is the temperature chocolate rapidly starts to solidify.
- Scrape the chocolate container side walls frequently to prevent chocolate from attaching to the wall.
- Remember, as the delta between the chocolate and the water decreases, more time will be required to reduce the temperature of the chocolate.
Components of a Simple Water-Based Heat Sink (Figure 1)
- Chocolate container
- Heat sink bowl
- Heat transfer fluid
Using a Water-Based Heat Sink to Remove Sensible Heat
- Fill container ½ to 2/3 of the way full with water at a temperature between 65°F and 69°F (18-20˚C)
- Place the container of fully melted chocolate into the water
- Monitor the temperature of the chocolate every three to four minutes, and more frequently as the temperature gets closer to the desired seed addition temperature
- Scrape the side wall when monitoring temperatures to prevent chocolate from solidifying on the side walls
- Remove the container as the chocolate temperature approaches the desired temperature. Remember, the temperature is likely to equilibrate higher than the read temperature.
- Reheat or cool until desired seeding temperature is obtained
Dennis Teets has worked in the confectionery 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].