
The Science of Stone Grinding Cacao
We get a lot of good questions about why we stone grind cacao and how the process works. We typically grind cacao for three to four days to make chocolate, and in this article, we’ll walk you through each step of the process.

After we roast and winnow cacao beans, they look like this. Just cacao "nibs," which are the key ingredient in chocolate. These nibs are ready to be put into our granite stone grinder.
Day One: starting with cacao nibs
We are a bean-to-bar chocolate maker, which means that we start with raw cacao, roast the beans, then grind the beans to make chocolate. The picture above shows what cacao looks like after it’s been roasted and winnowed. These are cacao nibs – what’s inside the outer husk – and they are the starting point for all chocolate.
Our biggest stone grinder can work 50 pounds of chocolate at a time, using two granite grinding wheels that rotate on top of a granite base. These nibs are roughly 50% cocoa butter and 50% cocoa solids. Cocoa butter is what gives chocolate its smooth, liquid texture once fully released and melted, but at the beginning of the process, the nibs are still quite solid. The friction and heat of the grinder release the cocoa butter, gradually transforming the solid nibs into a thick liquid.
But if we add the nibs too quickly, the cocoa butter won’t release fast enough to keep the mixture fluid, causing the grinder to seize up, forcing us to dig out the solidified cocoa mass and start everything over.
For that reason, we load grinders slow and steady while applying a heat gun to help the cocoa butter release from the nibs. We’ve also learned that the ambient temperature of the room makes a big difference in how quickly a stone grinder can be loaded – if the room is cool, the butter won’t release as easily, slowing down the process even more.
On the first day of the grinding process, many of the more acidic compounds within the cacao are being released and going airborne. How this plays out depends a lot on the origin we are working with: our Peru origin is so acidic that it almost burns your eyes to look over the grinder on the first day of grinding. But that is part of the beauty of stone grinding: it allows the cacao to oxidize (becoming less acidic and less bitter) and it also allows many of the more volatile compounds to off-gas while it works.

Cacao working in a grinder. You can still see some granularity in the cacao mass, which means it requires further grinding.
Day Two: SMOOTHING IT OUT
On day two, much of the most volatile acids have left the cacao, and things are starting to look a lot more like silky, smooth liquid chocolate. At this point, our focus shifts to reducing the particle size. And by particle size, we mean the actual size of the cocoa solids that are in the grinder.
For chocolate to feel smooth in the mouth, the particles need to be incredibly fine – around 20 microns or smaller. This is the threshold where most people perceive liquids as "smooth” on the palate, and no longer detect any graininess.
For that reason, when making chocolate, our goal is to grind down the cacao particles until the average particle is 20 microns or smaller. And microns are SMALL … one micron is equal to 1/1000th of a millimeter. To measure that, we use a device called a “micrometer” which is beautifully simple: you put a small dollop of chocolate on the top of the micrometer and then scrape the chocolate down a tapered trench. Along that trench are markings for 50 microns, 40 microns, 30 microns, and so on. Once you can see a good amount of chocolate at or below the 20-micron line, you know that your chocolate is somewhere in the ballpark of 20 microns. For most of our origins, that happens somewhere between day two and day three of the grind.
Day Three: adding sugar

This picture shows silky smooth chocolate in our tempering machine after it has finished stone grinding. Notice how smooth the chocolate now looks compared to the previous photo.
Day three is when we start looking to add sugar to the cacao. Our focus is making two ingredient chocolate, which means that the only two ingredients we use are cacao and organic cane sugar. We choose how much sugar to add depending on what percentage of dark chocolate we want to make. For example, 70% dark chocolate contains 30% sugar, while 80% dark chocolate contains 20%, and so forth.
Like the cocoa solids, the sugar needs time to break down into particles smaller than 20 microns. In our stone grinders, we’ve found that the process takes about 24 hours to complete.
Sugar is also a highly absorbent food item, and that’s why you will hear chocolate makers say that the sugar “locks in the flavor” … in other words, adding sugar to the cacao mass working in the stone grinder will preserve the acids and other more volatile compounds, and will prevent the chocolate from becoming more mellow at that point. For that reason, the timing of adding sugar to a batch of chocolate can be just as important as the amount you add.
Day Four: THE FINISH LINE
Some origins only need three days in the grinder, while others with more acidity or stronger flavor profiles can take four days or more.
By day four, we’re closely monitoring how the flavor is evolving and how the particle size (aka smoothness) is progressing. Once the flavor and the particle size are right where we like them, we pull the chocolate from the grinder and pour it into molds to create “bricks.”
These chocolate bricks are essentially solid blocks of untempered chocolate that we store for later tempering. (The final stage between raw cacao and finished chocolate, tempering is a crucial process that aligns the chocolate's crystal structure, giving it that shiny finish and perfect snap, but that's a whole other story – one that combines science, art, and frankly, luck. We'll dive deeper into the world of tempering in another post!)
And it’s also important to note that you CAN over-grind chocolate — when this happens, the chocolate becomes too oxidized, and too many of the flavor compounds are released into the air, resulting in what some folks call chocolate that is a bit “flat” or “boring.” And we think there' ain’t nothing worse than boring chocolate.
Closing Thoughts
That’s the 10,000-foot overview of why we stone grind cacao to make chocolate. If you have any questions or want to see the process for yourself, we invite you to stop by our chocolate factory and shop located at 30 Shawnee Way Suite in Bozeman, Montana!