Pour all the ingredients (except for the baking soda) into a large, heavy stock pot.
Bring to a simmer.
Once the mixture begins simmering, carefully add the baking soda.
The mixture will foam and rise, so add it slowly while stirring.
When it begins to bubble over, reduce heat.
(Or turn off completely until the bubbles reduce. Then turn back on to low-med heat).
Stir for 45 minutes on medium-low.
Remove some of the foam on top.
It will begin to develop a caramel color.
Stir frequently throughout cooking, making sure to scrape the bottom and sides of the pot.
As the mixture thickens, stir constantly to prevent scorching.
After 55 minutes, check the texture.
The texture will be thick and coat the back of a cooking spoon.
Remember that it will continue to thicken as it cools.
Once this happens, remove from heat.
Let cool for 10 minutes before pouring into an airtight container.