TAPPING THE WALNUT TREES
We like to think of the CVI FoodLab as a think-tank of ideas. Some of those ideas are good, some are not so good, some are just really weird. But we are always thinking, testing, experimenting, and always willing to work with the results.
For the last few months we have been focused on how we can utilize our natural resources around the Institute to come up with something unique and delicious. So, armed with a hand drill, spikes, buckets, butcher’s twine, and a hammer we set out to start tapping the Black Walnut Trees scattered around the woods on our grounds in search of sap.
According to the Carry Institute of Natural Science, all trees produce stockpiles of sugar during their growing season to be used in Spring to regrow their leaves. Some of those sugars are stored in the tree’s trunk in what are called rays.
If you look at the stump of a tree, you will see the unmistakable multicolored rings. Perpendicular to the rings, the rays, or sugar cells, run from the center of the tree to the bark. These rays consist of living cells that hold sugars that trees use for building new cells or for repairing damage from a woodpecker or other pest. These rays are also the source of the sugar for making syrup.
The cell configuration in sugar maples is just right to allow sap to flow in the Spring. However, not all species of trees are so easy to give up the goods. For a sugar maple, the ratio of sap to syrup is 40:1, which by way of quick math means that it would take 10 gallons of sap to make one quart of syrup! Now take a Birch tree, for example, and the ratio climbs to 80:1! Our Black Walnut trees fall in at about 67:1.
Once the tree is tapped, physics and nature are what drain the sap from the tree. Nights with temps below freezing followed by days with temperatures in the 40s and 50s are what make the sap flow. The freeze-thaw cycle causes changes in atmospheric pressure, which forces the sap to move. At night, when the temperature cools, gasses dissolve into the sap fluid, causing a decrease in pressure in those cells. The fluid in the wood freezes, compressing the gases in ice. As the temperature increases the next day, the ice melts, the sap beings to warm up, and the gases expand, forcing the sap to run out of the tree and into the collecting bucket. If the temperatures remain below freezing during the day or well above freezing at night, those pressure differences will not occur and the sap will not flow. As you can see, there is obviously a window that needs to be met for maximum sap retrieval. We may have missed it by a few weeks this year, but we will know for next year exactly when to get started. Even though we got into the trees a bit late, we are still collecting about 6 quarts a day! The sap is thin and watery and tastes sweet with a hint of walnut skin in the finish.
Once the sap is collected it is boiled down. This is where chemistry is important. As the sap boils, pure water evaporates and the sucrose concentrates. This produces a lot of steam. During the boiling foam will rise to the surface every few minutes and must be skimmed off. This foam is the product of a chemical reaction that occurs as the sap heats, it’s an impurity that is harmless but doesn’t taste so great. It is called niter, and will make your finished product gritty and unpleasant. It is mostly made of potassium, calcium, silica, magnesium, sodium, and other minerals found in sap. The proper temperature should be about 219 degrees F and 66 brix on a refractometer.
Once the skimming and boiling is done, usually after about three hours, you are left with a rich brown and delicious syrup, somewhere in color between honey and maple syrup, with a slightly nutty flavor and a natural sweetness.
Overall we collected five gallons of sap from the walnut trees around the CVI, and cooked it over open coals to boil the sap down. What we were left with was slightly more than a pint of incredible walnut syrup! The syrup is dark in color, almost like a thin molasses. The flavor is sweet and nutty with hints of smoke from the fire we built to boil it down.
Even thought we got a late start in tapping the trees, this project was an enormous success for us. This syrup is completely unique and has left us wondering what other trees we need to tap next season. Rest assured you will see this luxuriously nutty treat on dishes at the CVI this spring, summer, fall!
—Ülfet Özyabasligil Ralph