Q. Hi Peter, I usually plant a Nantes-type carrot for their wonderful snappy, fresh taste. I’ve noticed that, year to year, they have varying degrees of sweetness/bitterness to them. Mostly they are as sweet as you’d expect from a Nantes. I’m wondering if there is something I am doing to effect their sweetness/bitterness? I only use an organic type fertilizer worked into the soil at sowing time. Thanks again, Henry Raynor – Puyallup, WA
A. Carrots quality is often based on their sugar content, but as you mention sometimes they are sweet and sometimes bitter. The two key factors in carrot taste are volatile terpenoids and free sugars. Carrots taste bitter when volatile terpenoids are not balanced with sufficient sugar. Much of carrot breeding goes into influencing the genetic part of the equation. So some varieties can be sweeter because of their genes. As you have witnessed even in one variety you can find differences from year to year. Carrots can store their reserve energy in the root system in the form of starch or sugar. Starch is formed when two or more sugar molecules are combined. When the starch molecule then can be split again to release the sugar. Carrots growing in temperatures above 70 tend to form shorter, thicker roots and have less available sugar. This is because respiration is higher in warm weather so the carrot tops are using up the free sugar so it does not accumulate. In cool weather respiration is lower and more free sugar remains in the root. Optimal temperatures are between 60 and 70 degrees for sweetness. Carrots are biennial and after the first year they change gears from starch accumulation and initiate the flower bud, which also increases the sugar levels as starches are converted to sugars but are not yet used. Cold weather is the signal to the plant between the first and second year of growth. This is why carrots harvested in late fall and early winter (like for Thanksgiving or Christmas) can be sweet. Carrots can also grow sweeter in cold storage. I have also seen research that shows high nitrogen and potassium levels in the soil can also reduce the sugar in carrots. So as you can see there are many factors that can influence the taste of your carrots as the genes of the carrot interact with the environment.