When apples leave cold storage, they keep ripening — and their sugar levels keep climbing. A refractometer measures this increase in degrees Brix, giving a precise look at how sweetness builds over time. Not every variety follows the same curve, though. Red Delicious, Golden Delicious, and Granny Smith each gain sugar at different rates, so the variety you pull from the refrigerator determines how quickly that post-storage sweetness arrives.

Place three drops of freshly juiced apple on a refractometer and it measures dissolved sugar in degrees Brix — a standard unit for sugar concentration. As apples sit on the counter after leaving cold storage, their sugar levels shift. By recording Brix readings for each variety twice a week over several weeks, you build a sugar curve for granny smith, golden delicious, and red delicious apples. That means you can compare not just how sweet each variety is, but how fast it changes once it comes out of the refrigerator.