Why does my kale taste bitter?

The presence of bitterness in kale most often is a sign of stress or simply that it's reaching symbolic maturity. I experienced strong bitter flavors in my first crop until I started to recognize patterns: when the kale leaves matured too much or when the air temperatures got hotter in the summer. In response to stress, kale creates chlorogenic acid, which increases flavor intensity and bitterness levels. Cooler air temperatures and careful harvests can play a huge role in bitter flavors and enhance enjoyment.

Frost changes the taste of kale by converting the starches to sugars. I try to leave fall crops unharvested until the temperatures drop below 28°F (-2°C). After a frost, the kale leaves taste 40% sweeter than before. In frost-free zones, harvest the leaves and freeze them for twelve hours for the same effect. This works great when harvesting a big batch for a smoothie.

The nutrition of soil is largely unseen. Fertilizers high in nitrogen tend to increase leaf size but also increase bitterness when eaten. I apply 2 cups of wood ash per 10 sq ft of soil to increase the potassium level, this creates a balance of flavors. You should test your soil every year - pH levels above 6.5 will lock out magnesium levels, which is another bittering component.

Cooking diminishes bitterness. Blanching leaves for 90 seconds can reduce the sharper plant compounds by about 70%. For raw salad, sometimes it works well to massage the leaves with olive oil, making it easier to break down the tough fibers. Both of my kids will gobble up massaged kale salads but won't eat the leaves in their unprocessed form. They legitimately care about texture as much as taste.

Read the full article: How to Grow Kale: Complete Planting and Harvesting Guide