Bolting or flowering of most brassicas will affect the taste. They do become more bitter. It's also not unusual for them to develop an unpleasant aroma as well. Ornamental cabbages and kale that folks use for winter plantings typically reek at this time of year!!

Concur. Brassicas develop strong flavors and smell when bolting. Not poisonous but unpleasant..

For years I grew Winterbor Kale--gets quite tall in the fall. As the climate warmed, it overwintered and the spring flush of new growth from the nodes where the old leaves met the stem were absolutely delicious sprouts for salads or stir fry. The tiny heads and the entire sprout were the earliest treat of spring.

Thank you all for your responses! @laceyvail 6A, WV I think - judging from the name of the kale you grew (Winterbor) - the variety was grown specifically for winter growth, and perhaps the genes to make it taste unpleasant were selected out. Thus your tasty treat. The plants I grew were for a summer crop that I just left in the garden to overwinter and bolt.