Why avoid raw kale stems?
Written by
Tina Carter
Reviewed by
Prof. Martin Thorne, Ph.D.Stems of raw kale can be a digestive issue. The tough cellular structure contains cellulose fibers that resist breakdown and may result in bloating and other digestive disorders. Cooking alters the fibers, making the stems edible and nutritious. Being familiar with the proper way to prepare them will let you enjoy the whole plant safely.
Digestive Issues
- Cellulose fibers remain undigested in human systems
- May cause intestinal gas and cramping
- Fiber content triples that of leaves increasing bulk
Bitter Compounds
- Concentrate glucosinolates 3x more than leaves
- Develop tannins during growth increasing astringency
- Accumulate alkaloids affecting flavor balance
Contaminant Risks
- Pesticide residues concentrate in vascular tissues
- May harbor soil pathogens from splash contamination
- Accumulate heavy metals more than leafy portions
Cooking methods. These increase stem digestibility. Heat above about 140°F (60°C) ruptures cellulose matrices. I always slice stems thinly before sautéing so that they cook evenly throughout. The cooking process releases (i.e., preserves) all nutrients and sufficiently destroys any bacteria that may not be removed through raw consumption.
Decreasing bitternes: A method is used in Asia to decrease the amount of bitter compounds by blanching the stems for 90 seconds in boiling salted water and then plunging them into an ice bath. Glucosinolates are reduced by this method, but the stems remain palatable and possess significant nutritional value together with a low-density caloric system. Marinades in acidic (e.g. citrus juices) solutions reduce tannins.
Why Avoid Raw Kale Stems? The stems of raw kale can be hard to digest due to the presence of cellulose fibers (which can cause stomach pain) and concentrated substances that give the vegetable strong, bitter flavors. The stems of kale can also contain pesticide residues. Cooking tends to destroy these compounds.
Read the full article: How to Grow Kale: Ultimate Guide for Home Gardeners
