There are a few potential reasons why the insides of brussels sprouts may turn brown:
Overcooking
The most common reason brussels sprout interiors turn brown is overcooking. Brussels sprouts contain chlorophyll, the green pigment in plants. When overcooked, this chlorophyll breaks down and turns brown. To avoid this, cook brussels sprouts just until tender-crisp – about 5 minutes for halved sprouts or 10 minutes for whole. Brussels sprouts that are bright green on the outside but brown in the middle have been overcooked.
Age/Storage
As brussels sprouts age, the inner leaves slowly start to yellow and turn brown. Older sprouts or sprouts that have been stored too long will often have brownish interiors. For the freshest sprouts with bright green interiors, look for sprouts that feel firm and heavy for their size and have tight, bright green outer leaves. Avoid sprouts with yellowing outer leaves. Store fresh brussels sprouts in a perforated plastic bag in the refrigerator for 3-5 days.
Freezer Burn
Brussels sprouts that have been poorly blanched or improperly frozen can develop freezer burn, which causes the insides to turn brown. To freeze brussels sprouts properly:
- Trim and clean sprouts
- Blanch in boiling water for 3-4 minutes
- Immediately transfer to ice water to stop cooking
- Pat dry and freeze in a single layer on a tray before transferring to a freezer bag
Freezer burned sprouts may still be safe to eat but will likely be lower in quality with a soft, mushy texture.
Diseases/Pests
Certain diseases and pests can cause the insides of brussels sprouts to turn brown:
- Black rot – Bacterial disease that causes dark brown or black spots inside leaves
- Downy mildew – Fungal disease that turns internal leaves yellow then brown
- Caterpillars – Chewing insects that bore into heads and leave behind brown frass (insect waste)
Prevent disease and pests by purchasing sprouts from reputable growers, avoiding sprouts with visible signs of damage, and consuming sprouts soon after purchase.
Nutrient Deficiencies
Lack of certain nutrients when growing can also cause inner leaves to yellow or brown:
| Nutrient | Deficiency Signs |
|---|---|
| Nitrogen | Uniform yellowing of inner leaves |
| Boron | Brown heart in sprout head |
| Calcium | Tip burn on inner leaves |
Purchase sprouts from reputable growers to ensure proper nutrition during growth.
Conclusion
Brown insides in brussels sprouts are most often caused by overcooking, age/poor storage, or improper freezing. Diseases, pests, and nutrient deficiencies in growth can also sometimes be factors. To avoid brown interiors, purchase fresh, undamaged sprouts from reputable sources and take care to not overcook them. Look for sprouts that feel firm and heavy and have tight, bright green outer leaves. Store sprouts properly in the refrigerator and avoid freezing them for best quality.