Test pH with red cabbage water indicator

Chop red cabbage and boil in distilled water (2 cups each) for 10 minutes. Strain and cool the purple liquid. Add 2 teaspoons of garden soil to a jar with a few inches of cabbage water, stir, and wait 30 minutes. The color tells you the pH range: red/pink means strongly acidic, purple means mildly acidic to neutral, blue-green means mildly alkaline, green/yellow means strongly alkaline.

Why It Works

Red cabbage contains anthocyanin, a natural pigment that changes color across the pH spectrum. This makes it a legitimate pH indicator, used in chemistry education worldwide. Georgia Tech's chemistry department publishes this as a standard demonstration. It provides more nuance than the vinegar/baking soda test because the color gradient maps to a range rather than a binary fizz/no-fizz.

Tips

• You must use distilled water — tap water or well water has its own pH and will skew results
• Still imprecise compared to a pH meter or lab test — cannot distinguish 6.2 from 6.8
• Good educational activity, especially with kids
• Cost: one red cabbage (~$2-3) plus distilled water (~$1) provides enough indicator for many tests