Cut or scrape off zest, yellow part of rind. Then peel grapefruit and discard pith or white part. Separate grapefruit sections and cut each section into several pieces. Combine the rest of the ingredients. Cover.
Leave to infuse for several weeks. Strain and let the liqueur clear for a week to 10 days. Carefully pour off the clear liqueur. If desired, a small amount of yellow food dye may be added for a stronger yellow color.