You can substitute agave syrup with maple syrup or another sweetener. For a completely smooth consistency, strain the syrup through a fine-mesh sieve. It keeps for a few days in a sealed container in the refrigerator — this syrup is blended cold without a cooking step, so the sugar does not preserve it as long as a cooked syrup.
The Vitamix breaks open the zest cells of the lime more finely than hand-stirring or a standard blender — this releases the essential oils from the zest completely into the syrup without requiring you to zest the peel separately. Important: blend only briefly (a few seconds or pulse bursts) to avoid releasing bitter compounds from the white pith.
Blend only briefly — a few seconds of continuous run or 3–4 short pulse bursts are enough to combine the juice and zest. A long continuous run releases bitter compounds (limonin) from the pith, causing the syrup to darken and turn bitter. If you want to be safe, strain the finished syrup through a fine-mesh sieve.