A Fresh Vanilla Pod Has No Smell of Vanilla
A green vanilla bean smells like grass. The flavor is locked inside, waiting on an enzyme to release it.
Pick a vanilla pod off the vine in Madagascar and you would not guess what it is. Green, fleshy, faintly grassy — no smell of vanilla at all. The molecule responsible for the flavor of every ice cream cone, vanillin, is barely present. What the pod is full of is glucovanillin, an odorless sugar-bound version of the same compound. Roughly 11% of the dry weight is glucovanillin; only about 0.2% is free vanillin.
Turning one into the other is a slow, mostly enzymatic affair. The Bourbon method, used in Madagascar, runs five to eight months. Pods are dropped into water at 65 degrees Celsius for about three minutes — enough to kill the cell tissue and break the bonds keeping enzyme and substrate apart. They go straight into wool-lined boxes to sweat. They alternate sun and shade for weeks. They are conditioned in waxed paper for another month, while the chemistry finishes itself in the dark.
What is happening inside the pod is hydrolysis. The plant's own beta-glucosidase, an enzyme that was kept walled off from glucovanillin in the live tissue, is now free to act on it. It clips the glucose group off the molecule and releases vanillin proper, the compound that smells like vanilla. Other reactions — Maillard browning, oxidation — generate two hundred or so additional aromatics that round out the flavor.
A paper by Ruiz-Terán and colleagues in 2001 showed you can shortcut the process with industrial enzymes and pull the vanillin out in eight hours at 70 degrees Celsius, at three times the yield. The cured-pod aroma it produces is thinner. Six months in a wool blanket is doing more than waiting.
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