Final answer:
The compound missing in Oloroso Sherry but present in Fino Sherry is a yeast called 'flor'. Flor protects Fino Sherry from oxidation during fermentation and aging, while its absence allows Oloroso Sherry to oxidize and develop different characteristics.
Step-by-step explanation:
The chemical that is missing in Oloroso Sherry but is found in Fino Sherry is a compound known as flor. Flor is a layer of yeast that develops on the surface of the wine during fermentation and aging in barrels. This yeast plays a critical role in the production of Fino Sherry by providing a blanket of protection against oxidation, giving Fino Sherry its unique flavor profile. The absence of flor in Oloroso Sherry allows for controlled oxidation, which results in its fuller body and darker color.