Once this feature is enabled, when wines go from a positive inventory to less than or equal to 0, the wine is flagged. With the report, RB - OUTS (Inventory Not Available) Report, you can see which wines had their inventory go negative for a specific date range (Dates are based on physical order placement date.)

NOTE: Enabling this feature only tracks orders placed going forward. Historical/existing orders are not captured.
Admins can enable this feature by editing their admin panel settings (My Account) and checking the box for 

Track Negative Inventory / Order Requests?.