Final answer:
The oldest wine level in a solera system is called the base or solera wine, stored in the solera tier. It is blended with new wine to create a unique flavor profile.
Step-by-step explanation:
In a solera system, the oldest wine level is known as the "base" or "solera" wine. This wine is stored in the bottom row of barrels, known as the solera tier. As new wine is added to the system, it is blended with the wine in the solera tier, which contributes to its distinct flavor profile. The base wine can be several years or even decades old, depending on the solera system.