Terroir is a game about winemaking. The game has a hex-based map which fades off into nothing, but slowly grows as the player increases the size of their estate.
Players start the game with a mansion, a lake, and a vineyard. The vineyards can cultivate different kinds of grapes, which each have their own properties. Cultivation itself is a real-time process that involves trimming the vines so that the grapes get a certain level of ripeness. Grapes that are over- or under-ripened will have lower base quality levels than grapes that are cultivated properly.
Once the grapes have been harvested, the player must then decide upon their wine-making strategy for each type of grape that was harvested. Each grape harvest has 4 characteristics - Acidity, Sweetness, Tannins and Body and each type of wine has its rating improved by having some of those characteristics higher than others. For example, Chardonnay does better with higher Acidity and lower Sweetness.
The wine is rated by wine critics, with 5 stars being the highest rating, and the critics rating sets the price the wine can be sold for. Additionally, the more prestigious the player's vineyard becomes, the more prestigious the wine critics the player can invite to the tasting. Having a 5-star wine from more prestigious critics means it can sell for more, and have a larger increase of the player's prestige.
There are various additional processing methods to unlock as the player's prestige increases. Also, the player can increase the size of their estate by buying more land, and therefore planting more grapes.
Much of what makes the wines rate highly seems to be relatively similar to what people would look for in the real version of the wines. Therefore oenophiles may have an advantage in how quickly they're able to figure out what will give them highly rated wines.