Spontaneously fermented. It was slow to start with a 17 day lag phase from racking the juice to when fermentation started, followed by a slow , cool ferment. in Mid December, the ferment got so slugish we put the chiller on at 2.3% residual Sugar. Don't expect a sweet Riesling just because of a little RS. This wine is delicious and very balanced. Tons of quince, key lime, acid and minerality.