Pet Nat is short for pétillant naturel. In its purest form, as this is, Pet Nat has an ingredient list limited to just grapes (with no Sulphur added). After spontaneous fermentation begins but before it is complete, the wine is bottled. Fermentation continues under a closed cap creating those delicious bubbles.
This 100% Chardonnay comes from the Conzleman Vineyard in Anderson Valley planted to the Wente clone in 1981.