The Gist
Butter, cream, or butterscotch on a white wine almost always means malolactic fermentation happened — a winemaking choice that softens acid and releases a buttery compound called diacetyl. Among the major exam grapes, only Chardonnay routinely undergoes it. Buttery white = Chardonnay until proven otherwise.
Mechanism
Malolactic fermentation (MLF) transforms sharp malic acid into softer lactic acid — reducing perceived acidity and producing diacetyl, the compound responsible for butter and cream aromas. MLF is nearly universal in red wines but is a deliberate winemaker choice for whites. In Chardonnay, full MLF + barrel fermentation + lees contact creates the classic "butter bomb" style.
Butter/cream/butterscotch on a white wine = MLF = Chardonnay in most the exam contexts. No other testable white commonly undergoes full MLF. Diacetyl eliminates Riesling, Sauvignon Blanc, Chenin Blanc, Viognier, and Grüner Veltliner simultaneously.
Deeper mechanism
Lees contact (sur lies aging) produces complementary aromas of yeast, brioche, and toast — often layered with diacetyl in oaked Chardonnay. The combination of butter + hazelnut + toast is almost always Chardonnay. Pessac-Léognan Sauvignon Blanc can be heavily oaked and structured — but SB-based Bordeaux Blanc does not undergo MLF, so butter is absent. Citrus character and a faint herbaceous note through the oak remain the tell.
Confusion analysis
Oaked Chardonnay vs. Oaked Pessac-Léognan SB
Both heavily oaked French whites. MLF butter = Chardonnay. No butter, citrus/herb persists through oak = Pessac SB. The presence or absence of diacetyl is the single decision point.
Chardonnay (oaked) vs. Viognier (oaked)
Both full-bodied oaked whites. Viognier: florals (apricot, violet) survive through oak. Chardonnay: no florals, butter/cream instead. The floral axis separates them.
Related varietals
This concept comes up when tasting: Chardonnay