Petaluma Gap AVA anniversary tasting

Two years on from gaining its AVA status – uniquely defined by the wind – Jeff Cox assesses the quality of several cool-climate Chardonnays and Pinot Noirs

Held on 8 January – two years to the day the AVA was approved by the US federal government, the Petaluma Gap Winegrowers’ Alliance set up a tasting in Petaluma city.

Eighteen of the 35 member wineries were represented, some having wineries within the AVA but most making wines using Petaluma Gap fruit at wineries elsewhere in Sonoma County.

‘Petaluma Gap is the only AVA in the country defined by the wind,’ said Cheryl Quist, executive director of the Alliance, whose motto is ‘Wind into Wine’.

To set the appellation boundaries, machines that measure wind speed were set up around the southern end of the large Sonoma Coast AVA. Wherever wind speed averaged about 13km/h or more, that region defined the Petaluma Gap sub-appellation that covers 82,000ha.

Of that, more than 1,620ha are under vine: 75% Pinot Noir and 13% Chardonnay, some Syrah and a smattering of other varieties.

The wind measurement is important because when wind speed reaches 13km/h, vines close the pores, called stomata, on their leaves. These regulate the exchange of water vapour, oxygen, and carbon dioxide into and out of the leaves.

When the stomata close, leaf metabolism and the transpiration of water slow or stop, delaying fruit ripening and increasing hang time.

Grapes in the Petaluma Gap get a double whammy of grape ripening suppression because the afternoon winds off the cold ocean flow over the AVA like natural air conditioning, and then that eastward rush of cold air brings nightly fog with it, further reducing temperatures.

As Mark Twain wrote: ‘The coldest winter I ever spent was one summer in San Francisco.’ The city’s Golden Gate Bridge is just 48km south of Petaluma and is another break in the hills where cold ocean air rushes in.

Burgundian varieties

The northern Marin County and southern Sonoma County sites influenced by the cool Petaluma Gap climate produce fruit that struggles – and that’s a good thing.

Like similarly cool-climate Burgundy, the climate favour Pinot Noir and Chardonnay. The berries are smaller, with thicker skins (and thus more stuffing on the palate) and can have a greater acid-to-sugar ratio than grapes grown in warmer, protected inland valleys.

More acid means the wines, especially the whites, are super thirst quenching and all the wines, red and white, have a greater potential for longer ageing.

The tasting revealed a bell-shaped curve of quality – but picture a bell lying on its side.

In other words, there were some unpleasant wines, a bulk of good to very good wines, and then the bell flared out at the upper end of quality to reveal wines of true greatness.

Instead of the blueberry and cola notes found in Russian River Pinot Noirs, here you find intense strawberry flavours – almost wild strawberries – and in the best wines a perfect balance of elegant structure, sweet fruit and tangy acidity.

The best of the Chardonnays were just as good. These are more focused on an apple character, with their malic acidity and rose-family perfumes, than with the lemony flavours so associated with Carneros.

Among the few other varietals on show, Cline Cellars’ 2018 Estate Viognier ($20) was delicious. The bright, striking nose of white flowers and apricot leapt out of the glass, leading to long, lush fumey (14.5%abv) flavours of pineapple and lime.