Zinfandel: how one black grape becomes red, sweet pink or dry rosé

One black grape, two separate decisions

Zinfandel is a black grape. Its red pigments, the anthocyanins, are held in the skins, and tannin comes from the skins and seeds. Both pass into the wine only while the juice stays in contact with these solids: the length of skin contact, the temperature and the handling of the cap of skins are among the factors that affect how much colour and tannin a wine takes up (review by Sacchi and colleagues, 2005).

That is how one variety gives three very different wines. White Zinfandel is a blush wine whose juice is separated from the skins after crushing and fermented like a white wine, with residual sugar giving a light sweetness. Zinfandel rosé has only a very short skin contact and is typically fermented dry. Red Zinfandel ferments with its skins.

Keep the two controls apart. Skin contact explains colour and tannin. How far the alcoholic fermentation runs explains how much sugar stays in the wine and how much alcohol is formed. A pale wine can be sweet or dry, and a deep colour tells you nothing about sweetness until you taste.

From Dalmatia to California: one grape, several names

Zinfandel’s American history begins in the 1820s, when George Gibbs, a nursery owner on Long Island, New York, imported unnamed cuttings from the imperial collection at Schönbrunn in Vienna (ZAP, the Zinfandel Advocates & Producers association). Frederick Macondray, a sea captain and horticulturist who had grown the vine in Boston, is credited with bringing some of the first cuttings to California in the early 1850s.

Where the grape came from before Vienna was settled by DNA. In December 2001, Carole Meredith’s laboratory at the University of California, Davis, working with Ivan Pejić and Edi Maletić of the University of Zagreb, confirmed that Zinfandel and Crljenak Kaštelanski, a grape from the Dalmatian coast of Croatia, are the same variety. Italy’s Primitivo has the same DNA profile.

A 2011 study matched Zinfandel’s DNA profile to a herbarium specimen, about 90 years old, of a Croatian grape called Tribidrag. Read together with historical documents, the authors take this as evidence that the variety was grown in Croatia under that name from the beginning of the fifteenth century. The names change from country to country; the grape is one.

Uneven ripening makes the harvest decision difficult

Zinfandel ripens unevenly within the bunch: one cluster can hold slightly under-ripe berries, perfectly ripe ones and berries verging on dehydrated, or raisined. A single average sugar reading can hide these differences.

Each fraction contributes something different. The less-ripe berries bring bright acidity, the ripe ones the main fruit flavours, and the withered ones concentration and depth.

Growers carefully monitor hang time, the time the grapes stay on the vine before harvest, to keep the balance between acid, tannin and sugar. That balance carries into the cellar: the more sugar the grapes hold at harvest, the more alcohol a complete fermentation can produce.

Climate, training and old vines

Zinfandel needs a long growing season in a region that is warm but not excessively hot. Its clusters are tight and its skins thin, so some bunch rot is to be expected.

Traditionally the vines are head-trained, standing free without a trellis, and ideally dry-farmed or only minimally irrigated. This holds back the variety’s tendency to over-produce while giving the tight clusters sunlight and airflow.

Old vines are part of the variety’s identity in California. Most of Lodi’s old-vine Zinfandel is still found on the deep Tokay series fine sandy loam of the Mokelumne River sub-appellation. The Rous Vineyard there, head-trained Zinfandel planted in 1909 on St. George rootstock, supplies all the fruit for Ironstone’s 2022 Rous Ancient Vine Zinfandel. Old vines are still Zinfandel rather than a separate variety, and age alone does not guarantee quality.

Red Zinfandel: ripe grapes, skins, extraction and oak

For a red, the crushed grapes ferment with their skins. A higher fermentation temperature and a longer maceration increase the colour and tannin extracted, while the effect of how the cap is mixed varies with the grape variety. More seed tannin is drawn out as maceration lengthens and alcohol rises.

Ripe, sugar-rich fruit fermented to dryness gives a high-alcohol, full-bodied wine. Ironstone’s 2022 Rous Ancient Vine Zinfandel has 14.5% alcohol and 3.40 g/L of residual sugar. EU rules allow a still wine with no more than 4 g/L of sugar to be labelled dry, so by that measure the wine is strong, yet dry. Ripe or jammy aromas therefore do not prove that sugar remains; judge sweetness on the palate, separately from fruit character.

Oak is a choice, not a requirement. New barrels release more oak compounds, such as vanillin and wood tannins, than barrels that have already been used several times, and the slow entry of oxygen through the wood gradually changes colour and tannin (review by Garde-Cerdán and Ancín-Azpilicueta, 2006). The Rous 2022 spent 24 months in small French and American oak barrels.

White Zinfandel: a pale colour and an unfinished fermentation

For White Zinfandel the juice is separated from the skins after crushing and fermented like a white wine, so it takes up little colour or tannin. Fermentation ends while some sugar remains, which gives a light sweetness and less alcohol than the same juice would have given if fermented dry.

The style began by accident at Sutter Home in the Napa Valley. In 1972 Bob Trinchero drew juice off vats of Zinfandel from the Deaver Vineyard in Amador County to give the red more colour and tannin, and fermented the drawn-off juice into a dry, pale wine. He wanted to call it Oeil de Perdrix, but the federal label authority would not accept the French name, so White Zinfandel was added to the label. In 1975 that wine’s fermentation stuck before all the sugar was used; the pink, sweeter result became the style now known as White Zinfandel.

Any wine that keeps sugar can start fermenting again in the bottle. Stabilising such wines calls for sterile membrane filtration and, while such wines are stored, a cold temperature and enough free sulfur dioxide. Potassium sorbate can help, but only together with proper free sulfur dioxide, and it does not guarantee stability.

The style also mattered to vineyards. In the 1980s and 1990s Zinfandel was used mainly for White Zinfandel, and the craze helped preserve Lodi’s existing plantings, many of them 50 to as much as 100 years old, that growers might otherwise have replaced with Chardonnay or Merlot.

Dry rosé and other fermentation endpoints

Zinfandel rosé is pink too, but it is typically fermented dry. The juice may be bled off after a very short skin contact, which gives a deeper rosé colour, and the wine is light, spicy and berry-flavoured. Same variety, similar colour, a different endpoint.

Dryness does not mean low alcohol. The more of a given juice’s sugar is fermented, the more alcohol forms, so how strong a dry rosé ends up depends on the sugar it started with. Colour indicates neither.

Two further endpoints follow the same logic. Late Harvest Zinfandel is, in most cases, a dessert wine from extremely ripe grapes, often with a noticeable 1–3% residual sugar and with alcohol typically over 15.5%: sweet and strong at once. For Port-style Zinfandel, grape spirit is added during fermentation to stop it before all the sugar has become alcohol.

In the glass, assess sweetness, acidity, alcohol and tannin one at a time, and only then connect them to the decisions above.

Practice question 1: compare red and White Zinfandel

These practice questions and answers were written for this article; they are not questions or answers from any examination body.

Question: Explain why a red Zinfandel and a typical White Zinfandel, made from the same variety, differ in colour, tannin, sweetness and alcohol.

Model answer: Zinfandel is a black grape whose pigments sit in the skins. For a red, the juice ferments with the skins, and the length of contact and the temperature, along with how the cap is managed, affect how much colour and tannin are extracted. Ripe, sugar-rich fruit fermented to dryness gives plenty of alcohol and body; Ironstone’s 2022 Rous Ancient Vine Zinfandel, for example, is listed at 14.5% alcohol with 3.40 g/L of residual sugar. For a typical White Zinfandel the juice is separated from the skins after crushing, so little colour and tannin are extracted, and fermentation ends with sugar unfermented, which gives a light sweetness and less alcohol than the same juice would give if fermented dry. Skin contact therefore explains the difference in colour and tannin; sugar at harvest and the fermentation endpoint explain the difference in alcohol and sweetness.

Mark scheme (self-check, 10 points): pigments located in the skins (1); length of contact, temperature and cap management linked to the extraction of colour and tannin (3); harvest sugar and complete fermentation linked to alcohol and body (2); separation from the skins linked to the pale colour and low tannin of White Zinfandel (2); residual sugar from an incomplete fermentation linked to sweetness and lower alcohol (2).

Practice question 2: why pale pink does not mean sweet

Question: White Zinfandel and dry Zinfandel rosé can both be pink. Explain why the first is usually sweet and the second dry, and what the sweet style meant for California’s old vineyards.

Model answer: In both wines the contact between juice and skins is limited, so little colour and tannin are extracted; the rosé has only a very short skin contact, after which the juice may be bled off, giving it a deeper colour. The difference in sweetness comes from the fermentation endpoint: White Zinfandel keeps residual sugar, whereas the rosé is typically fermented dry. A wine that keeps sugar can referment in the bottle, so it needs microbial stabilisation, for example sterile filtration, cool storage and sulfur dioxide. Colour therefore does not measure sweetness. Historically, the sweet style began with a stuck fermentation at Sutter Home in 1975. In the 1980s and 1990s, demand for White Zinfandel helped keep Lodi’s old Zinfandel plantings, many of them 50 to 100 years old, from being replaced by Chardonnay or Merlot.

Mark scheme (self-check, 10 points): limited skin contact linked to pale colour and low tannin in both wines (2); residual sugar in White Zinfandel and dry fermentation of the rosé (3); colour is not a measure of sweetness (1); stabilisation of wines with residual sugar (2); White Zinfandel demand linked to the survival of old vineyards, with the period (2).