Rioja's second fermentation. Bacteria, barrels and wines built to last.

A region built for aging

Jamie starts in an old Tempranillo bush vineyard in Rioja, Spain's most prestigious region, with around 65,000 hectares of vines, roughly the size of Burgundy and Champagne combined. Grapes, he points out, come with everything needed for wine: sugar, acidity and the yeasts and bacteria that do the work.

It was only in the 1860s, Jamie explains, that people understood yeasts were behind fermentation, and the first malolactic bacteria were not isolated until the 1950s. That history makes the second fermentation feel a little mysterious, even to many wine lovers, and it is exactly what this episode sets out to unpick on camera.

He also tells the story of how Rioja changed in the late 19th century. When phylloxera hit Bordeaux, French winemakers came south and brought small oak barrels with them. Today the region holds more than a million barrels and classifies its wines by how long they spend in barrel and bottle.

Meet the microbiologist

Jamie's guide is Dr. Rubén Martínez, who holds a PhD in wine microbiology. He explains that after yeasts turn sugar into alcohol, lactic acid bacteria living on the grape skins can turn sharp, apple-like malic acid into softer lactic acid, the kind found in milk and yogurt. The wine becomes less acidic and can pick up buttery, yogurt-like aromas.

Rubén stresses a less obvious benefit: the bacteria also consume other nutrients, such as citric acid and leftover sugars, so other microbes cannot grow later. That is one reason the process is linked to stability. The catch is timing. Until it happens, often in spring as cellars warm up, the wine cannot be protected with sulfur dioxide, which makes it a critical stage.

Inside 200 Monges

At the 200 Monges winery, owner and winemaker Ángel explains a deliberately traditional approach. Tempranillo goes through full malolactic fermentation, while Garnacha and Graciano may have full, partial or none, depending on what will keep the blend fresh for long aging. To hold back the bacteria, he can use granite or concrete vessels.

Jamie tastes fresh Tempranillo Blanco must, which will not go through malolactic because the team wants to keep its freshness. Later, the winery's Sylvia shows the underground cellar of old bottles that her father and grandfather built in 1992. The current Gran Reserva release is 2007, with two years in barrel and nine in bottle before sale.

Experiments in the lab

The episode has plenty of hands-on science. A barrel sample goes into an automatic analyzer that measures malic and lactic acid to check whether the second fermentation has happened yet. Rubén explains that winemakers who want to avoid it simply chill the wine or add sulfites, because these bacteria are fussy. Jamie calls them prima donnas.

In a sterile setup, Rubén spreads a single drop of wine on an agar plate to grow colonies of lactic acid bacteria, and shows a plate that has grown for five days. It is a rare chance to see the microbes behind a process most wine lovers only read about on back labels.

Side by side in the glass

To make the science tangible, Jamie and Rubén taste a wine that has not been through malolactic fermentation next to one that has, and Jamie describes the differences in acidity, harmony and flow. Then comes the 2007 Gran Reserva, a 17-year-old wine that shows what Rioja's patient approach can deliver.

So is malolactic fermentation truly necessary for wines that age? Watch the episode to see the evidence and hear Jamie's conclusion.