It's rarely this easy to tell whether a wine was made from organic grapes.

I’ve received a deluge of emails from readers during the last week in response to an article I wrote about Roundup, the controversial herbicide, and its use in California vineyards.

Many of you wrote to me with the same question: When I’m buying wine, how can I tell whether its grapes were farmed with Roundup? 

Basically, if the wine was made from organically, biodynamically or regeneratively farmed grapes, then it wasn’t farmed with Roundup. Unfortunately, however, it can sometimes be more difficult than it ought to be to find that information.

Some wine bottles make it easy for you, by carrying a little seal from one of the certification programs. Look for the following logos: USDA Organic, CCOF Organic, Demeter (a.k.a. biodynamic), Regenerative Organic Certified, Agriculture Biologique or Biodyvin (the latter two for European wines).

But, confusingly, not all organically farmed grapes will end up in a bottle with an organic logo. That might be because a farmer farms organically but has chosen not to obtain a formal certification, for one reason or another. Since these certifications take several years to obtain, a farmer might have to wait a few years after starting to farm organically before their wines can reflect it. 

It’s also possible for a wine’s grapes to be organic but the wine itself to not be organic. For example, the U.S. Dept. of Agriculture stipulates that its organic-certified wine must not have more than 100 parts per million sulfur dioxide — a preservative — added to it. So some perfectly organic grapes might end up in a wine that doesn’t meet this particular qualification. Such a wine could still say “made with organic grapes” on its back label without carrying an organic-wine logo. Still, in this case, the grapes will not have been farmed with Roundup.

This all makes for a lot of squinting while perusing bottles in the wine shop, I know. Like I said, it ought to be easier. 

If there’s an easy online search tool for finding wines that meet these specifications, I’m not aware of it. The USDA’s Organic Integrity Database, which allows you to search for all U.S. agricultural producers that carry a variety of organic certifications, is kind of a nightmare from a user-experience perspective. Demeter, the biodynamic certifier, has an online directory (not specific to wine) that is a little better.

The best resource I can recommend is the Slow Wine Guide, an annual publication that vets wineries for a range of ecological criteria. The guide recommends wineries that do not use chemically synthesized fertilizers (like Roundup), and also checks for things like water use, sustainably constructed buildings and intervention during the winemaking process. (The guide, for instance, does not include wineries that use oak chips, a shortcut that is sometimes used instead of aging a wine in an expensive oak barrel.) It’s a physical, printed publication, and costs $25.

I was heartened to see that so many of you are interested in becoming more conscientious wine buyers. But I also want to emphasize that Roundup is not the only thing that matters — far from it. As many industry players told me during my recent reporting, it’s the thing that everyone asks about, the farming chemical everyone in America has heard of. That’s frustrating to many farmers, vintners and environmental advocates, who hope that wine drinkers will start asking other questions too. How does the business treat its workers? Is it thinking about how it might be able to help mitigate some effects of climate change?

Ultimately, the only foolproof way to buy products you feel good about is the hardest way: to have an old-fashioned conversation with the people who made it. The good news is that this is easier at wineries, which tend to operate tasting rooms, than at many other types of businesses. So the next time you’re visiting one, take advantage. Have a conversation.

Senior wine critic Esther Mobley joined The Chronicle in 2015 to cover California wine, beer and spirits. Previously she was an assistant editor at Wine Spectator magazine in New York, and has worked harvests at wineries in Napa Valley and Argentina.