I have just purchased California grapes (white: Chenin Blanc, Sauvignon Blanc, Riesling and red: Sangiovese and Cabernet Sauvignon). The pH for those is between 3.7 to 3.9 and TA is 3 to 4. I learned that pH for whites should be around 3.3 and reds around 3.5. Should I try to lower pH? When during the winemaking process and what method should I use to do this?
Your pH’s do seem a bit high. I agree, for California grapes, I like to see whites in the 3.30–3.45 range and reds in the 3.45–3.65 range when picked. However, many of our winemaking friends live in colder climates and/or make wine styles where they may want to maintain more acidity, which is why I give a general white range of 3.10–3.45 and a red range of 3.40–3.65 in my book.
Lower pH’s mean more acid and, in the case of, say, a sweet Idaho Riesling, a winemaker may want their pH’s to be lower than your California version, especially if they’re going to leave a lot of residual sugar in it to balance out that acid. That’s what acid levels are really all about — balancing flavor, style and microbial safety. Remember that most spoilage bacteria are happier at high pH’s so once you get over 3.75 you’ll have to store your wines with at least 25 ppm free SO2 and keep your containers scrupulously topped up.
As far as adjusting acidity, I always use straight up tartaric acid powder with reds, and sometimes will use a 2?3 tartaric 1?3 malic acid blend for whites, if I’m not going to take them through ML fermentation. Sometimes I find that malic acid adds a little apple-like “zing” to white or rosé wines. Weigh out the number of grams of acid you want to add (a small digital scale is an invaluable tool) and dissolve the acid in a small amount of water, just enough to liquefy the crystals. Dump into your juice or must, mix well and you’re good to go. Acidity should always be adjusted before pitching the yeast as anything you might do to drastically change the yeast cell’s environment can make them cranky and prone to spitting out stinky hydrogen sulfide or even stick mid-ferment!
As far as how much acid you’ll have to add to get to where you want to be, that’s a bit of a trickier question. pH is a non-linear measurement and, especially since wine is a buffered solution, it’s really hard to predict how a certain g/L acid addition will shift your pH. It’s something even professional winemakers have a tough time dealing with. Often all we can do is go on our experience with the vineyard and make more than one addition to try to not overshoot our pH goal.
You’ll have an easier time, however, if you can get your musts measured for total acidity in g/L or g/100 mL. Wine labs like Vinquiry in Windsor and Napa, California can help with analysis. Once you have your TA measured, you will know how much acid to add per liter to adjust your TA by the numbers. I like my California whites between 5.5–8.0 g/L and reds between 5.0–6.5 g/L, though it’s always a decision based on taste and balance of richness, flavor and other factors. Don’t add too much acid, however, if you want your wine to go through MLF. Most ML bacteria have a hard time going through fermentation if the pH is below 3.30.