The process of making white wine, whether from juice or grapes is dramatically different from the process of making red wine. Some key differences are skin contact time, ideal pH, fermentation temperature, aging time, oak usage and usage of malolactic fermentation. At a glance, making white wine is a bit simpler than making red wine. There are certainly a lot less processes involved on paper. In reality, this is not necessarily the case though. White wines are extremely delicate compared to their red counterparts. Even the mildest of flaws or faults can dominate the taste and ruin an otherwise good wine. Here are the steps that I take when making a white wine...
Crush and Press
If making white wine from grapes, the first step will be crushing and destemming the grapes. This can be done extremely quickly in the home with a hand crank style crusher-destemmer. Most crusher-destemmers have the ability to adjust the gap between the crushing wheels. Adjust this close enough to pop the berries, but not so close that it is crushing any seeds to avoid excess release of harsher seed tannin.
If you do not plan to ever make red wine, you can save a little money by just buying a crusher or stomping the grapes old school style. Because the grapes will be pressed immediately, the need to separate the stems is a little less critical than when making a red wine from grapes. Stems can actually be helpful when pressing the grapes, as they create nice little passages for the juice to more easily squeeze through.
Unless you are working with the cleanest, most perfect grapes, it is a good idea to treat the crushed berries with a mild 25-50ppm dose of SO2 in the form of potassium metabisulfite. This will mostly suppress any wild yeast, mold or bacteria, which gives a substantial competitive advantage to wine friendly yeasts which have a much higher tolerance to SO2.
Once crushed, pour straight into the wine press and begin pressing. Some people will allow up to a few hours of skin time on a white wine but any more is generally too much. Press straight into clear carboys, using a funnel with a kitchen strainer placed in it. The ability to see the juice will be helpful for the next steps.
Keep the grapes and juice as cold as reasonable possible during the crush and press steps. Picking in the early morning hours, just before sunrise is helpful as long as you do not have too much dew on the grapes.
An important consideration: Unless you are growing white grapes, or are able to pick them locally it is best to skip this step all together and buy juice for white wine. This way the grapes are crushed and pressed right off the vineyard which is ideal. This is not the case for red wine though. Flash extracted red wines that are not fermented with the skins and seeds are often thin and lack character as compared to a red wine that spends many days fermenting with the skins and seeds.
Cold Settle and Rack
After pressing the juice, allow it to settle out for one to three days. You will want to keep it cool at this stage (<45°F) to prevent any microbial activity. A spare fridge is helpful for this. Another simple way to keep the juice cool is to place the carboys in large plastic bins and fill the bins partially with ice water. You will need to add more ice about twice a day for this method.
Once the juice has settled, rack off of the settled lees into your fermenter. A white wine can be fermented in a food grade bucket, a food grade garbage can, barrel, 3/4 full carboy or any other food and fermentation friendly container. Now you have got your clean juice ready to to ferment and the process of turning that juice into wine can begin.
If making white wine from juice, start here:
Adjust if Necessary
Now that you have your pressed and settled juice, it is time to make a few measurements. At a minimum, check the pH and the specific gravity. You can check the TA at this stage, but I rarely will make adjustments based on TA.
Most white wines are should start fermentation at a pH in the range of 3.0-3.25. If your pH is much above 3.25, you will want to adjust down with a little tartaric acid. If you find that you are below about 2.9, you may need to adjust the pH up a bit with calcium carbonate or potassium bicarbonate. At these low pH's, you can really struggle to get the fermentation off the ground. A good pH meter is a worthwhile investment if you plan to stick with winemaking.
Next take a reading with your hydrometer. For wine, we generally use the °brix scale rather than the specific gravity scale on the hydrometer. This gives us a good indication of percent sugar by weight, which will be used to calculate the alcohol in the finished wine. The final alcohol or ABV of a wine fermented dry can loosely be calculated by the following equation: 0.57 * °Brix = % Alcohol. The °Brix used here is the original reading from before fermentation. All fermentations vary slightly on how much of the sugar is converted to alcohol (some will be converted to water and CO2), but this will get you plenty close enough for home winemaking purposes.
Your hydrometer reading should be somewhere in the 18-24°brix depending on the wine you are intending to make. If you find that the grapes are a little over ripe and have a higher sugar content than you want, you can adjust down with a bit of water. This is much less of a big deal with a white wine. To add water to a red wine would be a very very rare situation and a very painful decision for me. If you find that the grapes do not have enough sugar, you can "chaptalize" or add sugar in the form of table sugar or simple syrup. To determine how much sugar to add, 1.5 oz of table sugar per gallon will raise your sugars by roughly 1° brix.
Begin the Fermentation
To start the fermentation, bring the juice up to about 70°F. Don't do this too slowly, as some unfriendly, acetic acid forming yeasts can out-compete wine yeast in the 50-60°F window.
Choose a reliable yeast that will ferment happily at cooler temperatures and is not too nitrogen hungry. Many people will use d47 for white wine, but I find it to be a high hydrogen sulfide (H2S) producer if conditions are not just right. My absolute favorite white wine yeast is Renaissance Fresco. While this is technically labeled as a cider yeast, I find it to work wonders when making a crisp white wine.
Make a yeast starter to assure a good reliable start to the fermentation. Use of Go-Ferm will help strengthen your colony before adding to the wine. Once the hydrated yeast is showing signs of activity, add a bit of your juice to the starter. When you have nice vigorous starter that is within 10°F of your juice, pour slowly onto the surface of the juice. No need to stir it in.
Monitor for signs of fermentation. You should see small bubbles start to appear at around 12-24 hours. Once the juice is fermenting rapidly, cool the temperature down to help trap delecate and volatile fruity aromas. This is key to creating a fresh and vibrant white wine. With a non-H2S yeast like Renaissance Fresco, you can ferment as cool as 55°F with very little maintenance. You can use the cool water in bin method mentioned above to reduce the temperature or drop frozen 1L, 2L or 1 gallon bottles into the fermentation several times a day.
After about a day or two, feed the yeast with a good yeast nutrient like Fermaid K. You don't want to feed before your chosen yeast is fermenting actively, or you could encourage an unwanted yeast or bacteria to take off running. Once a good wine yeast is fermenting, most other microbes don't stand a chance of competing.
Stir and Monitor
Stir the wine twice a day throughout the fermentation. In the early stages, encourage a little air when stirring. This will help the yeast to more readily multiply and recover energy through aerobic respiration.
Smell the wine each time you stir it up. Look for even the slightest bit of H2S which will smell like sulfur or rotten egg. This indicates a stressed fermentation that is air or nitrogen starved, or fermenting outside of the ideal temperature window. Try to feed and aerate the fermentation back to the happy middle ground. Even the slightest bit of H2S smell now can lead to perceivable mercaptan later which gives the wine an off taste of garlic or burnt rubber. If the sulfur smell fails to go away with a little nutrient and air, you can treat with this product.
If you smell even the slightest bit of acetic acid (vinegar), or acetaldehyde (port wine or sherry smell) this can indicate an underfed yeast, or too much oxygen exposure. This is a little more rare during active fermentation but something to watch for, especially as the fermentation slows down. If caught early enough, the yeast is capable of reducing these compounds back to ethanol. A little yeast nutrient and more limited air contact can get you through fermentation in this case. After fermentation is complete it will be very important to sulfite judiciously if you are smelling any of oxidative smells.
If you smell vinegar, acetaldehyde, or ethyl acetate (nail polish remover) after fermentation is complete, DO NOT ADD YEAST NUTRIENT. In this case the more likely cause is a form of acetic acid bacteria (AAB). Any added nutrient at this stage will only feed the bad bacteria. The best course is to minimize air exposure, sterile filter (if you can) and sulfite to try to bind up at least the acetaldehyde.
Stabilize and Wait
Once fermentation is complete you will generally add enough SO2 to prevent malolactic fermentation from occurring. Malolactic fermentation will make the wine less crisp and refreshing, and more buttery and savory. Rather than continuously adjusting the SO2 to maintain protection, I prefer to make one large addition of 75ppm or more after completion of fermentation.
Some white wines like Chardonnay will benefit from malolactic fermentation. In this case, forget what I just said and add a nice reliable malolactic culture like CH35. You will sulfite after completion of malolactic fermentation in this case.
Should you Oak a White Wine? Not usually. A little oak can pretty quickly cover up the delicate fruit aromas of a white wine. Occasionally you will see a chardonnay aged on oak, or an oaked Riesling that is intended to be aged for many years. Do I oak my white wines?... no. At least I haven't made a white wine that I thought would benefit from oak.
Now that the wine is microbial stable, it is worth cold stabilizing before bottling. To achieve a cold stable wine, simply chill it for a while. You can do this in about a week at 30°F, or a couple months at 40-50°F, like out in your garage in the winter. Some of the tartaric acid in the wine will react with potassium and fall out as potassium bitartrate (cream of tartar). By cold stabilizing, you are encouraging these tartrate crystals to fall out before the wine goes into a bottle so you won't find any unsightly crystals in the bottles.
Now, all you have to do is wait for the wine to become crystal clear which can take anywhere from three to six months on average. Once clear, you can bottle the wine or back sweeten the wine. Most white wines are ready to drink in six months to a year. When doing any back sweetening, keep in mind that the wine will likely be served chilled. For this reason, it is best to taste test various levels of sweetness at the chilled serving temperature, rather than the storage temperature.
Degas and Bottle
Because white wines can be bottled relatively young, it is generally worth degassing to remove the majority of the dissolved CO2 in the wine. A degassing tool like this drill mount degassing tool can pretty quickly remove enough CO2 to bottle the wine. You don't need to get particularly carried away with a white wine, since the serving temperature is cold. CO2 is more soluble at colder temperatures, so unless the wine is very CO2 saturated, it is unlikely that you will see any bubbles when pouring, as they will remain dissolved. For Red wine, this is not the case... if a wine is bottled with a small amount of dissolved CO2, then warmed to 65-70°F to serve, you will often see a small bit of bubbles around the rim of the glass and may notice the taste and texture of CO2.
Cold Crashing (Optional)
Rather than back-sweeten, you can choose to intentionally stall out your fermentation and leave a bit of residual sugar. This is relatively difficult to do, but can achieve a fruitier, more aromatic wine when done right. To cold crash, you will want to chill the wine to around 30-35°F before the fermentation is complete. This will stall out the fermentation with a little unfermented sugar remaining. I have a spare fridge that I removed the bottom shelves in to fit two carboys. This works well for cold crashing and cold stabilizing. To cold crash effectively, leave the wine chilled until it becomes crystal clear which can take a couple months. Once clear, rack off the lees and add potassium metabisulfite to prevent malolactic fermentation/spoilage, and add potassium sorbate to prevent re-fermentation. At this point, you can bring the wine back up to normal cellar temperature.
Most wines fermented from juice will follow a similar procedure to that of white wine. This includes apple wine and many fruit wines that are not fermented with whole fruits or skins. If you are unable to get fresh juice in your area, or want to ferment in the off season, you can consider frozen juice pails or a high quality white wine kit.