Wine Production Techniques Guide
The Cold Soak and the Skin Soak
The cold soak is used on a lot of red grape varieties, as it allows the stubborn skin pigments to become dissolved in the juice and thus provide a richer color. Here in the Pacific Northwest, Pinot Noir is the most prominent grape it’s used for. The skin soak is, in effect, the same technique as the cold soak but is is much shorter, as is appropriate for white wines. Soaking on the skins before pressing is a technique that provides a lot of fruity character, and the must will acquire more tannin. Bonus? The grapes will also give up more juice when pressed.
The grapes must be perfect. Broken skins, mold, bunch rot, or dirt cannot be allowed for a cold or skin soak. Infections will raise their ugly heads. Always use pectic enzyme and sulfite (SO2) your must to at least 30 parts per million (ppm) to avoid any wild fermentation.
For white grapes, once they are crushed and have had the pectic enzyme and SO2 added, simply allow them to sit on their skins for 2 – 12 hours. You can chill this must, but it is not required. However, chilling red must to about 50℉ is vital. Once chilled, allow the must to soak for about three days at 50F or lower.
The easiest way for small-batch winemakers to cold soak is to freeze water in a couple of plastic gallon milk jugs. (Make sure the jugs don’t split, so you don’t dilute the must.) Alternate jugs between the freezer and the must as needed to keep the temperature low. Remember to also punch down the grape skins once or twice a day, as this will not only release CO2 but also help keep the temperature of the must even. Keep your fermentor covered to prevent the escape of the SO2.
If any signs of wild fermentation show up in either soak, immediately cease the cold soak. Pitch your yeast and warm everything up to fermentation temperature.
After the cold soak, slowly raise the temperature to fermentation temperature and proceed.
Warming Up Must
Even though it’s 100℉ as I type this, I know we will receive our grapes in colder weather. (It might be downright icy at times.) Use the method I detailed above to raise the temperature in your fermentor, but use hot tap water instead of frozen jugs. Keep changing the warm jugs until you reach your fermentation temperature. Then wrap the fermentor with a FermWrap or an electric blanket and place it in a warmer room.
Note: If you have more than 100 pounds of must in a single fermentor, it will start to generate noticable heat on its own. Keep an eye on the wine so it does not get over 80℉ and thus ferment too fast. This will reduce the quality of the final wine.
Tips for Pressing Off Juice/Wine
Advice abounds on how to avoid excessive tannin when pressing grapes for wine. However when you make small batches of wine at home using the typical basket press, you will not have problems pressing off too much tannin. That said, there are other things to consider.
For example, you may decide to ferment the free flow wine separately from the pressed wine. (“Free flow” is the what flows out of the press before any pressure is applied.) The pressed wine will mature faster than the free flow wine and be much lighter in body and flavor. I don’t think it’s worth the effort unless you can get more than fifteen gallons of free-flow wine. Then you will get about three gallons of pressed wine.
Make sure you have a good-sized sieve that can fit into a one-gallon or two-gallon bucket and will together fit under the press spout. You’ll also want a funnel that will be big enough to handle the flow from the bucket into the carboy. Don’t skimp on funnel size! If you do, there will substantial slop and spills and wine loss.
Related, remember that pressing off is sloppy work no matter your funnel size. So make sure the press and the fermentor are in an area you can clean up easily by hosing it down.
Many of the world’s best red wines go through malolactic fermentation (“MLF”). This is not a yeast fermentation but a bacterial one, and little alcohol is produced. MLF occurs when malolactic bacteria convert malic acid to lactic acid. Malic acid is a harsh acid of unripe fruit like green apples, and lactic acid is that softer “tang” found in cheese or yogurt. You will typically want MLF in any red where a finished softness of acidity and an ability to age well is desired.
However if your grapes are overripe and thus have a low acid level to begin with, MLF can make a flaccid and dull tasting wine that ages less well than you desire. What fruitiness was in the wine before MLF will be gone and the stabilizing acidity will be dramatically lowered. At this point, avoid MLF and increase the acidity of the must.
Most red wines will benefit from MLF, but it’s considered an infection in some wines. It’s particularly undesirable if you want a fruit-forward wine like Lemberger, Riesling, Muscat or most Chardonnays. (Big, buttery Chards can, and often do, undergo MLF but grapes appropriate for that style rarely come from the PNW.)
For MLF to occur the must should have the following characteristics:
- Total acidity (TA) no less than 0.070 but no more than 1.00
- pH no less than 3.3 but no more than 3.7
- a specific gravity (SG) of 1.05 or below
- SO2 of less than 30ppm
Typically, all of this information should be given to you when you receive your grapes or juice. Sometimes, though, all you get is the TA and pH. In that case, use your hydrometer to get the SG. The SO2 is what you add. Measure carefully.
If you need to adjust your acid up or down, please see our must adjustment handout. If you need to add acid be sure it’s tartaric acid. This is the acid of balanced wines. If your grape juice or must is over 1.00 TA, you got very under ripe grapes that are sour. Even with careful measurement, your TA and SG will be off (at that point, the acid content can mask sugar content). Unless it is or has been a horrifically cold and wet fall, don’t repurchase those grapes. Find a different grower.
Malolactic cultures come in a variety of forms, and you can add them at different times depending on your desires and schedule. You can add them at the tail end of primary fermentation or after the wine is in the carboy for secondary fermentation. Be aware, though, that the longer you delay adding the malolactic bacteria, the harder it will be for MLF to complete. This is because once primary fermentation ends, you will be adding SO2 regularly (up to 50 ppm), and typically your fermentation temperatures will be dropping. MLF occurs best in warm, low oxygen environments. And SO2 is added in large part to prevent bacterial growth, so MLF is caught in that. In a cooler environment with more SO2, MLF will be slow and may take months to finish. This is why if you want to prevent MLF, or any other bacterial invasion, you add SO2 to your wine regularly after every racking and before bottling.