20 Home Winemaking Troubleshooting Tips

In a notebook of fermentation hobby records, I have a lab report dated November 3, 1998. That soil pre-plant analysis from Fruit Growers Laboratory marked my start 20 years ago in becoming a home grape grower and vintner. Along the way, I have seen and addressed pitfalls and trouble spots that can come up on the way to producing a delicious adult beverage. Now, with 20 years of home winemaking experience myself, I am delighted to participate in this WineMaker magazine 20th anniversary issue. To keep the theme going I will share my 20 top troubleshooting tips for making every kind of wine.

Some faults and flaws are so common that just about any kind of wine can fall prey to them. Whether working with kits, making country wines from fruits and herbs, or processing fresh grapes, problems may show up. For my 20 tips, I’ll discuss some of these “universal” cases first, then go on to specific difficulties and solutions for different styles of wine.

Universal Tips

1. Pectin problems

These polysaccharides (sugar polymers) are common in fruits of all kinds where they contribute to the structure of plant cell walls. Breaking down the pectins in grapes or other fruits can help improve juice yield and prevent a pectin haze in the wine after alcoholic fermentation. There are enzymes for that purpose that can be applied to the fruit before fermentation or to the wine after. See my “Techniques” column in this issue (beginning on page 52) for a more thorough discussion of enzymes, particularly in country wines.

2. Suspended grape or fruit particles

Given sufficient aging time in bulk (carboys, barrels, or tanks), most fruit particles will settle out by gravity. If you have made a wine that seems resistant to settling, you may need to fine it, filter it, or both. When particles are difficult to settle, it can be because they have a common surface electrical charge, causing them to repel one another.

One good general purpose fining agent for negatively charged particles is hot-mix Sparkolloid NF from Scott Laboratories. It is a mixture of polysaccharides and a diatomaceous earth carrier that has a strong positive surface charge. It combines with negatively charged particles, clumping them together to drop out.

3. Yeast sediment

Yeast in the bottom of a wine bottle is not only unsightly, the gradual breakdown (autolysis) of that yeast can introduce unwanted flavors of bread, toast, or butter. While desirable in some sparkling wines, they are flaws in most other styles of wine. Racking is absolutely critical for taking the wine off of yeast residue and filtration is strongly advisable. At the same time, you want to avoid excessive exposure to air so you do not encourage browning (see tip #5). If there is still visible yeast residue in your final bulk container, you need to either rack the wine and store it a while longer or run the wine through an appropriate filter. Never try to rack off of a yeast layer directly into bottles; you will almost certainly transfer some of the yeast.

4. Tartrate crystals

Potassium hydrogen tartrate (cream of tartar) is a natural reaction product between potassium ions and tartaric acid from grapes, plums, lemons, and many other fruits. If a concentration develops in the wine that exceeds the solubility at a given alcohol level and temperature, crystalline precipitates form and drop out. In bulk storage, this presents no great problem, since you will rack off the sediment. Problems arise when dissolved tartrates are in the bottled wine and then that bottle is chilled below the solubility temperature. When this happens, crystals form in the bottle. Sometimes called “wine diamonds,” they look like little bits of glass in light-colored wines. In dark wines, the crystals pick up some of the pigment and appear as purple crystals. Although non-toxic and harmless, they are often perceived as a flaw by the consumer.

A good way to prevent the problem is a mirror of how it develops: Chill the wine. Make sure that you have lowered the temperature of the bulk wine below that at which the bottled wine will be stored and the tartrates will be left behind when you rack. In my mild California climate, I wait for a mid-winter cold snap where the overnight temperature drops just below freezing. I then expose my wine to the nighttime cold. If you have a spare refrigerator, you can choose the temperature and chilling period. Hold the wine at less than 40 °F (4 °C) for two to three weeks. A shorter time may suffice if you can cool the wine to around 25 °F (-4 °C). (Wines of 10% alcohol by volume or more freeze at or below this temperature.)

5. Browning

Very noticeable in white wines, a brown note is unattractive in most reds, too. The brown color is often accompanied by oxidized flavors of bruised apple, burnt sugar, and caramel. There are two steps to this tip: Prevention and correction.

Prevention involves keeping oxygen away from the wine. For white wines, begin right after pressing the juice, fermenting in a container sealed with an airlock, aging in topped-up containers, and keeping sulfite levels up. For reds, oxygen is beneficial during active fermentation, but after pressing it is time for topped-up containers and sulfites. Very slow oxygen uptake in a barrel can be beneficial to red wine aging, but there is usually enough exposure in home winemaking that no special steps are needed to achieve it.

For correction, particularly removing browning from white wines, fining with the synthetic polymer PVPP may help.

6. Suppressed aroma

Desirable fruity and floral aromas come about from two major sources. There are aromatic compounds in the fruit and skin, and yeast fermentation can produce fruity esters. To make sure you get the former, especially from aromatic grapes or fruits like lychees, consider the use of enzyme preparations that contain glycosidases to help free the aromas from bound sugar molecules. Warm fermentation encourages yeast esters, but it is usually best left to red wines since warm fermentation of whites will drive off native
fruit aromas.

7. Reduced sulfur odor

Smelling like rotten eggs or burnt rubber, volatile reduced sulfur compounds (VRS) can completely ruin the aroma of a wine. While several bad actors may be involved, hydrogen sulfide (H2S) is most prominent and smells distinctly different from the “just struck match” aroma of excessive sulfur dioxide (SO2). Several factors may contribute to the problem, which is usually the result of stressed yeast. Avoid excessive sulfur use in the vineyard, keep the fermentation temperature in a good range for your chosen yeast strain, and manage your nutrient program with appropriate use of a complex yeast nutrient or diammonium phosphate (DAP).
If VRS rears its ugly head in spite of your best efforts, treatment is available. Use copper sulfate 1% solution to add 0.5 ppm of copper to your wine (the legal maximum for commercial wines) and rack off the sediment. Alternatively, use a fining agent like Lallemand’s Reduless, which is naturally rich in copper.

8. Stuck fermentation

As you take daily Brix or specific gravity (SG) readings during your fermentation, it can be disheartening if you notice the sugar consumption rate dramatically decreasing. Stable readings above zero °Brix (or 1.000 SG) over a few days indicate that your fermentation has stopped before completion — it is stuck. Prevention is a lot like Tip #7: Keep the temperature appropriate and use recommended nutrients. One additional cause may be a sugar level so high that alcohol becomes toxic to the yeast. Another is excessive sulfite additions to the must. In any case, the dying yeast releases fatty acids that inhibit a re-inoculation of fresh yeast.

If simple re-inoculation with fresh yeast does not work, you will need to treat the stuck wine with yeast hulls to remove toxic compounds, then make a vigorous yeast starter and progressively add portions of stuck wine to it. If the sugar is so high that complete fermentation will be impossible, either add water and try again or make a sweet dessert-style wine.

9. Excess SO2

Since you want to avoid a stuck fermentation, you do not want to begin with excessively high levels of sulfites (SO2, sulfur dioxide, potassium metabisulfite). A purchased juice or must may have had high sulfite additions to help with shipping. Fresh fruit may need higher additions than usual if mold or rot is present. And winemaker addition mistakes may occur. Adding up to 50 mg/L (parts per million, ppm) sulfite to crushed must is routine and adding up to 100 mg/L should present no problem. These levels will dissipate and react quickly, allowing yeast to do its work. If you find a level higher than these, or add too much by mistake, you need to eliminate it before continuing. A brisk aerated racking may take care of the problem. If not, use ordinary drugstore 3% hydrogen peroxide. One mL per gallon/4 L of juice will remove 10 mg/L of
free sulfite.

Style-Specific Tips

Kit Wines

10. Gassy wine

While a little bit of carbon dioxide spritz might be welcome in some styles, it is usually considered a flaw in dry table wine. Some kits are put together for very rapid production, advertised as requiring as little as four weeks. These rapid kits are prone to retaining carbon dioxide from fermentation that would dissipate naturally over months of aging and racking conventional wine. To remove excess gas, apply mechanical stirring, use a vacuum, or sparge with nitrogen or argon.

Stirring requires just a battery-powered drill and a plastic or stainless steel wine whip (of which there are numerous options on the market). For applying vacuum, you will need a vacuum pump or vacuum aspirator. The Gas Getter is compressed-air driven and the Blichmann WineEasy is an electrical vacuum pump. For a gas system using argon or nitrogen, you need to assemble various components at a local compressed gas vendor.

The most important lesson with any approach is to be patient. Degas your wine following kit or equipment instructions, but then stopper the container and leave it a few hours. Check it again. You may need to repeat the treatment.

Country Wines

11. Even more pectins

Grapes are not especially high in pectins, but some other fruits can be very problematic. If you are working with cranberries, gooseberries, quinces, and a few others, it is worth taking special care about avoiding a pectic haze. The tip here is to have both kinds of pectic enzyme treatments on hand; one to apply to the must, and another for the finished wine.

12. Too little or too much alcohol

When making country wines, a sugar addition is almost always necessary. Few fruits come close to the 20 to 26 °Brix of wine grapes. Applying a factor of 0.55 x °Brix to estimate alcohol, a grape level of 22 °Brix can produce (22 x 0.55) = 12.1% ABV. If you want to make nectarine wine, native sugar will be only about 8.5%, producing just (8.5 x 0.55) = 4.7% ABV. You will need to add sugar to produce a table wine. You can look up fruit sugar content in this table from USDA: www.ars.usda.gov/ARSUserFiles/80400525/Data/Classics/herr48.pdf or measure juice sugar level with a refractometer or hydrometer.

Adding 1⁄8 lb. (0.125 lb, 56.7 g) of sugar to a gallon (3.8 L) of juice adds 1 °Brix. If you want to raise a gallon
(3.8 L) of nectarine juice to 22 °Brix, calculate the difference (22-8.5 = 13.5) and multiply by 0.125 (13.5 x 0.125 = 1.7). So you need 1.7 lbs. (0.77 kg) of sugar for your gallon (3.8 L) of juice. But do not overdo it!
Suppose you want strong nectarine wine and add 3 lbs. per gallon instead. Now you have (8.5 + (3/0.125)) = 8.5 + 24 or 32.5 °Brix. Multiplying that by 0.55 predicts 17.9% ABV — quite possibly above what your yeast can tolerate, resulting a stuck fermentation. Look up, measure, and calculate carefully for sugar additions.

Vinifera grapes

13. Mold and mildew

Commercial grape growers are pushing climate boundaries and home winemakers are going even further. Sometimes, that means vinifera wine grapes may develop problems. Warm, humid conditions can lead to mold and mildew. If you encounter (or grow) grapes with visible mold or mildew, sorting is the most important step you can take. Remove and discard damaged fruit. (When he was the winemaker at Quivira Vineyards in Healdsburg, California, Grady Wann liked to tell fruit sorting staff, “If you wouldn’t put it in your mouth, don’t put it in my wine.”) Beyond that, sulfite more than usual, keep things cool, and use enzymes for rapid maceration. Do not cold soak. If you detect moldy character in the young wine, try bentonite fining to remove some of the moldiness.

Red Vinifera grapes

14. High alcohol

This problem comes about from pushing for maximum ripeness, especially in warmer climates. Instead of the 23 to 25 °Brix that you want, you may find yourself with 27 to 30 °Brix, particularly if crushing and soaking includes some raisins in the clusters (Zinfandel is notorious for this). To complete a dry, balanced table wine, you will need to add water. Commercial wineries are allowed to add water to replace that lost to dehydration during fruit handling, so that is what you are doing.

To calculate, estimate that every 100 lbs (45 kg) of crushed must contains 6 gallons (23 L) of juice. From there, you multiply your estimated volume times measured Brix and divide by desired Brix to find your needed total volume. Add water accordingly. Make sure the water is chlorine-free; distilled is best, since “lost due to dehydration” is pure water vapor.
200 lbs. (91 kg) of Zinfandel must
Estimated 12 gallons (45 L) of juice
Measured Brix: 32
Desired Brix: 25
(12 x 32)/25 = 15.4 gallons (58.3 L) needed total volume
15.4–12 = 3.4
So add 3.4 gallons (12.9 L) of water

15. Astringency

Tannins in red wine give it a pleasant “grip” on the tongue and palate. At high levels, these sensations are unpleasantly astringent. If you find that you have made an astringent red wine, look into using a protein fining agent to tame it. Egg whites have a long tradition in Europe and are considered a mild treatment. Other choices include isinglass or gelatin. To apply egg whites, use the whites of 1⁄2 an egg per 5 gallons (19 L) of wine. Whip the egg whites with a small amount of water and wine, stir into the wine, and rack off in 4 or 5 days. For isinglass or gelatin, follow package directions.

16. Bitterness

Related to astringency, bitterness is distinguished by molecular size. The tannins responsible for astringency are polymers of phenols — polyphenolic compounds — from a group called flavonoids. Monomeric flavonoids, those that are not linked into polymers, are more bitter than astringent. These can be moderated by protein fining as described above, but are separated here for a specific fining agent with an advantage. Nonfat milk fining is a protein addition that will drop various flavonoids. At the same time, some lactose dissolves into the wine. Lactose is not fermentable by Saccharomyces and does not lead to refermentation. The slight sweetness it imparts will help balance residual bitterness in the wine, just like putting sugar in your tea. To use nonfat milk, stir 100 to 250 mL of fresh nonfat milk into every 5 gallons (19 L) of wine. Rack off of the curds in 4 or 5 days.

White Vinifera grapes

17. Protein haze

In red wines, natural grape proteins combine with natural tannins and drop out during fermentation and aging. In whites, tannins are very low. Proteins may persist into the finished wine. Just like frying an egg white, heating up wine with protein in it can cause coagulation, which then presents as a haze in the wine. If you always keep your wine at cellar temperature or below, this will probably not be a problem. If you can’t do that, consider fining with bentonite.

Like tannins, bentonite will combine with proteins and drop them out. Bentonite can be applied before or after fermentation; follow package instructions for dosage rates.

Native/hybrid grapes

18. Slippery pressing

Some of these grape varieties, when used for white or rosé wine, can present problems in pressing. Crushed fruit may be slippery or gummy, making juice extraction more difficult. Adding pectic enzymes to the crushed fruit may help juice yield. In the press, adding a layer of rice hulls after every few inches (cm) of must addition can serve as a filter aid and provide flow channels for the juice. Rice hulls are food-grade, inexpensive, will not have an impact on taste or aroma, and are widely available at homebrew shops.

Sparkling wine

19. Yeasty character

Some products of yeast aging (autolysis) are desirable in sparkling wine. In young wine made by the traditional or Champenoise process, though,  the yeasty character can be overwhelming. To overcome this, you have two choices.

First, you may disgorge your sparkling wine as soon as the secondary fermentation is complete. Taking the wine off of the residual yeast will halt further development of yeasty character.

Second, you may age your wine on the yeast for several years to mellow out and then process it as “late disgorged” sparkling wine. These are often considered premium products at sparkling wine producers. My favorite local sparkling house, Gloria Ferrer, has a 2006 late disgorged Carneros Cuvée in current release. So if you have the patience, try longer aging.

Fortified wine

20. Stopping as desired

These wines have grape (or other) distilled spirits added, raising the alcohol level and making a sweet wine stable against refermentation.

A technique for achieving a desired balance of sweetness and alcohol is to stop the fermentation at a desired sugar level and add spirits to stabilize. It works, but modern wine yeasts do not easily stop in the middle of a vigorous fermentation. When your wine gets down to two or three °Brix above your target sweetness, press off the skins. Add the calculated high-proof spirits, chill the fermenting wine/spirit blend to near freezing (I bury a stainless steel Cornelius keg or a PET plastic carboy in a bucket of ice), and add 100 mg/L (ppm) of sulfite. Keep cold two or three days, add another 50 ppm of sulfite, and allow the wine to come to cellar temperature. Put an airlock on, and if the wine resumes active fermentation, chill and sulfite again. If no fermentation starts, you did it! Age, rack, sulfite, and bottle as for any other wine.

One Last Note

Finally, tying together many of these tips, always keep an eye on cleaning and sanitizing! Wash all equipment with quality winemaking cleaners like TDC, PBW, sodium percarbonate, or One-Step and rinse thoroughly. Before use, sanitize with iodophor, StarSan, or a mixture of citric acid and potassium metabisulfite. Keep it clean to make tasty, unspoiled beverages!