How to Remove Tannins from Grapes for Smoother Wine

Understanding Tannins and Their Impact

Tannins are naturally occurring polyphenols that give red wines their characteristic structure, color stability, and age-worthy potential. While crucial for certain styles, an excess of tannins, especially those derived from seeds and stems, can lead to undesirable bitterness and a rough, mouth-puckering astringency. The goal of tannin management, particularly in home winemaking, is to find the right balance—removing harsh, green tannins while preserving desirable ones. The process can begin in the vineyard and continues through crushing, fermentation, and aging.

Vineyard and Harvest Techniques

Before the grapes even reach the winery, several viticultural practices can influence the final tannin profile.

Canopy Management and Light Exposure

Grape skins produce tannins partly as a defense against UV light. Proper canopy management involves strategic leaf removal to control the amount of sunlight reaching the grape clusters. More exposure can lead to higher tannin levels, while shading can result in fewer, potentially greener, tannins. The timing of leaf removal is critical, as it primarily affects skin tannins.

Irrigation and Ripeness

Water availability during the growing season affects berry size, and therefore, the skin-to-pulp ratio and tannin concentration. Deficit irrigation can result in smaller berries with a higher tannin concentration, while irrigating during the final stages of ripening can soften existing tannins. The timing of harvest is paramount; allowing grapes to reach full phenolic ripeness ensures that the tannins become softer and more polymerized, reducing their astringency. Unripe grapes, conversely, contain harsher, less-desirable tannins.

Managing Tannins in the Winery

Once harvested, winemaking techniques offer the most direct control over the extraction and removal of tannins.

Controlling Maceration

Maceration is the process where grape skins, seeds, and stems are left in contact with the juice.

Cold Soaking: A pre-fermentation maceration at low temperatures (50-60°F) for several days allows for a selective extraction of color and fruity aromas while minimizing the harsher tannins extracted later by alcohol.
Extended Maceration: Post-fermentation, extended skin contact can allow for further polymerization of tannins, leading to a softer, more integrated mouthfeel, though it can also increase extraction. The decision depends on the grape variety and desired wine style.
Cap Management: Techniques like 'punching down' (physically pushing the floating cap of skins down) or 'pumping over' (circulating juice over the cap) increase skin-to-juice contact, thus increasing tannin extraction. Gentle, less frequent cap management can help control the amount of tannins extracted.

Fining Agents

Fining is the process of adding a substance to the wine that binds to specific compounds (like tannins) and precipitates them out, clarifying the wine and softening its mouthfeel.

Protein-Based Fining Agents: Historically, fining with egg whites (albumin) was common, as the protein binds to and precipitates tannins. Other protein-based options include gelatin, casein (milk protein), and plant-based alternatives like pea protein for vegan winemaking. Gelatin is particularly effective for highly tannic wines but should be used carefully to avoid over-fining.
PVPP (Polyvinylpolypyrrolidone): A synthetic polymer, PVPP is very effective at removing bitter phenolics and can be useful for reducing astringency in wines made from under-ripe grapes.
Isinglass: Derived from fish bladders, this is less aggressive on tannins than gelatin but still an option for clarification.

Filtration

Membrane filtration, particularly microfiltration (MF) and ultrafiltration (UF), can also be used to remove tannins, though it is a less selective method. UF is more effective than MF for removing tannins due to its smaller pore size. However, more intensive filtration may strip away desirable compounds and alter the wine's character. Winemakers often prefer natural settling (racking) to minimize filtration.

Comparison of Tannin Removal Methods


Method	Principle	Application	Pros	Cons
Cold Soaking	Controlled, pre-fermentation maceration.	Before fermentation of red grapes.	Extracts color and fruity aromas while limiting harsh tannins.	Less effective for removing tannins already present post-fermentation.
Fining (Protein)	Adding proteins (gelatin, egg white) to bind and precipitate tannins.	Post-fermentation, in barrels or tanks.	Highly effective for reducing bitterness and astringency.	Risk of over-fining, potentially stripping desirable characteristics.
Fining (PVPP)	Adding synthetic polymer to bind bitter phenolics.	Post-fermentation, in tanks.	Very efficient for correcting astringency from unripe fruit.	Can be less selective, removing some desirable compounds.
Micro-oxygenation	Controlled addition of small amounts of oxygen.	During or after fermentation, in tanks.	Softens tannins by encouraging polymerization, mimicking barrel aging.	Requires careful monitoring to prevent unwanted oxidation.
Oak Aging/Alternatives	Adding oak tannins (barrels, staves, etc.) to complex and soften existing tannins.	During or after fermentation, in barrels or tanks.	Softens and integrates tannins, adds flavor complexity.	Imparts additional flavors that may not be desired.

Process for Removing Tannins from Grape Juice

For those making non-alcoholic juice or needing to treat grape juice before fermentation, the process is slightly different.

Selection and Ripeness: Use fully ripe grapes to begin with, as they will contain softer, more polymerized tannins than unripe ones.
Heat Treatment: For very tannic grapes, a short heat treatment (e.g., immersing whole grapes in hot water for 15-20 minutes) can reduce tannins, as some types degrade at high temperatures. Follow immediately with an ice bath for faster skin peeling.
Peeling Grapes: Since skins are the primary source of tannins, removing them is a direct way to reduce astringency. Blanching in boiling water for 5-10 seconds, then moving to an ice bath, makes the skins easy to peel.
Enzymatic Treatment: Add pectinase enzymes to the juice. These enzymes break down cell walls, facilitating the extraction of desired compounds but can also be combined with other techniques to help settle out undesirable tannins.
Use Fining Agents: Add fining agents like gelatin or casein directly to the juice. The agent will bind to the tannins, forming a precipitate that can be removed by racking (siphoning the clear juice off the sediment).

Conclusion

Successfully managing tannin levels in grapes, whether for wine or juice, requires a multi-pronged approach that begins in the vineyard and continues through processing. By controlling variables such as grape ripeness, maceration length, and temperature, and by employing targeted techniques like fining and micro-oxygenation, producers can achieve the desired balance of texture, flavor, and astringency. The key is to start with a tasting trial to determine the necessary adjustments before treating the entire batch, as each grape variety and vintage will present unique challenges and opportunities. The right combination of techniques ensures that the final product is both pleasing to the palate and structurally sound. For further reading on fining agents, you can explore resources from winemaking suppliers like WineMaker Magazine.

What are Tannins in Grapes?

Astringent Compounds: Tannins are phenolic compounds found in the skins, seeds, and stems of grapes, responsible for astringency.
Impact on Mouthfeel: They create a drying, mouth-coating sensation by binding to proteins in saliva.
Ripeness Matters: Unripe grapes have harsher, less desirable tannins, while ripe grapes contain softer, more integrated tannins.
Color Stabilizers: In red wine, tannins extracted from grape skins help to stabilize the wine's color over time.
Varietal Differences: Tannin levels can vary significantly depending on the grape variety and growing conditions.

Fining Agents for Tannin Removal

How They Work: Fining agents are added to wine or juice to bind with tannins and other particles, causing them to precipitate to the bottom.
Protein-Based: Gelatin, egg whites, and casein are traditional protein-based fining agents that effectively remove tannins.
Vegan Alternatives: Plant-based protein fining agents, such as pea protein products, are available for vegan winemaking.
Synthetic Options: PVPP (Polyvinylpolypyrrolidone) is a synthetic polymer that is very effective at removing bitter tannins.
Careful Dosing: It is crucial to conduct a small-scale trial with fining agents first, as over-fining can strip the wine of desirable characteristics.

Winemaking Methods for Tannin Control

Maceration Period: The length of contact time between grape skins/seeds and the juice during fermentation directly impacts tannin extraction.
Fermentation Temperature: Higher fermentation temperatures can increase the extraction of tannins.
Micro-oxygenation (MOX): A process of controlled oxygen exposure can help polymerize and soften tannins, mimicking the effects of aging.
Racking: Siphoning clear wine from the sediment (lees) over time helps remove precipitated tannins and other solids.
Aging: Extended aging, especially in oak barrels, allows tannins to soften and integrate further into the wine's structure.

Home Methods for Reducing Astringency

Peeling Grapes: Removing the skins, where a large concentration of tannins resides, can significantly reduce astringency in grapes used for juice or fresh consumption.
Heat Treatment: Blanching grapes briefly in boiling water can help in peeling and may reduce tannins, but it's best for juice rather than winemaking.
Freezing: Freezing grapes can be a simple way to reduce astringency and is a good option for a quick snack.
Blending: Combining a high-tannin grape must with a low-tannin must can help balance the overall profile.
Aging: Much like in commercial winemaking, time is a natural way to soften tannins, though this is only effective for wine.

F.A.Q.s

How does controlling fermentation temperature help manage tannins?

Higher fermentation temperatures increase the rate at which alcohol extracts tannins from the skins and seeds. By keeping the temperature lower, winemakers can limit the extraction of more bitter tannins, producing a smoother, more fruit-forward wine.

Can I remove tannins from grapes after I've already made wine?

Yes, tannins can be removed from finished wine through a process called fining. You can add fining agents like gelatin, casein, or PVPP, which bind to the tannins and cause them to settle out. This allows you to rack the wine away from the bitter sediment.

Is it possible to remove all tannins from grapes?

It is nearly impossible to remove all tannins, nor would you want to in red wine, as they provide structure and color. The goal is to reduce aggressive, unpleasant tannins to achieve a more balanced and softer mouthfeel, not to eliminate them entirely.

What are the main sources of tannins in grapes?

The primary sources of tannins are the grape skins, seeds (also called pips), and stems. Seeds are often associated with harsher, more bitter tannins than the softer, more complex tannins found in skins.

How does ripeness affect tannins in grapes?

As grapes ripen, the tannins in the skins and seeds polymerize, or combine into larger molecules. This process makes the tannins feel less astringent and more integrated on the palate. Unripe grapes have harsh, green tannins that can be very bitter.

What is micro-oxygenation and how does it relate to tannins?

Micro-oxygenation (MOX) is the controlled, very slow introduction of small amounts of oxygen to the wine during or after fermentation. This helps to polymerize tannins and stabilize color, resulting in a softer mouthfeel and a less aggressive tannic profile.

What is the difference between cold soaking and extended maceration for tannin management?

Cold soaking happens before fermentation to extract color and aromas with minimal harsh tannins. Extended maceration occurs during and after fermentation, using alcohol to extract more tannins over a longer period, aiming for more complex, integrated structure rather than simply reducing them.