What Are Tannins in Wine?

Wine barrels and tannins


Tannins are essential to wine.

Virtually all families of plants, including wine grapes have natural “tannins”, and they exist in the grape skins, stems and seeds as well as oak used for wine barrels.

However, tannins that develop over time in wine are actually very different. This is because the chemical make-up of the tannins actually changes during both the winemaking process as well as bottle aging.

Tannins are a group of phenol compounds found in most plants called “polyphenols”. These polyphenols are largely responsible for giving wine a defined structure, or body, adding balance, complexity and structure, as well as acting as a natural preservative to enable a wine to age longer.


Even though tannins don’t have any smell themselves, they are also indirectly responsible for a wine’s aroma.

In slowly reacting with the wine’s alcohols and esters (acidic alcohols), they gradually erode the initial flowery, fruity aromas found in young wine thus enabling the “toasted oak” notes introduced by the oak barrel aging process.

Tannins also affect the colour of red wine. The bluish-red or violet colour of a young red wine formed by the pigments in the grapes are gradually replaced by deeper, brick-red or dark cherry colours created as long polymer chains linking the grape pigments to the tannins.


The term ‘tannin’ comes from the ancient practice of using extracts from plants to cure leather (the process still referred to as ‘tanning’).

This process exploits one of the key properties of tannins: they have a strong tendency to link up with a range of other chemical entities, most particularly proteins, and when applied to animal hides for example, tannins cross-link the proteins, turning something rather soft and floppy into a material that’s tough and inert enough to make shoes, belts and saddles.

There are two main types of tannins: hydrolyzable tannins and non-hydrolyzable tannins (also called “Proanthocyanidins”). Hydrolyzable tannins (meaning that they are able to be split up and broken down by interacting with water) are commonly found in acidic form in the bark and wood of oaks and other plants, or more specifically, the oak barrels used for ageing wine.

Non-hydrolyzable tannins are often found in other plant sources such as tea, pomegranates as well as grape seeds and grape skins.


Tannins are also one reason why it is recommended that you allow a wine to ‘breathe’ or aerate before drinking it.

By decanting a wine, exposure to oxygen softens the tannins, especially in young red wines with “younger” and more prominent tannins.

White wines have much lower tannin levels because white wines are not typically fermented with their skins or seeds as in red wine production, so the extraction of tannins is minimal. In contrast, the ability to age white wine derives primarily from acidity, but also from the alcohol content and fruit extracts.


Should a wine present unpleasant “tannic” sensations, then chances are that the tannins were “altered”.

A well-made red wine will always present noticable tannins on the palate. However, these “natural” tannins should always be softer, and “integrated” into the wine and not be perceived as “rough” or “puckering”.

It is common practice to add industrial tannins, especially in dry powdered form, to “correct” the tannin levels in a wine made from inferior quality grapes. These wines, on the other hand are often accompanied by an unpleasant mouthfeel.

Learn more about the effects of aging on tannins on our Ronda Wine Tour, as well as the differences between Crianza, Reserva & Gran Reserva!


What are Minimal Intervention Wines?


Minimal intervention winemaking is the practice of making wine in the most natural way possible, without pesticides, chemicals or unnecessary additives.

In order to mass produce wine, a vineyard would typically grow and harvest the maximum amount of grapes possible. That means growing more than 12kg of grapes per vine, resulting in an output of around 10 bottles of wine from each individual plant.

Vineyards focused on quality on the other hand, carefully grow at lot less grapes and eventually harvest only around 1kg of grapes from each vine. Which means no more than 1 bottle of wine from each vine.

When a vineyard focuses on quantity, they will be utilising a significant amount of pesticides and anti-fungal treatments to ensure maximum yields, especially in climates with harvest-time humidity and problem diseases such as mildew.

The Role of Sulphites

The most common additive is sulphite (or sulfite), an inclusive term for a preservative that’s widely used in winemaking, as well as across the food industry in general.

Sulphite-free wines refer to a style of winemaking where no additional sulphites have been added during the winemaking process, and technically these are termed as “No Added Sulphite” or “Natural Wines”.

Sulphites (or SO2) are used primarily as an antioxidant and antibacterial additive.The amount of sulphites that a wine can contain is highly regulated around the world. Any wine containing more than 10 mg/l (or ppm, parts per million) of sulphites must include text on the wine label that references the words ‘contains sulphites’.

Sulphites play an important role in preventing oxidization and maintaining a wine’s freshness, and since the winemaker has very little control over the wine’s storage conditions from the time the wine leaves his winery, SO2 is almost always a necessity used to help guarantee that the bottle of wine you open will be in the exact condition the winemaker intended.

The maximum levels allowed by the EU are 150 mg/l in dry reds, 200 mg/l in dry whites and rosés, 235 mg/l in sparkling wines, and 250 mg/l in sweet white and rosé wines.

Maximum levels for dry wines outside Europe are generally 350 mg/l in the US, 300 mg/l in Chile, 250 mg/l in Australia, 130-180 mg/l in Argentina and 150-160 mg/l in South Africa.

Considering that dried fruits can have levels equivalent to 1000 mg/l, if you regularly eat dried fruit without any adverse reactions, then you are probably not allergic to sulphites.

Are Organic Wines Lower in Sulphites?

Many wine producing countries (USA, Chile, Australia, South Africa) have already established standards for organic wines, and the EU has also standardised legislation with regard to the organic winemaking. Organic wine must of course be produced using organic grapes, however Sulphites can also be added, but at a much lower level than regular wine. The new EU approved ranges for S02 content in organic wines must be: less than 100 mg/l for dry reds, 150 mg/l for whites and rosés, and 220 mg/l for most sweet wines.

Additionally in the US you will find more wines labeled ‘made from organically grown grapes’ as opposed to labeled as true ‘organic wine’, because in the US ‘organic wine’ must not have any added SO2.

Are Sulphite-Free Wines Better?

In reality, totally 100% sulphite-free wines do not exist. There are always a tiny quantity of naturally occurring sulphites in every wine resulting from the yeast metabolism during fermentation. However, the levels are very low and they are harmless, and usually under a level of 10 mg/l.

“Sulphite-Free” wine is more of a marketing gimmick, as the naturally occurring sulphites would have to be removed using a chemical extraction process, and the wine would no longer be a “natural wine”.

Red wines without any SO2 will usually have a much shorter shelf life and need to be kept in perfect cool storage conditions. White wines are even more prone to oxidation and the development of aldehyde off-odours, so adding SO2 is particularly important, and for this reason white wine will usually contain much more Sulphites than red.


On your Ronda Wine Tour, you will taste at wineries that use the minimum of sulphites (usually around 20-40 mg/l) and even produce “No Added Sulphite” wines (less than 10 mg/l).

The difference between Reserva & Gran Reserva?

Ageing of Spanish Wine


Roble, Crianza, Reserva & Gran Reserva, which is best?

Spain is one of the few wine producing countries where practically all wine is only released to the market when it is “ready to drink”, and has followed appropriate aging, not only in oak barrels but in the bottle as well.

Hence, the system of wine classification to reflect the aging of the wine as “Roble”, “Crianza”, “Reserva”, and “Gran Reserva” that essentially guarantees the aging time that a wine has spent both in barrel and bottle.


How long are the wines aged with this classification? Surprisingly these categories are similar, but not entirely consistent across Spain, starting with “Roble” (oak) which generally refers to young wine aged for short period of only a few months in total (both in barrel and bottle).


All “Crianza” wine produced in the regions of Rioja and Ribera del Duero require a minimum of two years ageing, of which one year must be completed in barrel and the other in bottle. Other regions in Spain also require a total of two years aging for Crianza status, but with a minimum of only six months in oak.


In Rioja, “Reserva” wines must be aged a minimum of three years, with one year of that time in barrel, and “Gran Reserva” wines must be aged for five years, with two years in barrel at the minimum.

Reserva wines across the rest of the country have a lower minimum barrel ageing period of 18 months. Another consideration is that only in Rioja is the size of the barrel limited to the standard 225L “Bordeaux barrel” which facilitates a greater contact of wine with wood.

That two-for-one offer on “Gran Reserva” at your local supermarket may not be such a tempting deal after all.

It follows that, “Reservas” and “Gran Reservas” should theoretically be “better wines” because they have been selected for extended ageing over others, but in direct contrast they are not necessarily richer, higher quality or more powerful wines for the exact same reason.

“Reservas” may actually be “less powerful wines” precisely because they have been aged for a longer period in older barrels especially for the sole reason of achieving “Reserva” status, and hence a higher price.

A better value wine, with say, only 10 months in barrel (and therefore not eligible for “Crianza” status), may actually be a higher quality wine as 10 months was the optimum time for the balance of oak and fruit aromas that the winemaker was looking for.

The other issue with this focus on oak aging is that it can also overshadow the other critical and fundamental winemaking factors such as the location of the vineyard, “terroir” and the aging process in general – which rings especially true when shorter barrel aging is preferred following wetter seasons, for example.

In summary, all reputable cellars will age their wine appropriately, and a well-made wine might not even use the standard Spanish classification.

Coming next. How to choose a good bottle of Spanish wine in a supermarket?


Always a highlight of our trip!

Spanish wine tour reviews

This was the second time we did a wine tour with Tannin Trails during our time in the Costa Del Sol, and it is was once again a highlight of our trip here. Kelly and Vanessa do an amazing job picking wonderful local wineries and experiences! This year we loved visiting 2 fantastic wineries (different from the previous year and with wonderful wine, views, and staff) and doing a local cooking class in Ronda where we learned how to make some wonderful Spanish dishes!