Grape Varieties - An Overview

When talking about wine we are specifically talking about wine made from grapes – wines made from other fruits such as plum, apple and apricot for example are known as fruit wines. (Very inventive I know.)

Wine Grapes VS Table Grapes

It’s important to note there is a big difference between table grapes that we munch on from the supermarket and the grapes we use to make wine.

The main differences are the species of grape variety – Vitis Vinifera (wine) and Vitis Labrusca (Table), and Vitis Rotundifolia/ Muscadine (Table) and some Vitis Vinifera (Table – these will be the premium supermarket grapes).

Wine grapes have thicker skins which is where all those lovely tannins and that pretty colour come from, whilst table grapes are thinner skinned so they are nicer to munch on and give that lovely juicy pop when you crush them in your mouth.

The reverse of what you’d expect is true when it comes to sweetness. Wine grapes have about twice the sugar levels of table grapes and they are harvested at around 22-30% sugar while table grapes will be closer to 10-15%. The lower sugar makes them lighter for snacking but not suitable for fermentation.

Wine grapes tend to be smaller and have more intense flavours which is exactly what you want when making wine. Table grapes are larger, bursting with juice from being more swollen with water which makes them more refreshing.

Yields, which is a major factor when looking at the quality of the wine being produced are also much smaller in wine grapes, table grapes are trellised so the grapes hang independently of each other allowing for much higher yields which means all the flavour is spread out among a greater number of grapes so less intensity of character.

So why do we use Grapes to make wine?

There are many reasons for this, sugar content, acidity, tannins – but I’m not going to focus on that for now.

I’m actually talking more about the flavours we find in grapes which make them so perfect for making wines.

Each grape variety is associated with different flavour categories, but where do these flavours come from...? Is there some kind of mad scientist in the winery tipping apples, lemons and peaches into the wine to add those flavours?

As much fun as that image is it's sadly not how it works. All the flavours in a wine come from the grape varieties, the techniques used to make them as well as flavours that develop during the ageing process.

If not a mad scientist where does the flavour come from?

It's all down to nature and organic chemistry, if you think of flavour as an organic compound, these compounds are found in all manner of different plants and fruits, but whilst they are present in other fruits they are found in grapes in abundance. The grapes themselves don’t taste of all of these flavours if you eat them from the vine but during fermentation, these volatile compounds are released and can then be detected by our olfactory system (smell).

Common Compounds (see links for the mad science bit)

Aldehydes

Acetaldehyde: Think bright green apple like a Granny Smith

Benzaldehyde: Bitter almond or marzipan which can be found in some aged Pinot Gris, Sherry and Champagne.

Furfural: Flavours of dried and burnt wood, caramel and almond, this flavour often appears in oak-aged wines.

Hexanal and hexenal: These aldehydes give us the scents of freshly cut grass and tomato leaf which can be found in some Sauvignon Blanc.

Vanillin: It tastes exactly what it sounds like and gives the flavour of vanilla bean. In wine, it comes from the use of oak during fermentation and/or ageing. American oak (Quercus alba) gives more vanillin character than French oak (Quercus robur),

Esters

Esters are volatile flavour compounds created during fermentation. Esters are responsible for some of the primary fruit flavours we get in young wines.

Butyl acetate: This ester smells of red apples.

Isoamyl acetate and ethyl acetate: Banana and pear respectively.

Octyl acetate: Bright aromas of citrus fruit.

Ketones and diketones

Beta-damascenone: Floral blossom aromas and soft red fruit such as strawberry.

Beta-ionone: The heady aroma of violet in some Pinot Noir and Syrah.

Diacetyl: Think butter, popcorn (when oaked) and butterscotch. Diacetyl is a by-product of fermentation and malolactic fermentation where bacteria convert malic acid (found in green apple) in wine to a softer lactic acid (dairy). Think of those Chardonnays you either love or love to hate (ABC – the buttery note and the coconut note below are among the main reasons people hate Chardonnay).

Lactones

Octalactone: Coconut. Another one we associate with American Oak

Sotolon: Spice, nuts, toast or maple syrup. This is associated with botrytised (noble rot) wines like Sauternes, Tokaji, TBA, and other aged wines such as Madeira.

Mercaptans

These volatile sulphur compounds occur in grapes and are released by fermentation. These are the pleasant ones see below for the less enjoyable sulphur compounds.

3MHA (3-mercaptohexyl acetate): Guava and gooseberry aromas – in those punchy NZ Sauvignon Blancs.

3MH (3-mercaptohexan-1-ol): Passion fruit - as above so below

4MMP (4-mercapto-4-methylpentan-2-one): Blackcurrant leaf, blackcurrant or cassis – synonymous with Cabernet Sauvignon.

Phenols are derived from oak ageing:

Eugenol: Clove (which can also be created by yeast if the fermentation runs to hot).

Guaiacol: Smoky, toast and roasted aromas to wines.

Pyrazines

Methoxypyrazines: Herbaceous notes and green bell pepper which we see in some Cabernet Sauvignon and Sauvignon Blancs (yes, they are related Cab Sav comes from Cab Franc X (crossed with) Sauvignon Blanc)

As well as in Carménère (also related to Cab Franc in a fairly incestuous way).

This can come from underripe grapes (deliberately) just like most green peppers are unripened red peppers.

Terpenes

These reside primarily in grape skins and are all around in nature: in flowers, fruits and the leaves of plants.

Terpenes make wines such as Muscat and Gewürztraminer all that they are – fragrant and floral as well as giving the citrus character to Riesling.

Geraniol: Rose petals, Turkish delight. (Again, not my thing – difficult when your wife is Bulgarian)

Hotrienol: Linden blossom (something few people will know) but is also part of the elderflower smell we find in Sauvignon Blanc.

Linalool: Think lavender, white blossom and lilies (I’ve always hated Lilies, the smell is so strong and they dye your clothes if you get anywhere near them – luckily, we have cats so no more lilies in our house).

Limonene and citral: Citrus peel.

Nerol and citronellol: Floral, citrusy scents

Rotundone: Think peppercorns – flavours commonly found in Shiraz, Syrah and Grüner Veltliner

1,8-cineole: Eucalyptus which we see in Coonawarra Cab Sav.

Alpha-pinene: Think of the piney resinous note from juniper and rosemary.  Garrigue scrubland flavours that we find in the red wine from Southern France.

Both of the above are dispersed by the wind and are volatile aroma compounds that can attach to the bloom on the skin of grapes adding their flavours to the wine.

It hurts my brain to try and pronounce this one

1,1,6-trimethyl-1,2-dihydronaphthalene (sorry about that) otherwise (always) known as TDN gives us the infamous petrol or kerosene aroma in aged Riesling and comes from sun-exposure in the grape skins.

Note there is some cross over with the compounds and the aromas that they give to a wine, so it’s not always possible to identify exactly where the toast note comes from for example.

Not all the flavours are pleasant

Yeast is responsible for making some fairly horrible flavours as well – most of these will never come through to the final wine but occasionally when you open a bottle you will get some sulphur character.

These can either be from the sulphur that can be sprayed onto grapes to stop mildew from forming which then takes the place of oxygen in the hydroxyl group of alcohol to create Thiols during fermentation. Most of the time they will stop spraying before harvest so this doesn’t happen. Sulphites can also be added to wines to act as a preservative to stop them from going off.

This can show in a variety of ways:

Ethyl-Mercaptan: Burnt Rubber

Hydrogen Sulphide: Rotten Egg

Methyl Mercaptan: Cabbage

Hydrogen Sulphide: Burnt Match

This can be known as Bottle stink and the unpleasant flavours can dissipate if the wine is left open for a short period of time. You can also wash a copper penny and drop it into your glass according to Jeff Potter in his book Cooking for Geeks as this will bond with the thiols, resulting in odourless, harmless copper-sulphide crystals.

Wine Making Techniques

We also get other flavours in our wines but these come more from the fermentation and the winemaking techniques.

Personal taste

Taste and experience also play a part in how we taste and pick out flavours – feel free to explore that in the following post.