Wine · Winemaking & Styles · Study guide
The Grape
A study guide to the grape as winemaking's raw material — what the pulp, skins, seeds, stems and bloom each contribute, where sugar, acid, colour and tannin live, and how red and white winemaking use them differently.
Every wine begins as a single thing: a grape berry. And that berry is not a uniform ball of juice — it's a little package of parts, each holding something different that the winemaker may want, or want to avoid. Sugar and acid in the juicy pulp; colour, flavour and tannin in the skins; more tannin in the seeds and stems; wild yeast dusted on the outside. What a wine becomes depends on which of those parts the winemaker draws on, and how much.
The framing idea: wine is grape juice plus whatever you choose to take from the rest of the berry. A white wine is mostly the pulp's juice, made while keeping the skins and seeds at arm's length; a red wine is the whole berry, deliberately steeped to pull colour and tannin from the skins. Learn where each component lives, and the difference between a pale, crisp white and a black, structured red becomes a map of the berry. (Part of the Winemaking & Styles library; for the whole living plant see anatomy of the vine.)
The one thing to fix first: the whole toolkit is in the berry
Before any cellar technique, everything a winemaker has to work with is already inside the grape: the sugar that becomes alcohol, the acid that gives freshness, the pigments that give colour, the tannins that give structure, and the flavours. Winemaking is largely the art of choosing which parts to extract and which to leave behind. Fix that, and pressing, maceration and the rest stop being a list of tricks and become decisions about the berry.
The parts of the berry, and what each gives
The memorise-cold table:
| Part | What it holds | What it gives the wine |
|---|---|---|
| Pulp / flesh | Water, sugar, acid (tartaric primary, malic secondary) | The juice — sugar → alcohol; acid → freshness. Nearly colourless in almost all grapes |
| Skins | Colour pigments, tannin, most flavour | Everything that makes a wine red and structured |
| Seeds / pips | Tannin (harsh), bitter oils | Hard tannin — but crush them and you get bitterness |
| Stems / stalks | Tannin | Extra tannin — only wanted when fully ripe |
| Bloom / cutin | Waxy coat carrying wild yeast | The natural yeast supply; also limits moisture loss on the vine |
Key facts
| The juice | From the pulp — sugar, water and acid; almost always colourless |
| Main acids | Tartaric (primary) and malic (secondary) |
| Colour & flavour | Live in the skins — extracted only by contact |
| Tannin's homes | Skins, seeds, stems — plus oak in the cellar |
| The yeast | Wild yeast in the bloom on the skin |
| Red vs white | Red uses the whole berry; white mostly the juice |
The vocabulary you'll actually meet
- Must — crushed grapes (juice plus skins, seeds, sometimes stems) before or during fermentation.
- Free-run juice — the juice that flows from gentle crushing, before hard pressing.
- Bloom — the natural waxy, yeast-bearing dust on a grape's skin.
- Tannin — the drying, grippy compound from skins, seeds, stems (and oak) that gives red wine its structure.
In this guide
- The berry, part by part — what each contributes and what to avoid
- The berry part → glass table
- Where tannin comes from — the three homes, plus oak
- Red vs white: using the whole berry, or just the juice
- Classic exam questions
The berry, part by part
- Pulp (flesh). The juicy middle, and the bulk of the berry: water, sugar and acid. Its sugar is what yeast turns into alcohol; its acidity (mostly tartaric, with malic secondary) gives the wine freshness and ageing spine. Crucially, in almost every grape — even black ones — the pulp and its juice are nearly colourless, which is why a red grape can make a white wine.
- Skins. The prize for red wine: the skins carry the colour pigments (anthocyanins), a large share of the flavour, and much of the tannin. Nothing red or structured reaches the wine unless the winemaker gives the juice contact with the skins.
- Seeds (pips). A source of tannin — but harsh tannin, plus bitter oils. Useful in moderation, dangerous if abused: crushing the pips releases bitterness, so gentle handling aims to keep them intact.
- Stems (stalks). Also tannic. They're only an asset when fully ripe (brown and woody); green, unripe stems taste stalky, so most winemaking removes them.
- Bloom (cutin). The waxy coating on the skin, which carries naturally occurring wild yeasts and helps the berry retain moisture on the vine. It's the reason grapes can ferment with no added yeast at all.
Berry part → glass
| Part used | What it adds | Where it matters |
|---|---|---|
| Pulp juice | Alcohol (from sugar) and acidity | Every wine — the base |
| Skins | Colour, flavour, tannin | Reds; skin-contact whites |
| Seeds | Harsh tannin, bitterness (if crushed) | Kept intact to avoid |
| Ripe stems | Fine tannin, perfume | Whole-bunch reds |
| Bloom yeast | Spontaneous fermentation | Wild/natural winemaking |
Where tannin comes from
Tannin — the compound that dries the mouth and gives red wine its grip and ageing potential — has three homes in the grape: skins, seeds and stems, and it accumulates before the grape changes colour at véraison. A fourth source is added later in the cellar: oak. That map is the whole reason red winemaking is built around controlling extraction from the skins (and avoiding harsh seed tannin) — the subject of the red winemaking guide.
Red vs white: whole berry, or just the juice
The single biggest fork in winemaking is how much of the berry you use:
- Red wine uses the whole berry, fermenting the juice on its skins (and seeds) to extract colour, flavour and tannin — because everything that makes a wine red lives in the skins, not the pale juice.
- White wine mostly uses the juice alone: the grapes are pressed and the juice run off the skins before fermentation, to keep the wine pale, fresh and low in tannin (the white winemaking guide covers the protective handling this needs).
So a black grape can make a white wine (press gently, take only the colourless juice), and the decision — whole berry or just the juice — matters as much as the grape variety itself.
Classic exam questions
- Where do sugar and acid live in the grape? — In the pulp (flesh); the main acids are tartaric (primary) and malic (secondary).
- Why can a black grape make a white wine? — Because the pulp/juice is colourless; the colour is only in the skins.
- What do the skins contribute? — Colour, flavour and tannin — the makings of red wine.
- Why avoid crushing the seeds? — They release bitter oils and harsh tannin.
- When are stems useful? — Only when fully ripe, for fine tannin (whole-bunch reds).
- What is the bloom, and why does it matter? — The waxy skin coating carrying wild yeast, enabling spontaneous fermentation.
- Name tannin's sources. — Skins, seeds and stems of the grape, plus oak in the cellar.
The grape holds the whole recipe; winemaking is mostly the choice of which parts to use — take just the juice for a white, the whole berry for a red, and the wine follows from the berry.