What is grape must?

Quick answer: what is grape must?

Grape must is the grape-derived material from which wine is made, before it becomes finished wine.

In formal oenological terminology, grape must is the liquid obtained from fresh grapes through processes such as crushing, destemming, draining or pressing. In everyday winery language, however, “must” often means the juice together with some or all of the grape solids still in contact with it. Those solids may include skins, seeds, pulp and, depending on how the grapes were handled, stems.

Must can be unfermented, beginning fermentation or actively fermenting. During alcoholic fermentation, yeast consumes the grape sugars and produces alcohol and carbon dioxide. That transformation changes must into wine.

The important idea is that must sits between grapes and wine. It is the material being prepared for, or undergoing, fermentation.

Where does must fit into winemaking?

The sequence is straightforward:

1. Grapes are harvested and brought to the winery.
2. Crushing, destemming, draining or pressing releases grape liquid.
3. The extracted material is called must.
4. The must may be held, settled or left in contact with grape solids.
5. Yeast carries out alcoholic fermentation.
6. The resulting wine is separated from solids where necessary, then clarified and matured.

The material called must can look very different depending on this handling. Pressed juice that has been separated from skins and seeds may be relatively clear. Crushed grapes fermenting with their skins and seeds can be thick, coloured and full of suspended solids.

This is why there is no single universal “recipe” for must.

Must, grape juice and wine: what is the difference?

Must and grape juice

Grape juice emphasises the liquid part of the grape. It can refer to juice intended for drinking, or to grape liquid prepared for fermentation.

Must is a broader winemaking term in practical use. It may mean the juice alone, but it can also mean juice still carrying or touching skins, seeds, pulp or stems.

So, grape juice can be part of must, but “must” tells you more about its place in the winemaking process than its appearance. It does not necessarily mean a clear liquid.

Must and fermenting must

“Fermenting must” simply means must in which alcoholic fermentation is under way. It is a useful process description rather than a completely separate substance.

Winemakers may continue to call the material must while fermentation is active, even as it is beginning to develop into wine. There is not necessarily one universal moment when everyone stops using the word “must”.

Must and wine

Wine is the product of partial or complete alcoholic fermentation of grapes or grape must. In simple terms, must is the grape material awaiting or undergoing fermentation; wine is the fermented beverage that results.

Must is also different from pomace or marc. Pomace or marc is the solid residue left after extraction, made up mainly of skins, seeds and sometimes stems.

What can grape must contain?

Must may contain:

• grape juice;
• skins;
• seeds;
• pulp;
• suspended grape particles; and
• sometimes stems.

The word “may” matters. Stems are removed in destemming, while whole-bunch or whole-cluster handling can leave some or many stems with the grapes. Pressing can also separate much of the solid material from the liquid.

The composition changes with grape variety, ripeness and physical handling. Crushing, pressing, destemming and skin contact all produce different forms of must.

Why does must composition matter?

Sugar

Grape sugars provide the starting material for alcoholic fermentation. Yeast converts those sugars into alcohol and carbon dioxide. The amount of sugar in must therefore helps determine how fermentation progresses and the potential alcohol of the resulting wine.

Acidity and pH

Acidity and pH influence the environment in which fermentation occurs. They also affect stability, microbial activity and aspects of wine colour and freshness.

For a wine drinker, this helps explain why the same basic grape material can lead to wines that feel crisp, soft, firm or rounded. Must chemistry is one part of that outcome.

Skins and seeds

Skins can contribute colour, flavour compounds and phenolic material. Seeds also contain phenolic compounds, including tannins. Contact between juice and these solids can influence the finished wine’s colour, texture, flavour and sense of structure.

That contact is not automatically better or worse. It is a winemaking choice shaped by the desired style.

Stems

Stems are not an essential part of every must. When they are retained, they can change the material’s phenolic character and contribute a different style of extraction. Destemming removes them and can reduce the possibility of stem-derived tannin, astringency or green character.

How do red, white and rosé wines handle must?

Red wine

Red grapes are commonly crushed and fermented with their skins and seeds. This gives the juice time to extract colour, flavour and tannin from the solids. Some red-wine methods also retain stems, while others remove them.

The important point is that red-wine must commonly remains in contact with solids during fermentation, but the exact approach varies.

White wine

Many white-wine processes press the grapes and separate the juice from most skins and seeds before fermentation. This creates a lighter-coloured liquid with less solid contact.

There are exceptions. Skin-contact white and amber wines may ferment with white-grape skins, seeds and sometimes stems. White grapes do not automatically produce a clear, solids-free must.

Rosé wine

Rosé production varies. It may involve direct pressing or a limited period of contact between red grape juice and skins. Managing that contact helps control colour and phenolic extraction.

There is no single universal rosé method, so “rosé must” should be understood as a process description rather than a fixed substance.

How Australians may encounter the word “must”

Australian wine-industry, winery, research and educational material commonly uses “must” as a production term. Australian readers may see it used for extracted grape liquid, or for juice still carrying skins and seeds in contexts such as red-wine fermentation.

It is best read in context. The word does not, on the evidence used here, need to be treated as mandatory or standard wording on Australian consumer wine labels.

In brief

Grape must is the material made from fresh grapes that is destined to become wine. Formally, it is the liquid extracted by crushing, destemming, draining or pressing. In practical winemaking language, it often includes that liquid together with grape solids.

Once yeast ferments its sugars, must becomes wine. Whether the must contains skins, seeds, pulp or stems—and how long they remain in contact with the liquid—helps shape the wine’s colour, flavour and texture.

For a broader overview of the production sequence, see How wine is made.

Frequently asked questions

Is grape must the same as grape juice?

Not always. Grape juice refers mainly to the liquid fraction, while must can mean the liquid together with grape solids. In some contexts the terms overlap.

Is must always unfermented?

No. Must may be unfermented, beginning fermentation or actively fermenting. “Fermenting must” describes must while yeast activity is under way.

Does must contain skins and seeds?

It may. Red-wine must commonly contains or remains in contact with skins and seeds, while many white-wine processes separate the juice from them before fermentation.

Are stems always part of must?

No. Stems may be removed by destemming or retained through whole-bunch handling. They should be treated as a possible, not universal, component.

What does must become?

During alcoholic fermentation, yeast converts the sugars in must into alcohol and carbon dioxide. The fermented product is wine.