Why is my fudge grainy, or too soft to cut?

Fudge is a sugar syrup that has been persuaded to crystallise into crystals so small the tongue cannot feel them. Two things decide the outcome: the temperature you boil to, which sets how much water is left and therefore how firm the fudge will be, and when you start agitating it, which sets how big the crystals grow. Beating a hot syrup gives a few large crystals and a gritty texture; beating a cooled one gives many tiny ones and a smooth fudge. Everything else is detail.

Safety

What you'll need

• A sugar thermometer or digital probe
• A heavy-based deep pan
• A lined shallow tin
• A pastry brush and a cup of water (optional)

Step by step

1. Dissolve the sugar completely before it boils.Over a low heat, stirring, until you cannot feel any grittiness on the spoon against the pan base. Any sugar crystal that survives into the boil becomes a seed that starts coarse crystallisation later.
2. Wash down the pan sides.Brush the inside of the pan just above the syrup with a wet pastry brush to dissolve any splashed crystals, or put a lid on for two minutes so the condensation does it. One stray crystal is enough to make grainy fudge.
3. Stop stirring once it boils.From the boil onwards, leave it alone. Stirring a boiling syrup encourages crystals to form and to grow large. Swirl the pan gently if you must move it.
4. Boil to 114–116°C and check the thermometer.This is the soft-ball stage and it decides the final firmness. A couple of degrees low gives fudge that will not set; a couple high gives something closer to tablet. Test the thermometer in boiling water first — it should read 100°C at sea level.
5. Cool undisturbed to about 43°C.Take the pan off, stand it somewhere safe and do not touch it. Adding butter and vanilla on top without stirring at this point is fine. You are waiting for the syrup to become supersaturated and cool enough that crystals form small.
6. Then beat, hard, until it thickens and dulls.A wooden spoon or an electric mixer. The mixture loses its gloss, lightens slightly and thickens — that is the crystallisation happening. Pour into the lined tin the moment it does, because it sets fast.
7. Cool completely before cutting.In the tin, at room temperature, for several hours. Mark it into squares while still slightly warm and cut when fully cold.

Tips

• Condensed milk fudge recipes avoid nearly all of this — they use a much shorter boil and set on the milk solids rather than on controlled crystallisation. They are a genuinely reliable alternative.
• Humid days give softer fudge because sugar draws water from the air. Boil a degree higher in muggy weather.
• Glucose syrup or a spoon of golden syrup interferes with crystal growth and makes smooth fudge much easier to achieve.
• A digital probe is far better than a clip-on glass thermometer for this — it responds faster and you can see the display without leaning over the pan.

Common mistakes

• Stirring the syrup while it boils — It is the single most reliable way to make grainy fudge. Once dissolved and boiling, the spoon stays out.
• Beating it while it is still hot — Hot syrup grows a few large crystals. The whole point of the cooling wait is to force many small ones.

If it doesn't work