In the vineyard

Harvest and Brix: how ripeness is measured, and who decides

In most wine regions the picking date is the winemaker's judgement. In Ontario it is partly a legal question, because the regulation sets a minimum sugar for every variety and a second, higher one for any wine that names a place.

What Brix actually measures

One degree Brix is one gram of sucrose per hundred grams of solution. In practice it is a proxy: the instrument reads dissolved solids, and in ripe grape juice those are overwhelmingly sugars, so the number stands in for sugar concentration and therefore for the alcohol the wine can reach. Roughly speaking, Brix multiplied by about 0.55 to 0.6 gives potential alcohol by volume, which is why an 18.0° picking decision and a 20.0° one produce noticeably different wines.

Growers measure it in the field with a handheld refractometer — a drop of juice on a prism, read against a scale — and wineries confirm it at the weighbridge with a hydrometer or a bench refractometer. The field reading guides the decision; the delivery reading determines what is paid and what the fruit is legally allowed to become.

The two-tier rule

Appendix A of Ontario Regulation 406/00 sets a minimum average Brix for each named variety in two columns: one for wine carrying the provincial designation, a higher one for wine claiming a viticultural area, estate bottling or a single vineyard. Chardonnay is 18.0° and 20.0°; Merlot 19.0° and 20.5°, the highest figure in the table; Riesling is 17.0° and 17.0°, one of four entries that does not rise at all. Varieties without a named line fall into a residual category at 17.0° and 18.0°.

The consequence for a grower is concrete. A block that reaches 19.0° in a cool autumn can be sold as Ontario Merlot but not as Four Mile Creek Merlot, and the difference in what the wine can be called is a difference in what it is worth. That is why the last fortnight before picking involves so much sampling: the decision is not only about flavour but about which side of a legal threshold the fruit lands on.

Sampling, and why it is harder than it sounds

A vineyard does not ripen evenly. Berries on the outside of a cluster differ from those inside it, clusters on the shaded side of the canopy differ from the exposed side, vines at the end of a row exposed to more light and wind differ from those in the middle, and a low corner of a block can run a degree behind the rest. A single refractometer reading from a convenient cluster is close to meaningless.

The working method is a systematic walk: berries taken from many vines across the block, from both sides of the canopy and from different positions on the cluster, crushed together and read as one sample. The number that matters legally is a minimum average, which is what that composite is estimating. Acid and pH are tracked alongside, because ripeness is not a single axis — sugar climbs while acid falls, and the picking decision is usually a judgement about where those two curves cross rather than about sugar alone.

The exception: frozen fruit

For icewine the rules become far stricter and stop being about variety at all. The wine must be made from vinifera listed in Table 1 of Appendix B or from the hybrid Vidal — no other hybrid qualifies. The grapes must be naturally frozen on the vine and picked while the air temperature is minus 8°C or lower, then pressed immediately in a continuous process.

The Brix bar is 32.0° at the press and a 35.0° average in the final blend, against 17.0° to 20.5° for table wine. The regulation also closes the obvious shortcuts: fruit may be artificially refrigerated only to a temperature not below minus 4°C, and no freeze concentration of juice, must or wine is permitted. The cold has to be real and it has to happen in the vineyard.

What the grower is paid on

Brix is not only a legal threshold; it is part of the commercial settlement. The 2026 Grape Growers of Ontario price schedule notes that icewine and late harvest grapes are exempt from brix testing at normal harvest and are paid at the varietal base price plus 129 per cent — the premium that compensates for hanging a crop into January and risking losing it. Grapes destined for sparkling wine are paid at the varietal base price. The vine year page covers the season that leads up to all of this, and the statistics page explains how provincial tonnage figures are assembled from these deliveries.