Brix : Acid & Harvest at the Right Maturity

The Brix : acid ratio (also written SSC:TA, soluble-solids to titratable-acidity) is the soluble-solids reading in °Brix divided by the titratable acidity expressed as a percentage. It is the single most useful chemical maturity index for many fruits because it captures the sugar–acid balance that drives eating quality: a table grape at 18°Brix with 0.6% tartaric acid has a ratio of 30:1, comfortably inside its 20–30:1 optimal window.

It is ready when three indices are all met for your purpose: the soluble solids clear the commodity's minimum Brix, the titratable acidity is at or below the maximum, and the Brix : acid ratio sits inside the optimal window. If the Brix is too low or the ratio is below the window the fruit is immature; if the ratio is above the window the acid has dropped too far and the fruit is over-mature. The tool returns an immature / optimal / over-mature verdict and a harvest-now-vs-wait call.

The Codex standard for table grapes is a minimum of 16°Brix or a Brix : acid ratio of at least 20:1 (some regions accept 17:1). The optimal eating-quality window is roughly 20–30:1. Grapes do not sweeten after picking — they have no starch reserve — so they must be picked at full maturity; the tool flags grapes below the window as immature with a clear wait recommendation.

Citrus uses a minimum Brix and, critically, a minimum Brix : acid ratio — commonly around 8:1 for oranges and 6:1 to 7:1 for grapefruit — because citrus does not sweeten off the tree. An orange at 11°Brix and 1.0% citric acid is at 11:1, above the 8:1 floor and inside the optimal band, so it is mature. Below the ratio floor or above the acidity ceiling the fruit is legally immature and tastes sharp.

Storage and long-haul shipping pick a touch earlier — firmer and slightly more acid — so the fruit arrives at peak rather than over-ripe. The tool shifts the standard for the storage purpose: it raises the minimum Brix a little and lowers the optimal ratio band (because more retained acid means a lower ratio), so a sample that reads 'optimal' for market may read 'harvest for market now, too ripe to store' under the storage setting.

It depends on whether the fruit is climacteric. Climacteric fruit (mango, apple, pear, peach, tomato, kiwifruit) continue to ripen and soften off the plant — they are picked mature-green and firm for storage and ripened later. Non-climacteric fruit (grape, citrus, pomegranate, strawberry, melon) do not gain sugar after picking, so they must reach full maturity on the plant. The tool's notes flag which fruits will not improve once detached.

For apple, pear, peach, mango and kiwifruit, flesh firmness measured with a penetrometer is a primary harvest index alongside Brix. Firmer than the harvest ceiling means the fruit is still immature; softer means it is advancing toward eating-ripe. Pick firmer (nearer the ceiling) for controlled-atmosphere or long-haul storage so the fruit still has firmness to spend in transit. The tool adds a firmness check when you supply a reading for these fruits.

Squeeze juice from a representative sample and read the soluble solids on a refractometer (°Brix). Measure titratable acidity by titrating the juice to pH 8.2 with sodium hydroxide and express it as the percentage of the fruit's dominant acid — tartaric for grapes, citric for citrus and many others, malic for apple, pear and peach. Optionally measure flesh firmness with a penetrometer for the fruits where firmness is an index.

Over-mature means the Brix : acid ratio has climbed above the optimal window, almost always because acidity has fallen rather than because sugar rose. The fruit tastes flat and bland and stores poorly. The tool flags it and recommends harvesting immediately for quick sale rather than storage, and bringing forward the next picks so the rest of the block is not left too long.

Yes — Brix alone is not enough. A fruit can carry enough sugar yet still be below the ratio window because its acidity is too high, which reads as immature and sharp. That is exactly why the index uses the ratio, not just Brix: the tool checks the minimum Brix, the maximum acidity and the ratio together, so high-Brix-high-acid fruit is correctly called immature rather than ready.

They are widely-cited planning standards drawn from UC-Davis postharvest maturity indices, the Kader Postharvest Technology textbook (UC ANR 3311), Codex commodity standards and USDA grade standards. Real targets vary with cultivar, growing region and end market, and quarantine or buyer specifications may differ. Treat the verdict as a strong default and confirm against the specification your fruit must meet.

Brix : acid ratio = soluble solids (°Brix) ÷ titratable acidity (%). The fruit is optimal when Brix ≥ the commodity minimum AND acidity ≤ the commodity maximum AND the ratio is within [ratioLo, ratioHi]. Below the ratio floor or below minimum Brix is immature; above the ratio ceiling is over-mature. For the storage purpose the minimum Brix is raised and the ratio band shifted lower so fruit is picked slightly earlier.

No. The calculation runs entirely in your browser using the built-in commodity harvest-index table and the Brix : acid formula. Nothing you enter is sent anywhere.