tags: [] - coffee/roasting - coffee/roasting/profile aliases: - TP - Turnaround point - Bean temperature minimum

Turning Point¶

Tags: #coffee/roasting #coffee/roasting/profile Aliases: TP, Turnaround point, Bean temperature minimum Related: Roasting MOC | Charge Temperature | Rate of Rise | Roast Profile | Development Time Ratio Status: ✅ Complete

Overview¶

The turning point (TP) is the moment during a coffee roast when the bean temperature probe registers its lowest reading — the point at which the beans stop absorbing heat faster than the environment can supply it and the temperature curve turns upward. It marks the end of the initial heat-absorption phase and the beginning of the sustained temperature rise through drying, browning, and development. The turning point's temperature, timing, and the Rate of Rise (RoR) immediately following it are important diagnostic data points that reflect the quality of the charge temperature setting and the opening energy environment of the roast.

What Causes the Turning Point¶

When cold green beans are charged into a hot drum, they immediately absorb heat from the drum metal, the hot air, and radiation from the burner system. For the first 60–90 seconds of a typical roast, the heat the beans absorb is greater than what the air temperature probe registers as incoming, so the bean temperature reading — measured by a probe inserted into the bean mass — drops. This drop reflects the cooling effect of the beans on their immediate environment, not a true fall in drum temperature.

Once the beans have absorbed enough initial heat and the drum's thermal energy begins to transfer efficiently into the bean mass, the rate of heat loss from the beans equals, then is exceeded by, the rate of heat input, and the curve reverses direction upward. The lowest point of this curve is the turning point.

Turning Point Parameters¶

The turning point has three measurable characteristics:

Parameter	Typical Range	Significance
Temperature at TP	65–100 °C	Reflects charge temperature and batch mass; lower TP = more energy in opening
Time to TP	45–120 seconds	Faster TP = more aggressive charge; slower TP = softer opening
RoR at TP	The slope of the curve as it begins rising	Steep early RoR = high charge temp; flat early RoR = low charge temp

These parameters are strongly influenced by charge temperature: a high charge temperature produces a shallow TP (the beans don't cool as far before turning) and a rapid, steep early Rate of Rise; a low charge temperature produces a deeper TP and a gentler initial RoR. Batch size also affects TP — a larger bean mass absorbs more heat and generally produces a deeper, later turning point.

Turning Point and Profile Consistency¶

Because the turning point is directly downstream of the charge temperature, inconsistent charge temperatures produce inconsistent turning points. A shift of 5 °C in charge temperature can move the TP temperature by 3–7 °C and alter its timing by 10–20 seconds, changing the early RoR curve and cascading through first crack timing and development phase.

Roasters using data logging software (Cropster, Artisan) record TP temperature and time for every batch, alongside charge temperature, as primary consistency metrics. Significant deviation in TP parameters between batches using the same green coffee and target profile signals a charge temperature error, a changed batch size, or a difference in bean moisture or density.

Relationship to Rate of Rise¶

The turning point is the zero-crossing of the Rate of Rise curve — the moment when RoR transitions from negative (bean temperature falling) to positive (bean temperature rising). The steepness of the RoR curve immediately after the TP determines how aggressively the roast opens. In a well-managed profile, RoR rises steeply off the TP, peaks before the drying phase completes, and then declines smoothly through browning and into development. A flat or sluggish RoR off the TP may indicate insufficient charge energy and risk an extended drying phase. An excessively steep RoR may indicate over-charging and risk scorching.

Key Facts¶

The turning point is the lowest bean temperature reading in the roast — the moment the curve reverses from falling to rising
Caused by the initial heat-absorption effect of cold beans entering a hot drum
Typically occurs 45–120 seconds after charge at 65–100 °C (highly roaster- and batch-size-specific)
Turning point temperature and timing are direct outputs of charge temperature and batch mass
Inconsistent TP parameters indicate inconsistent charge conditions
Recorded by all major roast logging software as a primary consistency metric

References¶

Changelog¶

Date	Change
2026-04-27	Note created

This article is part of All-About-Coffee.com - The comprehensive coffee knowledgebase.