tags: [] - coffee/roasting - coffee/roasting/profile aliases: - Charge temp - Drop-in temperature - Roast charge temperature

Charge Temperature¶

Tags: #coffee/roasting #coffee/roasting/profile Aliases: Charge temp, Drop-in temperature, Roast charge temperature Related: Roasting MOC | Rate of Rise | Development Time Ratio | Roast Profile | Turning Point Status: ✅ Complete

Overview¶

Charge temperature is the drum temperature at which green coffee beans are loaded (charged) into the roasting drum at the start of a roast. It is the first deliberate variable a roaster sets before a batch begins and has a cascading effect on the entire roast trajectory — determining the initial rate of heat transfer to the beans, the depth and speed of the turning point (the lowest bean temperature before the curve begins rising), and the overall shape of the rate of rise curve through the rest of the roast. Charge temperature is not a universal fixed value; it varies by roaster model, batch size, bean density, moisture content, and desired roast profile. Setting the correct charge temperature is foundational to producing repeatable, consistent roast profiles across batches.

What Charge Temperature Controls¶

When green beans enter a hot drum, they immediately absorb heat from the drum surfaces and the heated air inside. The rate of initial heat transfer is proportional to the temperature differential between the beans (typically at room temperature, 15–25 °C) and the drum environment. A higher charge temperature creates a larger differential and a more aggressive initial heat transfer; a lower charge temperature reduces the rate of early heating.

This initial heat input directly sets:

The Turning Point temperature and timing: A high charge temperature produces a shallow, rapid turning point (the bean temperature minimum after charging); a low charge temperature produces a deeper, slower turning point
The early Rate of Rise: A more aggressive opening sets a higher early RoR, which must then be managed downward through the roast to achieve a smoothly declining curve
Total roast time: Higher charge temperatures tend to produce shorter total roast times; lower charge temperatures lengthen the roast, extending drying phase and total heat exposure

Setting Charge Temperature¶

There is no single correct charge temperature for all situations. Typical ranges for drum roasters with standard batch sizes are 180–230 °C, but these figures are highly roaster-specific. A charge temperature of 200 °C on a 12 kg Probat drum roaster is a fundamentally different thermal environment from 200 °C on a 1 kg sample roaster.

Factors that inform charge temperature selection:

Factor	Effect on Charge Temperature
Batch size	Larger batches require higher charge temperatures; more bean mass absorbs more heat
Bean density	Denser, higher-altitude beans conduct heat more slowly; benefit from slightly higher charge temperatures
Green moisture content	Higher-moisture green coffee requires more energy to drive off moisture; slightly higher charge temperatures can compensate
Desired total roast time	Shorter target roast time → higher charge temperature; longer target → lower
Previous batch (consecutive batches)	Drum retains residual heat; charge temperature for the second batch may need to be reduced vs the first
Ambient temperature and humidity	Cold weather or high humidity reduces drum heat retention; charge temperature may need adjustment

Charge Temperature and Roast Defects¶

Incorrect charge temperature is a primary cause of two common roast defects:

Too high a charge temperature → Scorching or Tipping

When green beans contact an excessively hot drum, the outer surface of the bean heats far more rapidly than the interior. The result is scorching — dark spots on bean surfaces from localised overheating — or tipping — darkened, shrunken bean tips caused by radiant heat concentration at the bean's ends. Both defects contribute harsh, acrid, or smoky notes to the cup.

Too low a charge temperature → Extended drying; potential baking

An insufficient charge temperature means the beans absorb heat too slowly in the early drying phase. This extends the total roast time in ways that are difficult to correct mid-roast, as adding more heat later risks a sudden spike in RoR that disrupts profile consistency. Excessively prolonged early drying can also contribute to baked flavours — particularly if the temperature curve flattens at any point during the extended low-heat drying phase.

Charge Temperature in Profile Replication¶

One of the most common causes of batch-to-batch inconsistency in a roasting programme is inconsistent charge temperature. Even a 5 °C variation in charge temperature changes the turning point, alters the early RoR, and shifts first crack timing — making it difficult to replicate intended profiles exactly. Roasters using data logging software (Cropster, Artisan) typically record charge temperature as the first data point in every roast and track it as a key consistency metric.

In high-volume production roasting, charge temperature is often managed through automated drum pre-heating protocols that bring the drum to a set target temperature before charging, ensuring consistency across multiple batches per day.

Key Facts¶

Charge temperature is the drum temperature at which green beans are loaded into the roaster
Typical range: 180–230 °C for drum roasters, but highly roaster- and batch-size-specific
Determines initial rate of heat transfer, turning point depth and speed, and early RoR
Too high → scorching and tipping defects; too low → prolonged drying, potential baking
Batch size, bean density, green moisture content, and ambient conditions all affect optimal charge temperature
Inconsistent charge temperature is a leading cause of batch-to-batch profile variation
Recorded as the first data point in roast logging software for every batch

References¶

Changelog¶

Date	Change
2026-04-27	Note created

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