Batch Size Scaling

Batch size changes how a Roest behaves mechanically, thermally, and diagnostically. The same profile can produce different sensor curves, crack behavior, pressure, roast time, weight loss, and cup profile when moved from 50g to 100g, 150g, 180g, or 200g. This page explains how to choose a batch size, how to scale profiles, and what secondary settings usually need to change with dose.

Core Rule: Batch Size Is Not a Linear Multiplier

Changing batch weight is not just “more coffee needs more heat.” It changes the air-to-bean ratio, how much of the drum is occupied, how well probes contact beans, how much hot air escapes to the exhaust, how much momentum the bean pile carries, and how aggressively the paddles move the coffee. Several contributors describe 50–100g as behaving more like a small air/fluid-bed roast, while 180–200g behaves closer to a fuller drum-style roast with more retained heat and more internal development 2 sources.

For that reason, profiles should not be transferred blindly across batch sizes. A 50–100g profile will not work unchanged on 180–200g, and a 180–185g profile can be too fast or too airflow-heavy when charged at 150g 2 sources. Batch changes should be treated as profile changes involving inlet temperature, power curve, airflow/pressure, and drum speed.

Practical Starting Points by Batch Size

Use this table as the canonical starting point for selecting a batch size. These are not universal recipes; they are community-supported working ranges and should be adapted to the machine, coffee, voltage, altitude, and airflow setup.

Batch size	Best use	Starting assumptions	Main cautions
50g	Cupping, offer samples, green evaluation, tiny sample quantities	Use inlet/time or ET/inlet-style profiles; expect weak or unreliable BT/RoR data. Some users run 50g sample roasts around 4–6:45 depending on profile and workflow 2 sources.	Not ideal for brewing/filter evaluation; first crack may be sparse and BT may show high crack temperatures around 225–230°C 2 sources.
80–100g	Small samples, repeated experiments, limited greens	Useful when sample size dictates it; 100g is common for sample workflows. RoR and BT should be interpreted cautiously, especially around first crack 2 sources.	Graphs may look bad even when the roast cups well; washed coffees can show BT flattening or negative RoR near crack. Use Bean Temperature Profiling conservatively.
120–130g / 125g	Better sample size when enough green is available	A common compromise: better BT contact than 100g, still economical, and practical for splitting 250g or 1kg samples. Roest has been quoted as recommending 125g as an ideal/best weight ratio; one contributor notes 125g gives good BT coverage without impacting the ET probe and good agitation 2 sources.	Still not identical to 150g+ behavior. Some users like 120–130g, but others report little improvement over 100g depending on coffee and profile.
145–150g	General learning, home roasting, stable logs, moderate output	Often recommended for starting out and for more reliable graphs than 100g. Several users treat 150g as a practical sweet spot; 55 rpm is commonly cited as workable at 150g 2 sources.	Cooling may become a limitation on stock cooling, and some machines/profiles need airflow or inlet changes versus 100g.
160–185g	Drinking/brewing roasts, more traditional cup structure, stronger BT data	A strong default for consumption roasts when green quantity and cooling allow it. Community reports often describe better heat retention, more body/sweetness, and more realistic BT behavior than 50–100g 2 sources.	Requires stricter cooling and maintenance. Beans can enter the chute or exhaust depending on bean size, expansion, airflow, and RPM.
200g	Advanced/high-output experiments, some production workflows, Ultra/counterflow users	Possible and sometimes preferred for stability, complexity, and development, especially by users deliberately working around its limits 2 sources. Use lower drum speed: Roest guidance is repeatedly quoted around 40–45 rpm for 200g 2 sources.	Not universally viable. Risks include beans in chute/exhaust, drum stalls, loss of ET usefulness, and cooling limitations. Do not assume 200g works on every model, coffee, or workflow.
220–250g+	Experimental only	Some users report tests at 220–250g, especially with counterflow/tilt or small beans, but this is outside the conservative working zone 2 sources.	Needs fast cooling and careful safety checks. 250g can be messy or bean-size dependent, and 300g has been reported to jam from the start source.

How to Scale a Profile

A profile should be rebuilt around the new batch size rather than linearly scaled. The most robust approach is to keep one variable fixed long enough to understand the new batch behavior, then adjust in a controlled order.

Choose the target batch size and stay there while dialing in. Changing even 5–10g can materially change timing and sensor behavior on some profiles source.
Match the profile type to the batch size. Use inlet/time or power/time for 50–100g when BT is noisy; BT/inlet profiles require enough coffee mass for more reliable BT feedback, with 120g+ commonly cited as the point where readings improve 2 sources.
Adjust heat application by batch size rather than applying a single percentage multiplier. Roest forum guidance quoted in the community suggests increasing a 100g profile by 5–10% power for 150g, but other experienced users warn that batch-size dynamics change the whole power/heat approach rather than simply scaling up or down 2 sources.
Re-check airflow and pressure for the new batch size. Fan percentages are not portable between machines; identical drum pressure may require very different exhaust percentages, even for the same nominal batch size 2 sources.
Re-select drum speed. For 100–120g, Roest guidance quoted by users recommends at least 55 rpm for energy efficiency; for 200g, guidance repeatedly drops toward 40–45 rpm to reduce beans getting stuck or entering ventilation exits 2 sources.
Confirm by taste, color, and weight loss rather than graph beauty alone. At 50–100g, good roasts may have unattractive BT/RoR curves because the probe is not consistently embedded in the bean pile 2 sources.

A useful working heuristic from community testing is that smaller batches need a gentler start and less dramatic late heat reduction, while fuller batches need more early energy but allow more reduction after drying because momentum carries forward 2 sources. For profile shape, one contributor describes peak power moving later for 50–100g, toward center/right for 130–150g, and earlier/left for 190–200g source.

What Changes When Batch Size Changes

Sensor behavior

Batch size strongly affects BT, ET, exhaust, and RoR interpretation. At lower weights, the bean probe may read a mixture of hot air and bean-surface temperature because the bean pile does not consistently cover the probe. This makes RoR especially noisy because RoR is derived from BT 2 sources.

At larger weights, BT often becomes more useful, but ET and exhaust can become less representative if beans expand into the probe area or alter airflow. Roest has been reported as saying that at 150g the air temp and exhaust sensors are no longer reliable; others report ET becoming useless around 180–200g or when beans touch the ET area 2 sources.

Yellowing temperature markers also shift with batch size. One commonly cited approximation is ~170–175°C BT for 100g, ~160–165°C for 150–165g, and ~150–155°C for 180–200g, while acknowledging that visual yellowing is subjective source.

Heat retention and exhaust behavior

With fewer beans, more hot air can pass through the chamber and out the exhaust; with more beans, the bean pile can restrict or “plug” the airflow path and retain more heat. This is why lower-dose roasts can show higher ET/exhaust temperatures even when less heat is reaching the bean mass 2 sources.

A fuller batch can also make the internal temperature environment more even by reducing empty air space. This is one reason some users report more body, sweetness, inner development, and less hollow/tea-like cup character when moving from 100g toward 150–200g 2 sources.

First crack detection

First crack sound and automatic detection are batch-size dependent. Small batches can amplify crack sound because the chamber is emptier, while 170–200g can dampen sound because the bean mass absorbs or blocks it 2 sources. At 50g, users may hear only a few scattered cracks; at larger batches, the machine may undercount cracks even when beans are audibly popping.

Because of this, several experienced users prefer manual marking, temperature-based dropping, or sensory/color/weight-loss validation over trusting crack count alone. See First Crack Management and Development Time and Drop Decisions.

Weight loss and color

Lower batch weights often show higher weight loss than larger batches under comparable roast goals. One user states that 100g roasts generally lose more than 180g roasts, and another reports lower weight loss at 190g than 100g 2 sources. Weight loss remains bean- and profile-dependent, so it should be interpreted alongside color, aroma, and cup results; see Weight Loss Targets.

Color comparison across batch sizes can be misleading. Roasts with the same or similar measured color can taste quite different, and 100g versus 150–190g batches may differ in body, sweetness, acidity, and aftertaste even when visual color appears close 2 sources. Use a consistent grind and meter workflow if comparing color; see Color Reading and Measurement.

Small Batches: 50g to 100g

Small batches are valuable for samples, experiments, and situations where green coffee is scarce. They are not simply “mini versions” of 150–200g roasts. Users repeatedly warn that 50–100g data can be janky, especially BT and RoR, and that cup results should be judged by cupping, brewing, aroma, color, and weight loss rather than graph appearance.

50g is widely framed as a cupping/sample size, not a brew-production size. Christopher Feran states that 50g is good for cupping only, and denis6004 says fast 50–100g sample roasts are for cupping/evaluation, not brewing/drip 2 sources. That said, several users have achieved useful 50g profiles, especially with inlet/time or carefully downscaled profiles.

100g remains common because many samples arrive in 100g quantities, but it is sensitive. At 100g, changes in airflow, inlet, RPM, and probe contact can produce large graph artifacts. For 100g workflows, some users ignore RoR, use longer smoothing intervals, or rely on inlet/time rather than BT/inlet feedback 2 sources.

Mid-Size Batches: 120g to 150g

The 120–150g range is the compromise zone. It gives better BT coverage than 50–100g while avoiding some of the mechanical and cooling complications of 180–200g. 125g is repeatedly cited as a useful or “ideal” size because it improves BT coverage, avoids impacting the ET probe, and works well for splitting samples 2 sources.

150g is frequently recommended for starting out because the graph data and roast behavior make more sense than at 100g, while remaining easier to manage than 200g. Patrickj2095 says 150g is nice for starting out, and other users report 120–150g as the range where graphs make the most sense source. If a 100g profile is being adapted to 150g, the community has quoted Roest forum guidance to add 5–10% power as a starting experiment, but this should be treated as a starting point rather than a universal scaling law source.

Larger Batches: 160g to 185g

The 160–185g range is often favored for drinking/brewing roasts. Users report better heat retention, more realistic BT data, more body and sweetness, and more traditional roast behavior than 50–100g. Denis6004 repeatedly describes 170–185g as his preferred range for personal drinking because it gives more consistent results and more inner development with less development time source.

For S100/L100-style machines, 180g ±5g is described by one experienced user as a sweet spot, while 180–185g is also described as a safe bet depending on bean size 2 sources. Another practical batch-planning compromise is 166.5g, which divides 500g and 1kg green quantities evenly and has been used as an adaptation of 185g profiles 2 sources.

Cooling and maintenance become more important above 150g. Stock cooling is described as acceptable for 50–100g, but too slow for 150–200g by one user; another user reports effective vacuum cooling of 170–185g batches in 30–45 seconds 2 sources. curated If using vacuum or external cooling, keep hot beans and chaff out of household vacuum motors and plastic dust containers unless the setup is specifically heat-safe and uses an appropriate separator or metal collection path. See Cooling and Between-Batch Protocol.

200g and Above

200g is possible, but it is not a neutral upgrade. It changes drum fill, airflow, RPM constraints, sensor usefulness, cooling, and risk of beans entering the chute or exhaust. Some users report excellent 200g results, more stability, clearer cracks, and deeper development; others call 200g suboptimal or too risky for their machine and workflow 2 sources.

For 200g, the dominant practical constraint is drum speed. Roest guidance is repeatedly quoted as recommending 40–45 rpm or below 40 rpm for 200g to keep beans from getting stuck or entering the exhaust/ventilation exit 2 sources. Some users report successful 200g batches at 35 rpm or 39 rpm, while others report beans in the chute or stalls depending on bean size and machine 2 sources.

200g also changes sensor interpretation. ET can become less useful because beans may cover or contact the sensor area, while BT can become very stable in some setups 2 sources. If using 200g, validate by taste, weight loss, color, and mechanical inspection rather than assuming the 100g or 150g graph logic applies.

Conflicts and Limits

CONFLICT (Unresolved): ideal batch size. Roest is quoted as recommending 125g as an ideal or best weight ratio, while some experienced users prefer 150g, 160g, 170–185g, or 200g depending on purpose. Christopher Feran describes the machine as best around 120–150g and 200g as suboptimal in his opinion; denis6004 often prefers 160–185g or 180g ±5g for drinking roasts; sorinl has reported preferring 200g for stability and complexity in some contexts 2 sources. The practical resolution is use-case based: 50g for cupping samples, 120–150g for reliable small-batch profiling, and 160–185g for many drinking/brewing workflows.

CONFLICT (Unresolved): 200g viability. Tom Roest and several users report 200g can work, especially with counterflow or correct RPM, while other experienced users warn that 200g causes beans in the chute, ET loss, stalls, and cooling problems on some setups 2 sources. Treat 200g as an advanced batch size rather than a default.

CONFLICT (Unresolved): scaling by percentage. Roest/forum guidance quoted by users suggests adding 5–10% power when scaling a 100g profile to 150g, but other trusted contributors argue that batch size changes the whole thermal and airflow system and cannot be treated as a linear up/downscale 2 sources. Use percentage changes only as a first test, then rebuild around sensory and log results.

Troubleshooting Batch-Size Problems

Symptom	Likely batch-size cause	Fix
BT/RoR crashes or looks nonsensical around first crack at 50–100g	Probe not consistently embedded in bean pile; RoR derived from noisy BT	Ignore graph beauty, use inlet/time or power/time, increase smoothing, or move to 120–150g for better BT feedback 2 sources.
Profile runs much faster after reducing batch size	Lower bean mass, more hot air bypass, different air-to-bean ratio	Reduce inlet/power, use gentler start, or rebuild the profile for the smaller batch.
150g charged into a 160–185g profile runs too fast or too negative at the end	Profile airflow/heat assumes more bean mass	Reduce final exhaust 5–10% or adjust inlet/BT points rather than copying the larger profile unchanged source.
Beans enter chute/exhaust at 180–200g	Too much volume, high airflow, high RPM, expansion, bean shape	Reduce batch by 5g at a time, reduce RPM, inspect chute/exhaust, and avoid 200g if recurring 2 sources. curated Treat beans or chaff in the chute/exhaust as a safety issue, not just a roast defect: let the roaster cool, inspect and clear the chute/exhaust path before the next batch, and do not continue using a setup that repeatedly sends beans into the exhaust.
Stock cooling leaves larger batches hot	Roasted mass exceeds stock cooling comfort zone	Use longer BBP/cooling time or a stronger external cooling solution; stock cooling is mainly described as comfortable for 50–100g source.
Same profile tastes thin or under at 100g but fuller at 150–190g	Lower batch mass and more convection/bypass at 100g	Use a 120–150g compromise or rebuild the 100g profile with different heat shape rather than chasing the 150g graph.
A profile shared by another user misses crack or runs too fast	Machine variation, voltage, altitude, exhaust path, pressure, or batch-size mismatch	Treat shared profiles as starting points only and adjust for the local unit; see Profile Sharing and Starting Points and Calibration and Environment.

Batch Planning and Green Quantity

Batch size also affects how green coffee is divided. 100g is convenient for 1kg lots and common sample bags, while 125g divides 1kg into 8 batches, 150g works well for 1lb blocks as 3 × 150g, and 166.5g divides 500g or 1kg evenly into 3 or 6 parts 2 sources. Some users prefer 165–185g but accept odd splits or blending leftovers to avoid very small remainder batches 2 sources.

When learning, it is better to buy enough of one green coffee to repeat and compare roasts rather than buying many tiny lots. One recommendation is to buy 5kg of the same green instead of 5 × 1kg so the roaster can learn from repeated trials on one coffee source.

Batch-size decisions interact strongly with Airflow and Fan Settings, Pressure Management, Drum Speed / RPM Settings, Inlet Temperature Management, Bean Temperature Profiling, Cooling and Between-Batch Protocol, and Roast Defects Troubleshooting.