Make machine behavior visible
Temperatures, rate of rise, and the machine's own readings together, while the roast is happening.
RoastRacc
A project from Racc Roasters · El Salvador
A roasting app built to speak up, not stay quiet.
RoastRacc is a free, browser-based roast monitor, logger and profile player for the Mill City MCR-2D. It watches the roast with you, says out loud what it notices, and leaves the decisions, and the controls, with the person at the roaster.
Free and open source (GPLv3) · Runs in Chrome or Edge · Used on every roast day at our roastery. An independent project, not endorsed by or affiliated with Mill City Roasters.
The idea behind it
Built for the person doing the roasting, not just watching a screen.
A small roastery is a working environment. The person roasting may also be weighing batches, moving green coffee, packing bags, or getting the next order ready. Software that assumes someone can stare at a screen every second isn't designed for that reality.
So RoastRacc talks. It tells you what's loaded, when the roast drifts, when to think about a change, and when to drop. Whatever it says also stays on screen and in the roast's record, because a roastery is loud.
It is a practical tool built by a roaster for a real production environment, not an attempt to turn every roastery into a laboratory.
What matters
Six priorities. In that order.
Make problems harder to miss
Explicit alarms, stale-reading warnings, and a voice that says what changed, so nothing depends on someone happening to look.
Keep the operator in control
Profile playback can guide a roast, but the person at the roaster can take over at any moment, and RoastRacc gets out of the way.
Keep the record
Every roast saved with its curve, weights, color and what was said, stored locally and exportable rather than locked behind an account.
Fit a small production roastery
Useful on a busy roast day, without an enterprise workflow or a dedicated person watching a dashboard.
Keep the setup understandable
One browser page, clear settings, and portable profile files, so you can work with it on your own terms.
Inside RoastRacc
A roast day, start to finish.
RoastRacc follows the way a roast day actually runs: getting ready, the roast itself, the drop, and the record afterwards.
01
Before the roast
- Plan the dayLine up the day's batches on the Plan tab, or import them from a simple plan file (an example is in the download), and see how much green each lot needs.
- Your coffeesAdd, retire and code your coffees inside the app. One coffee can run another's profile without copying it.
- PreheatWarm-up monitoring helps you know when the machine is ready to charge.
- Check by earWhen a profile loads, RoastRacc says the coffee and batch size out loud.
02
During the roast
- Live readingsBean, exhaust, drum and inlet temperatures with rate of rise and the machine's settings, next to a ghost of the reference roast.
- Profile playbackReplay a profile's gas, fan and drum steps, with manual override always available.
- Pace alertSays when the roast runs ahead or behind its reference, gives an early heads-up, and can suggest a small trim or taking manual control.
- Alarms you can't missMachine conditions, stale readings and lost communication are announced, and control goes back to you.
03
At the drop
- DoseMatchMoves the drop to follow the heat the beans have actually had, so a batch running hot or cool lands closer to its reference.
- Visible countdownThe DROP button counts down, and the chart shows the DoseMatch drop next to the plan's.
- Never goes quietThe drop is still called after you take manual control.
- Your choiceSwitch DoseMatch off for a plain countdown from the profile.
04
After the roast
- Cool downStatus stays on screen with drum temperature and time remaining.
- HistoryEach roast keeps its curve, roasted weight, weight loss and, if you use a color meter, bean and ground color.
- Records that catch mistakesUnconfirmed weights and unrecognized coffee names are flagged for review.
- Exports and backupCSV exports and a one-click backup of everything.
Pace alert & DoseMatch
It notices when the roast drifts, and helps you decide when to drop.
No two roast days are quite the same. Room, weather, airflow and the machine itself all move a little, and a profile replayed perfectly can still run hot or cool. These tools watch for that and say so out loud.
The pace alert compares the bean temperature with the reference profile once the roast has settled. When the roast runs noticeably ahead or behind, and stays that way long enough not to be noise, RoastRacc says so plainly. Where you would normally adjust, it can suggest a small trim; if the drift is bigger than a trim should fix, it suggests taking manual control and names a setting to aim for.
DoseMatch looks at the end of the roast. Instead of counting down to the profile's drop on the clock alone, it tracks how much heat the beans have actually had, giving hotter moments more weight, and moves the drop so this batch lands where the reference did. A roast running hot hears "drop" a little earlier; one running cool, a little later. Read the idea behind it on our blog.
On our own roast days, DoseMatch's drop cues have landed close to where we'd drop by hand, and batches of the same coffee dropped at its cue have come out with very similar weight loss and roast color. We haven't shown that it makes better coffee in the cup.
Made at the roastery
Shaped by real roast days.
RoastRacc was built at Racc Roasters to solve practical problems in a working roastery, and it is shared in case other roasters find it useful too. It isn't trying to be everything to everyone.
Used every roast day
It runs our own roaster. Most changes start as something we noticed during a roast: a cue we wanted to hear, a mistake we wanted caught sooner.
Reviewed before release
Each version is tested against real roasts from our own roast days, and the changes get an independent code review before they go out.
Written down
Every download includes the manual, with a technical reference section, and a version-by-version changelog of what changed and why.
v1.40Latest release · October 2026
Roast color in the record. If you use a color meter, bean and ground readings now sit next to weight loss in History and go out with the CSV export.
Engaging mid-roast keeps your hand settings. Pick the profile back up partway through and it carries on from its next step instead of undoing your trims.
Plus smaller fixes from the last roast day. The full list is in the changelog inside the download.
Before you download
The technical essentials.
The few things you need to know before trying RoastRacc on your setup.
Browser and connection
Chrome or Edge only. RoastRacc uses browser serial-port support, which is not available in Firefox or Safari.
Live use requires USB. Connect to the roaster's PLC over USB. No roaster yet? Demo mode runs without a machine connection.
Hardware compatibility
RoastRacc was built and tested on one machine: a Mill City MCR-2D with a Delta PLC.
Other machines and configurations are unverified. Before relying on the readings, compare them against the physical control panel and confirm that your setup behaves as expected.
Control and automation
- Manual control is the default. Automation is opt-in; gas, fan, and drum are not controlled by a profile unless you engage it.
- The panel temperature setpoint is read, never written. RoastRacc does not write to that setpoint.
- Manual control takes priority. Disconnecting USB returns you to the roaster's manual controls immediately.
- Uncertainty should be visible. If RoastRacc cannot confirm a write, a reading, or the USB connection, it reports the problem and hands control back rather than continuing silently.
Important: Verify an untested machine configuration before using RoastRacc in production. Software monitoring and alarms are not a substitute for the roaster's own safety systems, operating procedures, or operator judgment.
Your records
Your roast data stays yours.
Roast records are how a roastery learns and reproduces its results. RoastRacc keeps them in the browser on the computer running it. There is no account, email address, or subscription, and nothing is uploaded anywhere.
That also means backups are your job. Use the one-click backup or the CSV exports, and point your browser's downloads at a folder your own system backs up. Profiles move easily between computers; roast history stays in the browser it was recorded in until you export it.
Clearing browser data can remove local records. Check that your backups work before you rely on them.
RoastRacc v1.40 · Built in El Salvador
Take a look. See if it fits your roastery.
Download the testing package, review the setup requirements, and read the manual before connecting RoastRacc to a machine.