You join a 60 m motor yacht and the crew mess machine is a two-group La Marzocco you have never touched. The second stew shows you the buttons and nothing else. Before you pull a shot for a guest, you need to know what each part of this machine does, because when something goes wrong mid-service you will have to diagnose it in thirty seconds.
Anatomy of the Espresso Machine
- Boiler: heats water. A heat exchanger machine has one boiler serving both steam and brew; a dual boiler has separate brew and steam boilers, giving independent, more stable brew temperature. Dual boiler is the better tool for a busy breakfast service.
- Pump: drives water through the coffee, conventionally at around 9 bar at the group. A rotary pump (plumbed in) is quieter and more stable than a vibratory pump.
- Group head: where the portafilter locks in. Contains the shower screen (distributes water over the puck) and the gasket (seals the portafilter). A perished gasket causes leaks and squirting.
- Portafilter: the handle. Holds the basket, which is sized for a dose (commonly 18 g doubles). Single, double and ridgeless/bottomless (naked) variants exist.
- Steam wand: delivers dry steam for milk texturing. Must be purged before and wiped and purged after every use.
- Hot water tap: for americanos and tea. Note that boiler water is not always ideal for tea.
- Drip tray and drain: on a yacht, know where the drain goes and whether it is plumbed or a manual tray you must empty.
The Grinder Is Half the Machine
A great machine with a poor grinder makes poor coffee. The reverse is far less true.
| Burr grinder | Blade grinder | |
|---|---|---|
| Action | Crushes between two burrs at a set gap | Chops randomly |
| Particle size | Consistent, adjustable | Wildly uneven |
| Espresso capable | Yes | No |
- Flat vs conical burrs: both work; flat burrs tend to a tighter particle distribution, conical burrs are common, forgiving and cheaper. Either is fine if properly adjusted.
- Stepless adjustment lets you make micro-changes to grind size, which is what dialling in requires. Stepped grinders can be too coarse in their increments for espresso.
- Grind size is the master control. Espresso needs a fine grind, roughly the texture of table salt to fine sand; filter is like coarse sand; French press is like coarse breadcrumbs.
- Dosing: grind on demand into the portafilter. Avoid old-style dosers that hold ground coffee. Weigh the dose on scales; do not trust a timer alone, because beans change with age and humidity.
Burr Wear and Retention
- Burrs are consumables. Domestic burrs may last 200-400 kg; commercial steel burrs far more. Worn burrs produce fines and inconsistent shots that no dialling in will fix.
- Retention is ground coffee left inside the grinder. Stale retained grounds contaminate the next shot. Purge a few grams after a grind size change or after a long idle period.
Onboard Notes
- Espresso machines are heavy, hot and full of pressurised water. They must be physically secured in a seaway. Know how yours is mounted and never operate a poorly secured machine under way.
- Machines draw serious current. Confirm with the engineer before plugging anything new into a galley circuit.
- If shots suddenly change with no other cause, check for a loose grinder collar, worn burrs, or a portafilter not seating cleanly on the gasket.