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Grinder retention is the amount of ground coffee that stays inside the grinder after dosing — sitting in the chute, clinging to the burrs, or collecting in the doser chamber. It sounds minor but retention has a real effect on shot consistency, freshness, and your ability to dial in accurately. Understanding it helps you get more repeatable results and know what to look for when choosing a grinder.
Every grinder retains some ground coffee between uses — stuck to burrs and surfaces through static electricity, sitting in a chute waiting to fall, or held in a doser chamber. When you grind for your next shot, this old coffee is pushed out first, mixed into your fresh dose. If you ground yesterday, that retained coffee is a day old. If you changed your grind setting, the retained coffee is at the old setting. In both cases, your dose contains coffee that is not representative of what you just ground.
When you change your grind setting — as you do repeatedly when dialling in a new coffee — the effect of that change does not appear immediately. The first shot after a grind adjustment contains a mix of old and new grind. The more retention your grinder has, the more shots it takes before the new setting is fully expressed. High-retention grinders can require 3-5 shots to fully transition between grind settings, making the dial-in process slower and more expensive in coffee terms.
Traditional doser grinders (common in older home setups and cafes) grind into a chamber and dispense measured doses. These typically have very high retention — sometimes 5-10g or more of old coffee sitting in the system at any time. Doserless grinders grind directly into the portafilter and retain much less — typically 0.5-2g. Modern single-dose grinders are specifically designed for near-zero retention: they are built to deliver almost all ground coffee into the portafilter with minimal left behind.
The simplest way to deal with retention is to purge: grind 2-3g of coffee (which flushes out the old grounds from the previous session) before grinding your actual dose. Discard the purge grounds. This is particularly important on high-retention grinders, first thing in the morning, and any time you change grind settings. Some baristas weigh their ground dose after purging to ensure consistency regardless of what the grinder retained.
The trend toward single-dose grinders — grinders with no hopper, designed to grind one dose at a time — is partly a response to the retention problem. Without a full hopper, there is nothing to fall through the grind path between uses. Ross Droplet Technique (RDT) involves adding a tiny amount of water (a few drops) to the beans before grinding, which reduces static electricity and dramatically cuts how much coffee clings to the chute and burrs. A fine mist from a small sprayer or a few drops from a fingertip works well and does not affect extraction.
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