How can I tell when it’s time to change blunt grinder التروس? If you’re looking at your grinder, asking yourself this question, then it’s probably time to change them. While grinder manufacturers may claim that their التروس can grind hundreds and sometimes thousands of kilos of coffee, the truth is that, after they are seasoned, التروس wear out gradually over time — there’s not a specific point where you can say the التروس are worn out.

What Are التروس Made From?

Standard التروس are made from steel that has been ‘oil-quenched’ — a process that hardens the outer surface of the burr by rapidly cooling it. The rapid cooling induces the steel to form a specific crystalline structure called martensite that makes it harder and more هشًا. This process results in التروس with a hardened outer shell, and a softer core. This means that once the hardened shell has worn out, the التروس will wear much more quickly, as this post from the SCA’s Coffee Technicians Guild explains.

While this implies that there is a hard limit to the التروس’ lifespan, the truth is that the flavour and grind quality from the التروس will deteriorate gradually over the life of the التروس, so changing the التروس sooner than this will result in an improvement in quality.

More advanced التروس may have a thicker hardened layer, or be made from a material that is hard the whole way through (Chromoly Steel, Tool Steel or even ceramic). They may also be covered with a harder material such as the gold-colored titanium nitride (TiN) or ‘Red Speed’ coatings, which greatly extend the lifespan of the burr.

Images from left to right: very worn tool steel التروس, worn titanium coated التروس, new ceramic التروس.

Whatever materials are used in your التروس, choosing when to change them is essentially a compromise between quality and the cost of replacing them. However, there are a few indicators you can use to help you decide when to make a change.

Manufacturer Recommendations

Manufacturers publish a recommended lifespan for each burr design, so this is a good place to start. However, the way they come up with these numbers will vary between manufacturers, and they may be tempted to exaggerate the lifespan (or perhaps to underestimate it in order to sell new التروس more often).

It’s often possible to grind coffee for many years past the stated lifespan of the التروس, but the deterioration in flavour will become noticeable well before then, with some professionals recommending to change the التروس after as little as half of their recommended lifespan.

The following is a list of some manufacturers recommendations, which can be found on the Espresso Parts website, but we recommend looking up the current recommendations directly from your manufacturer, as these do occasionally change.

• Anfim Caimano (75mm flat burr) – change at 1,300lbs throughput
• Bunn G Series – change at 40,000lbs throughput
• La Marzocco Swift (64mm ceramic flat burr) – change at 3,300lbs coffee throughput
• Mahlkonig K30 – change at 1600lbs coffee throughput
• Mahlkonig EK43 – change at 14,300lbs coffee throughput
• Mahlkonig Tanzania – change at 8,000-10,000lbs coffee throughput
• Mazzer Mini (58mm flat burr) – change at 660lbs coffee throughput
• Mazzer Mini E – (64mm flat burr) – change at 660lbs of coffee throughput
• Mazzer Super Jolly (64mm flat burr) – change at 880lbs coffee throughput
• Mazzer Major (83mm flat burr) – change at 1,300lbs coffee throughput
• Mazzer Kony (63mm conical burr) – change at 1,640lbs coffee throughput
• Mazzer Robur 110V (71mm conical burr) – change at 1,700lbs coffee throughput
• Mazzer Robur 220V Three Phase (83mm conical burr) – change at 1,800lbs coffee throughput
• Nouva Simonelli MDX (64mm flat burr) – change at 1,200lbs coffee throughput
• Nouva Simonelli Mythos (75mm flat titanium burr) – change at 1,500lbs coffee throughput

الاستخلاص

A more objective gauge of when to change the التروس comes from measuring extraction. As التروس age, the evenness of extraction gradually decreases. This means that the highest extraction you can reach before اللاذع sets in (the extraction ceiling) will gradually decrease.

If you’re following a fixed recipe, then the overall extraction will also decrease as the التروس wear out (Rao, 2016, Socratic Coffee 2015). Extraction measurements however do rely on using the same or similar-enough coffee over the lifespan of the التروس — such as a good, consistent espresso blend. If you’re changing coffee frequently, you may need to look for other signs that the التروس are wearing out instead.

Other Indications

While extraction is the easiest and most objective way to test your التروس, there are some other signs to look for. The most obvious is that the grinder has to work harder as the التروس become less sharp, which means it makes more noise, generates more heat, and takes longer to grind the same amount of coffee.

You may also notice that the grinder produces more clumps (Socratic Coffee, 2015), or that the وقت تحضير الجرعات have become more inconsistent. All of these are signs that wear on the التروس is starting to impact the performance of the grinder.

Extremely worn التروس can produce visibly more الطحن الناعم than sharp التروس, resulting in muddy-looking beds in your brews, or more solids at the bottom of your espresso. However, by the time this happens, the other signs of wear have usually become fairly obvious.

The traditional way to determine if worn التروس are causing these problems is to inspect the التروس, and to feel the cutting edge of the التروس for sharpness, usually by سحب a fingernail around the outside of the التروس. However, this relies on a clear memory of what new التروس look and feel like.

Taste

While extraction may be the easiest way to measure wear on the التروس, ultimately, deciding when to change the التروس is a matter of taste. Duller التروس produce lower and less even extractions, resulting in cups that may taste increasingly muddy, flat, soury, or astringent. Switching to new, seasoned, التروس will give you bright, sparkling, and transparent flavours once more.

Because this deterioration in quality is a gradual process, you’ll need to make a decision on when it becomes too much for the level of quality you’re trying to achieve. But if you’re in any doubt, then it’s probably time to consider a change. Replacement التروس may not be cheap — but poor extractions and long grind times cost your business money too.