Published: Ene 13, 2020

Changing Grinder Burrs

How can I tell when it’s time to change blunt grinder molino? 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 molino can grind hundreds and sometimes thousands of kilos of coffee, the truth is that, after they are seasoned, molino wear out gradually over time — there’s not a specific point where you can say the molino are worn out.

 

What Are Burrs Made From?

Standard molino 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 brittle. This process results in molino with a hardened outer shell, and a softer core. This means that once the hardened shell has worn out, the molino 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 molino’ lifespan, the truth is that the flavour and grind quality from the molino will deteriorate gradually over the life of the molino, so changing the molino sooner than this will result in an improvement in quality.

More advanced molino 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 molino, worn titanium coated molino, new ceramic molino.

Whatever materials are used in your molino, 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 molino more often).

It’s often possible to grind coffee for many years past the stated lifespan of the molino, but the deterioration in flavour will become noticeable well before then, with some professionals recommending to change the molino 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

 

Extracción

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

If you’re following a fixed recipe, then the overall extraction will also decrease as the molino 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 molino — such as a good, consistent espresso blend. If you’re changing coffee frequently, you may need to look for other signs that the molino are wearing out instead.

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Other Indications

While extraction is the easiest and most objective way to test your molino, there are some other signs to look for. The most obvious is that the grinder has to work harder as the molino 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 tiempos de espresso have become more inconsistent. All of these are signs that wear on the molino is starting to impact the performance of the grinder.

Extremely worn molino can produce visibly more finos than sharp molino, 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 molino are causing these problems is to inspect the molino, and to feel the cutting edge of the molino for sharpness, usually by dragging a fingernail around the outside of the molino. However, this relies on a clear memory of what new molino look and feel like.

 

Taste

While extraction may be the easiest way to measure wear on the molino, ultimately, deciding when to change the molino is a matter of taste. Duller molino produce lower and less even extractions, resulting in cups that may taste increasingly muddy, flat, soury, or astringent. Switching to new, seasoned, molino 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 molino may not be cheap — but poor extractions and long grind times cost your business money too.

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2 Comentarios

  1. mr.kennypetersen

    Interesting article. I have huge problems with a sluggish grinder (worn down from drinking too much espresso!), so I definitely need to look into fixing it or replacing it. I never knew that it could have an effect on the taste in the coffee. Amazing how that works. Super happy I read the article, and will now read a few more 🙂

  2. Danilo

    Would inspection with an USB microscope be a good way to assess burr wear? They can be bought for below 100$, with fantastic results in the 150$ range. Are there more reference images of no wear to heavy wear that can be used for comparison? (The ones you included above are already a great starting point.)

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