Today's blog focuses on one of the unsung heroes of the roastery... the destoner...
Bags of coffee beans are filled with coffee... duh!... but sometimes unwanted travellers make their way into those bags. I'm talking about stones and sometimes metal objects (screws, nuts, bolts). These problem children can be very small... and difficult to detect. Stones and metals objects generally get picked up with natural process coffees where the beans are left to dry in the sun in order to macerate the cherry of the fruit so facilitate depulping and access to the seed.
When I first started to seriously commit to this business, I spoke to a number of my green bean suppliers and they all suggested that we'd be able to visually identify stones because of the relatively small scale of the operation. However, one part of my skill set is risk management (I spend a fair proportion of my week advising companies on their risk management processes) and I'm obsessed with mitigating low probability but high impact risks. Stones and metal objects fall into this category for roasted coffee... they're not seen frequently, but if they end up in your grinder they can cause damage (sometimes destroying burr sets).
Investing in a destoner was our mitigation process for this risk. The destoner works by taking advantage of the density difference between roasted coffee (less dense than green beans which are, in turn, less dense than dangerous stones and metal objects) and our unwanted travellers. A fan produces a fluid bed on which the roasted coffee rides, and the stones fall to the bottom of the screen allowing them to picked out at the end of the session. Here's an photo looking into the innards of the destoner at the end fo a batch.
The image at the top of the blog post shows you the stones we've identified this week. I'm glad they're not in position to have impacted any of your burrs!
To learn about filtering espresso click here
To read about new green bean arrivals click here