Fresh is best
On a recent visit to a coffee shop a sign was spotted which read, "freshly ground coffee sold here". An espresso was ordered and the anticipation of getting a great drink began! However, the familiar sound of a coffee grinder couldn't be heard so how fresh was this freshly ground coffee really going to be? And would the fact that pre-ground coffee was being used make any difference to the drink?
Sadly, the coffee didn't taste great and there are many reasons why this might be the case. The fact that the coffee was pre-ground was a significant contributor. So, how quickly should coffee be used after it has been ground? Clearly sooner than in the example described above! But at what point is the taste of the coffee affected by the fact that the beans have been pre-ground?
Let's think about the journey the coffee bean takes before it can be used to make a drink. The green bean is very unpalatable before roasting. The application of heat during the roasting process is an essential catalyst in creating the desirable flavours we expect in our coffee. The length of time the coffee is roasted and the temperature used can have a massive impact on the flavour. In addition a large amount of gas builds up in the bean during the roasting process and it is this gas that contains the wonderful coffee aroma.
So much of what we taste is linked with what we smell, therefore it makes sense to keep the gas in the coffee bean for as long as possible. The roasted beans are fairly stable but some gas will escape after the coffee has been roasted. This is why you get that amazing smell when you open up a bag of coffee! The longer the coffee is left after roasting the more gas will escape. With that in mind, all our coffee is roasted on the day of ordering to ensure you get the freshest possible beans and we recommend you use it within six weeks of roasting to get the best flavour.
Grinding the coffee breaks up the structure of the bean and significantly increases its surface area. As a result much of the gas escapes. This results in a rapid degradation of the coffee which has a huge impact on the taste. We begin to taste undesirable flavours in the coffee such as bitterness. In as little as 15 minutes you can taste the difference between fresh and pre-ground coffee. You will also see the difference in the way the coffee extracts. Instead of a beautiful, rich looking crema on top of your espresso it will have a much blonder watery appearance.
So then, there are a couple options open to a coffee shop owner when it comes to their ground coffee supply: buy pre-ground coffee or grind it on site. Thankfully the majority chose option two! Most commercial machines are burr grinders, these are very efficient at crushing the coffee beans to a uniform size. The size of coffee grounds can be changed to make the coffee coarser or finer by moving the burrs further away or closer together. The speed the hot water travels through the coffee grounds can make a big difference to the taste of the espresso. If the coffee is purchased pre-ground there is no opportunity to change the size of the particles.
The next question is what type of burr grinder to purchase; we supply on-demand and doser grinders. An on-demand grinder grinds the coffee for each shot. It works on a timer system; we set the timer to give us the desired dose for each espresso. Whereas, with a doser grinder we grind the coffee into a chamber and then dose the coffee out using a lever. However, we need to resist the temptation to fill the doser chamber with pre-ground coffee because the ground coffee will quickly begin to degrade.
Ideally then, whichever grinder you use, apply the principle of only grinding what you need for each espresso to ensure you are providing the freshest cup possible for your customers.