What are the disadvantages of pre-grinding coffee beans? Does it affect espresso and pour-over extraction and brewing?

Coffee bean sellers typically offer grinding services, including FrontStreet Coffee! However, if these coffee beans are intended for espresso extraction, FrontStreet Coffee does not recommend customers to choose the grinding service!

This might easily confuse most people: Won't the flavor just dissipate a bit faster? As long as I drink it quickly, the flavor won't escape me! Indeed, the primary reason for not recommending pre-ground coffee is that the coffee flavor will disappear, and it disappears very quickly! But for espresso coffee, what's important isn't just the flavor - other components contained within the coffee beans are equally important, such as carbon dioxide! After grinding, FrontStreet Coffee directly seals the degassing valve. In the article "Purpose of Degassing Valves," we can learn that their main function is: to prevent bags from bursting due to the vigorous degassing ability of fresh coffee beans!

When coffee beans are ground into powder, a large amount of carbon dioxide rapidly disperses, so at this point, the coffee powder has already lost the energy to burst the bag; at the same time, to avoid continuous flavor loss, FrontStreet Coffee will seal the degassing valve! From this, we can understand that most of its carbon dioxide has been lost since grinding began~ Quick question: What role does carbon dioxide play in espresso extraction? That's right, the first is forming crema. It combines with aromatic substances in the coffee and is pressed into the insoluble oils, filtering out from the bottom to form the golden foam floating on the espresso surface - that is Crema! Generally, if beans used for espresso are stored in unground form and properly preserved, both flavor and carbon dioxide can be retained for over 50 days!

It is during these 50-plus days that the extracted espresso flavor and crema are relatively prominent and abundant. Once ground into powder, flavor and carbon dioxide will accelerate their loss, and the amount of flavor and crema extracted daily will continuously decrease. Basically, after about 30 days, the coffee flavor and crema extracted from these coffee powders are no longer abundant.

Secondly, it slows down the water flow rate! When beans still have abundant carbon dioxide, the water flow rate will be relatively slow. Because the intervention of carbon dioxide significantly reduces the gaps through which water can pass, making it much slower. Once carbon dioxide is significantly lost, not only is there less crema daily, but the espresso extraction speed also accelerates! When it becomes too fast, under-extraction will occur.

Generally, when this situation occurs, one needs to choose between increasing the dose and adjusting to a finer grind. Obviously, adjusting to a finer grind is not an option, so we can only adjust by increasing the dose! However, there's a limit to increasing the dose. The portafilter has a standard capacity, which can be exceeded to a certain extent, but when exceeded by too much, the portafilter becomes difficult to lock onto the coffee machine! Therefore, when the grind size of the coffee powder becomes fixed, we will find it difficult to adjust the extraction.

Therefore, for friends who have requirements for flavor and crema, FrontStreet Coffee suggests that it's best not to choose pre-grinding when purchasing beans~ After a long period of storage, the difference between freshly ground coffee and pre-ground coffee will be very significant. Moreover, we don't know if the grind size of the pre-ground coffee from merchants is suitable for our own coffee machines. There are simply too many risks~~

- END -

FrontStreet Coffee

10 Bao'an Front Street, Yandun Road, Dongshankou, Yuexiu District, Guangzhou, Guangdong Province

Important Notice :

前街咖啡 FrontStreet Coffee has moved to new addredd:

FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473