I must get 40 emails a day of people, absolutely livid, saying “what the f*ck is mosto and why is it in my coffee?” So I don’t have to keep emailing everyone, here’s a quick breakdown.
As coffee processing has evolved over the past decade in the wake of Sasa Sestic’s Barista Championship spotlighting carbonic maceration, many producers have sought to push the metaphorical envelope. More and more coffees are being described as “process forward” or other ambiguities– which is no slight, it’s just becoming more and more obvious over time that catchall terms are becoming less relevant at the fringes of coffee processing, as there become far more relevant details beyond ‘washed’ or ‘natural’.
One such borrowed innovation seeing more and more daylight in coffee processing is mosto. It is not a type of processing, rather a key element in a lot of advanced processing. I’ll try to be as concise as possible breaking this down.
Mosto (or must, which I have to say– I just do not like. I will not refer to any part of the coffee making process as including ‘must’, it’s not appetizing), is a term borrowed largely from winemaking. This is the product of the initial process of crushing grapes to produce juice, altogether with seeds, skins, stems and all. From there the solids and liquids are separated, and the extracted juice goes on its journey to become wine.
In coffee, mosto is generated as a byproduct of coffee fermentation. Clean, ripe coffee cherries are fermented, and as the cherry breaks down it releases juice. This thick, sugary juice is loaded with positive yeasts and bacteria that are helpful accelerants for fermentation (the same can be true of harmful bacteria, which is why it is important to carry out microbial tests to ensure safety and quality). This juice is separated from the solids of the fermentation, and the coffee finishes its processing and the mosto is kept to be used in future processing. (You may also see the term leachate used interchangeably, which is also technically correct, but it seems most folks universally agree that leachate feels like an intimidating or offputting word for what’s going on, and usually stick to ‘mosto’).
