Zero Head Room
When it comes to storing your brewed coffee after it has finished brewing, there is only one good solution. At this point in the evolution of coffee technology, the best means of storage is to use vacuum flasks. Even this will maintain optimum coffee quality for only around half an hour after brewing.
Preheating
As we discussed in Lesson 1.01 of this course, the specific heat of a flask will determine how much heat is lost from the brewed coffee. Many flask designs have thick glass linings. This is beneficial for cleaning, but these linings have potential to reduce brew water temperatures by several degrees if they are not preheated.
Containing Volatile Aromatics
The loss of aromatic gases is difficult to prevent because aroma loss occurs even during the grinding and brewing process. To limit the amount of aromatics that are lost after brewing, the key is to seal up the coffee immediately. Systems that direct all the brewed coffee directly into a flask are the best at capturing aroma. However, it is essential to have the appropriately sized flask. Ideally, there will be no head room at the top of the brewer after the brew finishes drawing down. The flask should be brim full and hermetically sealed (i.e., sealed so that no air can leave or enter it).
The chemistry behind this approach is explained by the nature of volatility. A substance is volatile if it has a low boiling point. At the air/water interface, volatile aromatic compounds will continuously come out of solution and escape into the air as gases. One way to prevent this from happening is to reduce the size of the interface where the solution meets the air. (This is why flasks are usually designed to store a narrow column of liquid.) It is also essential to have as small an amount of head room as possible. This is to more quickly achieve what’s called an equilibrium vapour pressure.
Equilibrium occurs when the amount of volatile compounds escaping into the air is the same as the amount of volatile compounds dissolving back into the liquid. As the headspace above the brew accumulates more and more volatile compounds, it reaches a point at which their concentration in the gas (vapour pressure) is so high that they dissolve back into the liquid at the same rate that they escape — thus, no further net loss of volatile aromatic compounds occurs. However, one problem we have in keeping our volatile compounds in a liquid is their … volatility. It takes relatively less kinetic energy to get them to evaporate, and it takes relatively more vapour pressure to get them to condense.
When it comes to storing your brewed coffee after it has finished brewing, there is only one good solution. At this point in the evolution of coffee technology, the best means of storage is to use vacuum flasks. Even this will maintain optimum coffee quality for only around half an hour after brewing.
Preheating
As we discussed in Lesson 1.01 of this course, the specific heat of a flask will determine how much heat is lost from the brewed coffee. Many flask designs have thick glass linings. This is beneficial for cleaning, but these linings have potential to reduce brew water temperatures by several degrees if they are not preheated.
Containing Volatile Aromatics
The loss of aromatic gases is difficult to prevent because aroma loss occurs even during the grinding and brewing process. To limit the amount of aromatics that are lost after brewing, the key is to seal up the coffee immediately. Systems that direct all the brewed coffee directly into a flask are the best at capturing aroma. However, it is essential to have the appropriately sized flask. Ideally, there will be no head room at the top of the brewer after the brew finishes drawing down. The flask should be brim full and hermetically sealed (i.e., sealed so that no air can leave or enter it).