I have recently seen a couple of baristas doing room temperature preifusion in both drip coffee and espresso when coffees are too fresh.
This doesn’t make any sense to me whatsoever and my gut is that it affects the coffee negatively, but i just want to know whether anybody has an opinion and more information about it.
I did do an experiment last week in two v60, one with cold water preinfusion and the other with hot water.
The one with cold water turned out to be bland, with muted tones and with a very unpleasant old fat flavor. But this is far from definitive.
One specific question is, does cold water drive CO2 out of the grounds?
Thanks in advance
I really don’t see the point of this. I presume they wet the grounds before locking the group in?
Gases are generally more soluble in cold water than hot water. However, there are several reasons I don’t think pre-wetting with cold water will release much of the CO2 from the ground coffee (relative to hot water):
- pressure influences the solubility of carbon dioxide much more than temperature (higher pressure increases solubility).
- increasing the temperature of a gas causes it to expand. So, if there is CO2 in the pores of the ground coffee, heating it up will force much of it out of the pores (and into the water). That won’t happen unless the water is at a significantly higher temperature than the ground coffee.
- it’s possible there will be carbon dioxide adsorbed (that is, stuck to the surface of) the ground coffee. The amount of CO2 which can adsorb to a surface is affected by temperature. Higher temperatures = less capacity to adsorb the gas = CO2 released in hot water (but not cold).
That said, there could be other reasons for the influence on taste.
For starters, the solubility (and the rate of dissolution) of coffee solids is lower in cold water. So the cold water will not dissolve as much coffee as the equivalent amount of hot water. This basically means you’ve diluted the resulting shot.
Additionally, the average extraction temperature will be lower, because there will be a mixing of the cold “pre-infusion” water, with the hotter extraction water. Which means the average extraction rate will also be lower = lower yield and lower TDS.
Thanks for your input @DIYCoffeeGuy
I agree with the things you say.
I have a few theories as to what influences the flavor, but i have no way to prove them, yet:
Room temperature water would lower the ground coffee temperature, which makes the extraction happen at a slower rate, and also at a lower temperature which in turn results in less solubles being extracted if the contact time is kept the same.
The coffee grounds absorb room temperature water and swell (even if they dont extract) which generates more resistance to the water, thus slowing down the extraction or keeping water from going deeper into the grounds. The result would be coffee less extracted.
Room temperature water creates channels, in the puck, which leads to uneven extraction.
There was a picture in Scott Rao’s instagram a couple of weeks ago in which he made a preinfusion for 30 seconds and realised that in that amount of time, the water doesnt get to penetrate to the center of the puck.
If that’s the case with hot water, imagine with cold…
Im with you in that “why bother” but still, it is an interesting topic.