Why can't you get good coffee by putting half the normal amount of water and grounds in a moka pot? What goes wrong and why?

Or does it work?

I'm just curious.

By putting less water extraction will start on considerably lower temperature due to physical laws (more air above the water expanding). You can partially compensate that by using water that isn't cold (some trial-error needed to determine the right temperature)

But coffee from moka pot isn't especially good no matter what ...

Have you tried it?

A simple pencil and paper calculation suggests the initial extraction temperature will not be that much lower. And given how often people disparage moka pot coffee for its sometimes "burnt" flavor a lower temperature profile might be a good thing.

At least one moka pot on the market has an insert for the basket, to allow for using half as much grounds.

Yeah, I made a kind of spreadsheet in excel with some input parameters (like quantity of water, starting and ending pressure etc), giving me starting and ending temperature of extraction, that roughly matched the measurements. It was a nice opportunity to renew my knowledge from the school and university I forgot in the meantime. However, I wasn't satisfied with the coffee ... until later, when I made a kind of experimental pump espresso device out of it, which gives quite nice espresso for the fraction of the price of a lever machine

I can't tell from your post if you've ever brewed a half full pot or just ran a simulation in excel.

BTW burnt flavor in a moka pot is usually due to not stopping the extraction before it overheats. People dip the bottom in water to stop the extraction.

Gary, I know of that strategy. I usually just pour it quickly instead.

I have never brewed a half pot but I have overfilled the water reservoir. The overfilled temperature profile (blue line in graph) looked very much like the normally filled one except that it kept getting hotter as additional coffee was brewed.

So rather than interrupt the brew at the end, would it work to simply put less water in the reservoir to begin with?

I wouldn't know. I keep it simple and brew as designed, filling to just below the pressure relief valve and stopping the brew by dipping the bottom in water just as it starts to sputter. You could try a half full pot and see if it works (at your own risk, since it's to be used as designed). If not, smaller capacity ones are inexpensive enough online, especially ones that are used.

jpender wrote:I can't tell from your post if you've ever brewed a half full pot or just ran a simulation in excel.

Didn't actually try half, but was varying quantities of water, measuring the temperature (removed safety valve, fitted tyre valve and pushed a thermometer through it with piece of rubber as sealant) and comparing the measurements with calculation

There was a video that a guy made experimenting with Bialetti brika - a special model with overpressure valve, where he measured that temperature without valve was too low, unless warm water used. He didn't know that in brika, safety valve (which is a measure for quantity of water) is lower than in usual moka pot of the same size (from my remembering, 2 cup brika is the same size as 3 cup moka, but you put less water into it). I think it's in this thread, which should answer the question if you don't believe that my calculation (based on partial pressures of air and vapor and volumes) was correct

The secrets of the moka pot - How to video

Math behind that was explained in pdf mentioned in that thread too

Gary, I'm not too concerned about using "as designed". It's not going to explode if I fill it with less water.

For that matter, Bialetti's instructions don't included immersing the bottom of the pot in cold water at the end of the brew. So technically you're using yours out of spec as well. :-)