jpender wrote:What happens with espresso in high humidity?

I've made coffee in Hawaii with the windows open but it wasn't espresso. The only thing I noticed was that there was absolutely zero need for RDT.

I don't understand it really, but I know living in a 1929 year old home with no air conditioning for going on 30 years this Fall--doesn't matter what grinder, what espresso machine (and I've had a myriad of machines in 30 years)--high heat & humidity causes my espresso to run fast no matter how I try to compensate (more grams of beans, finer grind, even harder tamp).

I found this on Coffee Gems Artisian Roaster's blog, "Coffee is a very sensitive and delicate product so any variation in atmospheric conditions will impact its density. This is one of the reasons that you should empty the chamber of your grinder every night, and start with fresh coffee beans in the morning. On a humid day, or on a day that becomes humid, the coffee beans will absorb water from the air more quickly than on a dry day.

If you do an extraction with coffee that had been exposed to humidity, the water from the espresso machine will not penetrate it as quickly. This will produce a slower extraction than normal. Essentially, as a day grows humid, the effect on extraction is the same as if the grind got finer. Humidity will slow the extraction down. You have to compensate by making the grind a little coarser.

Equally, on warmer days (or changes from chilly to hot days as in Spring or Summer), the espresso will tend to extract slightly faster. The effect of dry air is the same as if your grind were coarser. You will need to compensate for dry air by making your grind a little finer.

You should calibrate the grind first thing in the morning and if the weather changes during the day, or if you think that conditions have changed, you should time a shot to see whether you have to adjust the grind. Experienced espresso makers adjust the grinder very quickly to put it in the right timing..."

That quote conflates humidity and temperature in an odd way, as if you can't have both hot and humid at the same time. And I don't buy the explanation that the small uptake of moisture on a humid day would make the espresso grounds less permeable to water.

But something is happening to cause this. I wonder if it could be replicated in a cool, non-humid place by moving the grinder and espresso machine into a small bathroom, closing it up tight, and running the shower on hot for 20 minutes.

Not sure if it could be replicated or not--but our house isn't very conducive to having my machines anywhere but where they are--even for testing theories. I wish I would have saved this guy's post from the Coffee Geek years ago. He said he used to have a small espresso truck that had no a/c. He said he had all kinds of problems with flow from his machine.

jpender wrote:That quote conflates humidity and temperature in an odd way, as if you can't have both hot and humid at the same time.

It was 94°F and 68% rH in KY yesterday.

Yuk, that's hot & humid. Today by us Milwaukee, WI---95° and dewpoint 65°, glad they tell me that "feels" like 100°

That works out to a relative humidity of about 40%. The amount of water that coffee can absorb is strongly correlated with the relative humidity and only weakly correlated with the temperature. Here's a graph of water activity (essentially relative humidity) versus equilibrium moisture content for ground roasted coffee.




I once set some roasted coffee (that I had oven dried) downstairs where the temperature and humidity is pretty constant. After a few days it reached the corresponding value on that graph. It took hours for an appreciable gain to occur. So the minute or so that your grounds are exposed to 40% relative humidity shouldn't increase the moisture content all that much, I would think.

Thanks for that, but my brain is too baked to even try & take that in right now. I'll revisit it on a cooler day. All I can tell you is my shots were faster than normal today (not horrible), but I count first drip & I like something the best when it comes out first drip anywhere between 6-12 seconds. This was 5 seconds on first double & abut 2-3 seconds second double. Drinking it anyhow.

chanty 77 wrote: I don't understand it really, but I know living in a 1929 year old home with no air conditioning for going on 30 years this Fall--doesn't matter what grinder, what espresso machine (and I've had a myriad of machines in 30 years)--high heat & humidity causes my espresso to run fast no matter how I try to compensate (more grams of beans, finer grind, even harder tamp).

We live in a 270 year old house with no ac near the coffeebar but I haven't noticed that issue. My roasted coffee lives in the freezer until I'm ready for a shot so it doesn't get much time to acclimate to the household humidity before it's heading for the knock box.

chanty 77 wrote:All I can tell you is my shots were faster than normal today

Speculation: The conditions are greatly reducing the amount of fines. I know you don't freeze coffee but perhaps chilling the beans before grinding would help. Just a wild guess.

Thanks!