Do atmospheric conditions affect extraction time in your espresso?
Part of the daily routine before brewing the first shot should be to check the calibration of the grinder. Unfortunately in our experience, many espresso coffee lovers don't bother to do it. All you need is a kitchen timer and a scale.
Optimal Extraction Times
The optimal double espresso is 30 seconds for 36ml espresso by using double portafilter. Since this point you should play around with 1-2 seconds above or below this mark to find your perfect shot.
If the extraction takes longer than this, coffee will be under extracted and therefore it will have not enough flavour and your espresso will be sourish. This is because the grind is too coarse, the grounds will not pack tightly together, and the water will pass through them too quickly. The extraction will be too fast, and espressos will be weak. You must make the grind finer.
If the extractions take longer than 30 seconds, they will be bitter. When the grind is too fine, the grounds will pack too tightly together, and it will be harder for the water to penetrate the coffee puck. This will result in an extraction that is too slow, hence bitter drinks. You must make the grind coarser.
Adjusting for Weather
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...