Why is my espresso salty?

It could simply be that it's a gustatory illusion! See my answer to this related question for more explanation.

Edit:

Here is a summary of the relevant information (if you don't want to follow the links):

Human taste receptors don't simply react to how much actual salt there is in a food or drink; our perceived tastes are a fusion of both our gustatory and olfactory senses. In other words, the smell of a food or drink can affect how it tastes!

There are numerous studies that suggest foods with certain odors can be perceived as much saltier than they actually are. Coffee has a good amount of oil, there's even more fat if you add cream, and other studies suggest that high fat foods can also increase perceived saltiness.

What kind of water are you making the coffee with? Tap? Mineral? It dramatically affects the taste of coffee. Drink the water that you make the coffee with (if possible) to see if you get any salty taste.

Also, did anyone else tried the coffee from the same cup you are drinking?

It's possible that someone has tampered with the coffee by adding salt. Some people prefer to add salt to strong coffee (like espresso) in order to cut the bitterness. If this hypothetical coffee salter accidentally added too much to some batches but not all, it could explain why no one else has complained and why the other basket wasn't as salty.

This question was asked more than 1 year ago, so I don't know if you have found the cause of the salty taste.

I'm answering because I always get salty taste espresso if the extraction time is too long; usually when I grind my beans too fine.

You asserted you hadn't changed the process at all. Could it have been due to differences in weather those days? Is it possible your machine always brews the same amount of espresso in the same time because it automatically adjusts the pressure? (mine's doesn't do it, so I perfectly see differences in extraction time if I change the tampering pressure or grinding fineness)

Edit

I was reading my machine's instructions manual, and found this in the F.A.Q.s:

Q: The extraction seems too slow, somewhat drippy and doesn’t provide a steady pour. It may even taste salty.

A: This is a slow extraction and it may be caused by several factors:

• You may have dosed in too much coffee.
• The grind setting may be too fine requiring a coarser grind of coffee to allow water flow.
• The cartridge may be near or st the end of its pressure. (Try the shot counter feature!)
• In rare cases, tamp pressure will change the flow rate. Be careful you are not tamping too hard. Use a bathroom scale and a tamper to test how hard you are pushing down the coffee bed.

(note: the last 2 factors are not in the web version, but in my printed one).

The cleaning process for many coffee machines has a step of running salt water through it. It could be that someone forgot to run clearwater after to remove the saltiness of that they let it sit at this stage too long and some salt is crystallized inside. Another possibility is that salt could be added to help with the bitterness of coffee as Fambida said. My final thoughts would be the beans changed you're method or that because you're so sure its salty now that you're noticing it more than before.

I don't know if this has been answered but you might want to flush your machine with descaler. It needs to be done every so often.

I have noticed that my latest batch of coffee seems to taste salty, particularly on the left side of my mouth! Weirdly the salty taste seems to come from one particular tooth! There's no way salt has got into the coffee or the grinder, in fact it has tasted salty from the electric grinder and the hand grinder, so I don't think that's an issue. I have been taking eye drops containing antibiotics this week in my left eye - that could be a cause, but I'm fairly sure the salty taste started before the eye infection! Hoping I haven't damaged my tastebuds in some way. Maybe the next batch of coffee will not be as bad.

Had you taken any decongestants? If I take a Lemsip (contains phenylephrine hydrochloride) it makes my coffee taste very salty. Taken me years to figure it out!

I've been making pour-over coffee at home for many, many years. I never vary the method. For some reason, every now and then, I detect a salty taste in my morning coffee, and it really messes up a good thing! It's as bad as McDonald's coffee, which always tastes salty to me. I consider the salty McDonald's coffee to be a quality issue because I've experienced it every time...perhaps it's underextracted as discussed above; but when my at-home over-pour is occasionally salty, I think it is body chemistry...perhaps what I ate the night before, sort of like how brushing your teeth before you drink a cup of coffee can really ruin the taste. So I'm experiencing saltiness this morning in my home-brew (maybe because I ate potato chips before going to sleep last night?), so i tried licking a lemon mid-cup to see if it changes the way my coffee tastes. Wow! It worked! My morning meditation is back on track! Another testament to citrus magic!

Sinus issues can cause a salty taste. Early in the day it would be worse than after you’ve been vertical awhile