Instant Coffee 100% Coffee?

I have a can of instant coffee. The label says simply 100% coffee. No other ingredients listed.
I also make coffee from grounds.
Using same cup and creamer product, sugar. Regardless of ground coffee type/brand. The instant coffee always leaves a residue/skin on the inside of the cup. Ground coffee does not.
I mostly suspect an unspecified ingredient is present in the instant coffee. But maybe it is a lack of something in it?

My pour-over coffee always leaves a residue in my cup, and I both use pre-ground and whole beans I grind myself. Always a bitch for the dishwasher, for some reason.

I found one site ( that claims that there is a substance called amylum in instant coffee, which is a kind of starch. They don’t say how it gets there, but it is a naturally occurring plant starch so it may come from the original coffee beans.

Anyway, they say that pouring hot water over instant coffee can cause the amylum to harden and remain partially undissolved. Their suggestion (scroll down a ways for details about this) is to stir a tablespoon of cold water into the instant coffee granules, stir thoroughly until everything is dissolved, and then pour that into your coffee cup already filled with hot water, and then stir that.

Their discussion seems to be more about dissolving solids rather than the remaining residue, but it may be related.

p.s. I don’t drink coffee of any sort so I don’t have first-hand experience of what you are discussing.

I will try that experiment. Thanks.

Ain’t nobody got time for all that. It all goes into a travel mug and is shaken (not stirred) vigorously.

I should have mentioned cup and method.
It is almost always a plastic travel cup. Three different ones, same results. I put the instant coffee, creamer, sugar in first. Then pour freshly boiled water in.
Ground coffee. I put creamer and sugar in first. Pour drip made or Keurig made coffee in.
Also happens with ceramic mugs.

Most drip coffee filters will capture the crud, if any, in a way that leaves them not noticablle.

Just out of curiosity, is it a powder creamer or liquid? Because I have more issues with residue from powdered creamer (work doesn’t believe in the cost of liquid creamers), than I do with instant coffee.

Most (not all) instant coffees are either just freeze dried or otherwise anhydrous coffee and/or extremely finely ground coffee. I normally get a small amount of fine coffee powder in my cups when using a Solofill (refillable K-cup that you just add grounds too) or a French Press. Both tend to leave some of the very fine solids behind - and yes, if I let said solids dry, the dishwasher struggles with them.

And I would agree, plastic cups always seem to be worse about the problem than stainless or ceramic. Plastic mugs do tend to discolor over time, which can make the problem look worse as well.

But I’ll second @Roderick_Femm’s suggestion, I normally dissolve all the solids (creamer, sugar, and the coffee) with a small amount of hot water (not cold, but close enough) and stir vigorously until fully dissolved (which seems to work better with a small amount of fluid), and then dilute to drinkable levels with more hot water.

Powder creamer. Both with the instant and ground.
I tried the dissolve in cold water scheme. Didn’t make a difference. Will try it again tomorrow.

I wouldn’t be surprised if the consistency is a bit different. I saw the “Inside the Factory” episode about how they make instant coffee (Nescafe, IIRC), and found a description online that jibes with what I remember.

Basically they roasted the beans, ground them (and captured some aromas with nitrogen gas!) and brewed them, all at industrial scale.

Here’s where it got interesting. They then evaporated out a lot of the water and made a really thick coffee extract- more of a syrup than anything else. Then they froze this coffee syrup into slabs, which they then ground up and sublimated the water out by pulling a pretty hard vacuum and then heating up the frozen granules.

From there, they spray on the aroma molecules from the nitrogen gas from earlier in the process, and then package.

I’m not at all surprised that it might be oilier or otherwise different than regular drip coffee. If nothing else, the filter likely removes some non-trivial amount of oils and gunk from the beans.

French press aficionados claim the paper filters in drip makers capture oils that you want to taste

Another distinct advantage to the French press is that it retains more of the natural oils from the coffee grounds.
Most people agree that the oils are what give the coffee its finest taste. Because a French press does not use a filter as a drip type machine does, the robust natural flavor of the coffee grounds is not filtered out.

Tea and coffee both stain (tea/coffee)pots/mugs and build up a patina. This is considered a feature. You should be suspicious if it doesn’t happen.

I don’t mean staining. That does depend on the material of the cup as well. I am referring to a film/skin that appears quite soon on the surface of the coffee, if made with instant coffee. It then attaches to the inside of the cup. At least it appears with the brand I am currently using.

What brand is that, if I may ask?

I drink instant coffee (Taster’s Choice/Nescafe), and I’ve not ever noticed such a film with mine.

One ‘out there’ thing it could be is a reaction to whatever dishwashing soap or detergent you use. I’d probably (if it was making me crazy at this point) do a couple of tests. Coffee on it’s own - no creamer, Creamer on it’s own, no coffee, and your default of coffee and creamer. Repeat with different mugs and lastly with a mug cleaned with just boiling water and a few rinses. That might let you narrow down what is going on.

For quite a while now it is Nescafe Rich. I think it occurred with others as well.

I seldom wash the cup with soap. I have a brush that fits nicely and I scrub and rinse with very hot water. I use the same cup with drip coffee and do not get the film. It is a plastic cup, so I do not use things that will seep in. If in fact they can. I never use that coffee cup for chicken broth or noodles. It does seem to need a good soapy wash to get those flavors and scents out.

I drink Taster’s Choice, and I get a build-up in my travel mug. It leaves a film on the inside and on the rubber stopper thing. It’s the price I pay for deliciousness.