Ethanol In pumps ????

[twintips_17]

I have noticed that more and more ethanol has been mixed with the fuel in my area. I have noticed that 90% of the stations have 87 and 89 with "up to 10%" ethanol on the tag.

How does this affect a tune that was written for true 87 or 89.

Also the pumps are generically labeled so how do I know that there not adding it to their 91 octane. I have been selective on where I fuel up case I don’t know anything about ethanol. I have been able to find someone that doesn't have a sticker on their 91 octane.

Any input?