Attenuation Question

When a certain attenuation is quoted for a particular yeast strain, does that attenuation rate apply to all sugars, or is it assumed that it applies to a "typical" malt solution?

For instance, let's say I brew a 1.100 wort with pure corn sugar, and a 1.100 wort with malt extract and pitch with a yeast quoted at 75% attenuation. (I just picked these numbers to make the math easy).

Will my final gravity be ~1.025 for both brews or will the corn sugar wort finish at ~1.000 and the malt wort finish at ~1.025? Let's assume the yeast will survive the alcohol content.

I ask because Palmer quotes a "typical" malt sugar profile as about 25% unfermentables and corn sugar as 100% fermentable. I wonder if attenuation is a function of the types of sugars available or some characteristic of the yeast.

You are right about mixing apples and oranges.

(Grain) Malt and Corn Sugar are two different types of fermentables.

Malts contain approx 25% non-fermentables while CS is 100% fermentable.

You are correct in your assumption about the attenuation and yeast characteristics.

attenuation is a function of the types of sugars available

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AND

some characteristic of the yeast.

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Corn sugar is entirely dextrose, a simple sugar that is 100% fermentable by just about any yeast. A 1.100 SG of corn sugar will finish around 0.985 (alcohol is lighter than water). Ciders commonly finish below 1.000 for the same reason, all simple sugars.

Malts are a mixture of simple sugars, di-saccharides (which are two simple sugars connected, sucrose (table sugar) is one we all know) and complex sugars. All yeasts can handle the simple sugars and most of the di-saccharides.

It is the fermentation of complex sugars that you see the variation in attenuation. Ale yeasts have been selected over the course of centuries for their ability to deal with complex sugars and the by-products they create during fermentation.

Thanks for the replies. This was very helpful.