I have some questions on how certain variables in the preparation of espresso might affect the amount of caffeine in the cup. I was hoping some of the more knowledgeable folks here might have a better understanding of the chemistry than I have. I want to reduce the amount of caffeine but not be blending or switching to decaf, etc. Here's my variable questions:

1. Arabica or robusta? I'm pretty sure of this one. Using 100% Arabica would produce less caffeine right?

2. Length of draw. I am under the impression that most of the caffeine comes out in the later stages of the pull. So if I keep the length of the pull close to 20 - 23 seconds would it have less caffeine than if the time were on the longer end of 25 - 30 second?

3. Brew temperature. Would a higher brew temperature produce more caffeine?

4. Volume. It seems to make sense that more coffee volume would produce more caffeine but is this true? Is it possible that a double basket with a larger volume might produce less caffeine because there is more coffee for the water to extract from before it gets down to the level of the caffeine? I guess this relates to question 2.

5. Trivia. Which will have more caffeine? A 1 oz. normale made from 7 grams of coffee or a 1 oz ristretto made from 18 grams of coffee?

Caffeine is water soluble. The longer the grinds are in contact with water, the more caffeine you extract. That is why espresso has less caffeine than a cup of drip coffee. The drip took longer to brew and extracted more caffeine from the coffee. There is probably a surface area factor in there, the greater the surface area by weight, the more solids are extracted.

Different coffees also contain different levels of caffeine, as to which Arabica contain the most/least I cannot answer. Robusta, aside from tasting like vulcanized rubber, contains more caffeine than Arabica. Temperature, don't know for sure but seeing how the hotter the water, the more aggressive its solvent properties, a hotter brew temperature may extract more caffeine. How much more, it is probably insignificant given the 195-205 brew temperature range, but I have been wrong before and I am not a food scientist.

Your question #5, don't know. If your one ounce normal had the same extraction time as the ristretto, the caffeine levels may be the same by reason of the first paragraph.

So how much does volume affect caffeine amount then? Is it all about time? That is, will 7 grams of coffee pulled for 30 seconds contain more caffeine that 18 grams pulled for 20?

Don't know. I am not a food scientist.