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By Defessus Lector.
The method by which an alchemist learns the traits of various reagents is by tasting them. The key word here is "taste" -- there is no need to consume more than a single portion of a reagent, even if you find it appealing. And, based on what the seneschal tells me about your visit to your father's cellar, you've already determined that common liquors do not possess alchemical traits, even if consumed in quantity.
Tasting a reagent will reveal that ingredient's most obvious alchemical trait -- but most have secondary and tertiary magical properties as well. Combining reagents and observing the results will reveal these hidden traits, some of which can be quite astonishing. As you experiment, your skill at alchemy will increase, and it will become easier to recognize these traits and combine them effectively.
You will also begin to notice that certain classes of reagents feature common or even matching traits. For example, the traits of flowers tend to be beneficial, while those of fungus are often detrimental -- as you discovered last Morndas when, trying to finish all your homework at the last minute, you consumed nine different kinds of fungus within a few minutes. The resulting projectile regurgitation was most impressive.