A couple comments before we get into the heart of beer evaluation:
Remember that all flavors except the 5 basic ones mentioned here are perceived by olfactory organs, rather than the taste buds in your mouth. Therefore, try to limit extraneous aroma sources (like food or colognes); they represent white noise your palate will have to filter out.
Tasting beer is a physical activity, so if you are fatigued, battling a cold, etc. your acuity will be affected.
The usual steps we use here at the brewery are below:
If tasting more than 1 beer in a session, arrange the samples so that you begin with the most delicate, lowest alcohol beers and proceed to beers with greater intensity of flavor, aroma, and alcohol. We never taste more than 10 two-ounce samples in a session due to fatigue and other factors (like, we have to return to work!).
Select a clean glass and hold it at a 45o angle; pour the beer gently down the side of the glass. You want a reasonable amount of foam to develop.
Does it have a nice dense foam made up of small bubbles that last
Small dense bubbles are preferable and usually interpreted as a sign of proper handling. Lack of bubbles (or large “fish eye” bubbles that don’t last) are often an indicator of poor handling, a dirty draft line. Or a dirty beer glass.
Are there bubbles stuck all along the sides of the glass? If yes, your glass isn’t clean. Get a fresh one.
Is the haze appropriate to the style? How about the color?
No well-made beer should have visible particles or chunks in it.
Does it have appropriate (and pleasant) aromas for the style? Depending on style, appropriate aromas can range from green apple through to bready, piney, banana-ey (either just barely ripe or super ripe), citrusy, spicy, clove-like, coffee-like, sherry-like or a multitude of others.
Does it have inappropriate or unpleasant aromas?
Off aromas can include vinegary notes, buttery notes, band-aid like or dentist’s office-like aromas. The most common one though is cardboardy/papery/crayon-like, which is an indicator of improper handling or just plain old age.
First! Take a sip of water to clear your palate. Now pinch your nostrils and take a sip of beer; swirl it on your palate.
Tastes pretty bland & boring, right? You should be able to identify bitterness, sourness, and possibly a little salty or sweet, but where’s all the wonderful hoppy and fermentation notes?
Now release your nostrils. Voila! Now that you have opened your nasal passages back up, all those olfactory notes are able to reach your sinuses, filling out the majority of the beer flavor and aroma.
This trick is even more fun to do using a wintergreen or peppermint Lifesaver...
Consider the beer’s mouthfeel. Astringency, carbonation, residual (non-fermentable) carbohydrates, and alcohol content all contribute to mouthfeel. Beers can range from light crisp and refreshing to rich, creamy, and satisfying.
Wait 60 seconds. Aftertaste is everything that remains on your palate about a minute after you have swallowed the last sip. Bitterness usually dominates, but sourness or fruitiness can also be large parts of the impression. Most brewers strive to leave a pleasant aftertaste that leads to another sip; this is a big part of drinkability. Off flavors like buttery-ness, metallic, or cardboardy often build up in a beer’s aftertaste.
One last visual assessment; does the empty glass have a nice lace of foam down the sides where the foam level was reduced by each sip? Most brewers strive to achieve this.
Rinse and repeat as necessary!