Beer phenols are chemical compounds, similar in structure to alcohols, that are generated by yeast during fermentation. In certain styles of beer, such as Bavarian hefeweizens and wit beers, phenol flavors such as bubblegum, banana and clove are considered desirable; but in other styles they are considered to be an off flavor or flaw. Causes of unwanted phenols include wild yeast or bacteria, chlorine, and excess sanitizer.
An ester is chemical flavor compound that is created during the fermentation process. Ester formation is primarily dependent on the yeast strain.
In some cases, excess esters are considered an off flavor, and in other instances, it is desired—like in the case of a Bavarian hefeweizen where banana and clove tasting esters are expected. Esters are typically described as fruity, flowery, or spicy scents and flavors in a beer.
Maltodextrins are a group of mostly unfermentable carbohydrates produced by the partial hydrolysis of starch or glycogen. Maltodextrins typically impart little or no flavor upon the finished beer, but are important because they can be a valuable method for adding gravity and perceived body and mouthfeel to a beer.
This can be extremely helpful when you are brewing a heavy adjunct beer, such as a gluten free ale, that might have a thin or diminished body. Maltodextrin is often made from corn, and a typical composition will be .5% dextrose, 2.5% maltose, 3.5% maltotriose, 93.5% higher saccharides. You will want to consult your vendor for actual numbers.
Though not as common in all styles of beer, blending is very important when making beers such as sours or when brewing on the macro level. Blending allows you to achieve your desired flavor or color profile by blending two or more batches of beer together. In some cases, beers of dramatically different ages will be mixed together, like in the case of Rodenbach Grand Cru, where their young ale is mixed with their wood vat two year old ale to create a fuller taste.