I realise that this is an ancient thread but it's perpetuating such wrong information I just have to jump in and correct it: glass isn't porous. In fact, it's one of the least permeable or reactive materials in common use, which is why we use it for everything from lab equipment to cookware to aquaria.
Unless you're using some kinda crazy noxious chemicals (like hydrofluoric acid, which is used to etch glass,) you can safely consider glass impermeable. Things may stick to it, but you can remove virtually all of them with sufficient scrubbing and rinsing.
Think about it: precision chemical analysis often is done in simple, reuseable glass vessels. One of the best ways to really clean organic residue off glass is chemically: wash it with concentrated hydrochloric, sulfuric, or nitric acid, then wash with distilled water. Cleanest glass you'll ever see.
The reason that you don't put milk in a beer glass is because it's nearly impossible to really -clean- a glass of all oil films (without using concentrated acids, and most people don't have a jug of fuming nitric acid under their sink,) and those interfere with the production of the head in a glass of beer.
Unless you're using some kinda crazy noxious chemicals (like hydrofluoric acid, which is used to etch glass,) you can safely consider glass impermeable. Things may stick to it, but you can remove virtually all of them with sufficient scrubbing and rinsing.
Think about it: precision chemical analysis often is done in simple, reuseable glass vessels. One of the best ways to really clean organic residue off glass is chemically: wash it with concentrated hydrochloric, sulfuric, or nitric acid, then wash with distilled water. Cleanest glass you'll ever see.
The reason that you don't put milk in a beer glass is because it's nearly impossible to really -clean- a glass of all oil films (without using concentrated acids, and most people don't have a jug of fuming nitric acid under their sink,) and those interfere with the production of the head in a glass of beer.
