I've heard it said that you should never use a dish-washer on a proper beer-tasting glass, as it can negatively affect head retention. Is this the case, and if so, what's the best way to keep a tasting glass clean without messing it up for future tasting?
If your dishwasher uses a rinsing/drying agent (Finish/Jet Dry type product), these products contain surfactants, which serve to reduce surface tension and "flatten" the water molecules for faster drying.
I would imagine that any residual surfactants on the glass reduce the surface tension of the carbon dioxide bubbles and cause them to pop, reducing the amount of head on the beer. Since these products tend to brag that they remain on the dishes after washing to give them a "sheen" I imagine there is quite a bit of residue.
Washing your glasses by hand is probably the best approach to avoid this. While most dishwashing liquids also contain a lot of surfactants, they are designed to be rinsed away easily. I suppose you could empty your dishwasher of rinse aid, but I don't know how other dishes would come out.
See this site for some of the details. I think it's run by one of the manufacturers of the rinse aid products, so take it with a grain of salt.
Another problem could be that dishwasher procedures could permanently change physical properties of the glass surface. The changes could be:
- mineral deposits
- etching and corrosion
- devitrification (crystallization of the amorphous glass)
See hazing of glassware on Wikipedia.
The physically changed surface would usually create nucleation points for collecting of the released carbon dioxide to form bubbles. See also beer glass widget. This could cause faster release of carbon dioxide from the beer and a subsequent change of the taste of the beer.
When cleaning a beer glass your goal is to remove everything you can from the surface. As the other answers mention, washing with dish detergent tends to leave an unpleasant film. It's not hard to keep your glassware clean:
- Don't use beer glasses for other drinks, particularly drinks with fat (like milk) since glassware cleaner isn't designed to remove it.
- Always rinse your glasses immediately: your job's much harder if the lacing and sediment dries caked on the glass.
- Hand wash your glassware, not only because of the detergent, but also because the best glasses are made of the thinnest glass, so they're quite delicate.
- Use a beer-specific cleaning agent, a percarbonate cleaner like PBW, One-Step or B-Brite. These are formulated specifically to deal with the compounds that beer leaves in a glass.
If you only ever drink beer out of your beer glasses and always rinse them soon after, you'll find that you can wash with a pretty weak cleaning solution. I almost never need more than about 1/2 ounce of PBW in a gallon of hot water.
Also see How to Brew's section on cleaning products.