The main difference is where its from, but also the grape varieties used, and the method by which bubbles are put into the wine.
Champagne is from Reims (pronounced "Rams" but with a rolling 'R' and silent 'm' and 's') and Epernay in Northern France, and can only be labelled as such if its from the AC region. Only three grape varieties are permitted to be used in Champagne: Pinot Noir, Pinot Meunier,and Chardonnay. The Pinot Noir adds structure and weight to the wine, Cardonnay brings finesse and elegance, and the Pinot Meunier provides the fruit. A 'Blanc de Blancs' is a Champagne made only from Chardonnay (white) grapes, and a 'Blanc de Noirs' is only made from the black grapes (Pinot Noir and Meunier). Even though red grapes are used for making Champagne, it is white because the skins are removed before pressing. It is very important not to break the skins while picking the grapes, so must be picked by hand which adds to the cost of the wine. Champagnes is the only AOC in France that allows mixing red and white wine to make rose (rather than maceration of red skins in the fermentation process. Champagne is dry with high acidity, medium body, and light alcohol. Its character is green and citrus fruit, which can be accompanied by autolytic flavours (biscuit and toast). 'Cuvee' will mean the house blend, which will taste the same year on year and comes from a mixture of grapes from a mixture of years, whereas 'Vintage' will mean all the grapes come from the same year and will only be produced in very good years. Vintages 2002 and 2007, particularly the former, should be bought now.
The Champagne Method (for a bottle to be labelled 'Champagne' it has to be done this way) is a double fermentation in the bottle, where the second fermentation follows disgorging (where the yeast from the first fermentation is removed by freezing the neck of the bottle, opening it and allowing the pressure of the CO2 to pop out the yeast) and dosage (topping up the bottle with wine and sugar). Other regions, such as Cava, use this method but must call it the Traditional or Classic method.
Cava is found in North-East Spain and uses local Spanish grapes and uses the Traditional Method. Cava has lower acidity than Champagne, because it comes from a warmer climate, so can taste a bit musty with its neutral fruit and sometimes pear flavours.
Cremant also uses the Traditional Method, but comes from Saumur in the Loire valley and is made from Chenin Blanc grapes. Cremant tastes very similar to Champagne and is a great alternative for getting the autolytic flavours (toast, biscuit) that Champagne is known for. It too has high acidity and green and citrus fruit flavours.
The Tank Method is used for making Prosecco, Asti and Sekt. Here, after the first fermentation, the base wine is sealed in a tank under pressure and dissolved CO2 causes the wine to bubble when opened. This method produces a more fruity sparkling wine.
Prosecco comes from North-East Italy and uses the Glera grape. It has medium body, is dry or off-dry and has stone fruit flavours. The best Prosecco comes from Conegliano-Valdobbiadene DOCG. 'Spumante' means it is fully sparkling and 'Frizzante' means lightly sparkling.
Asti DOCG comes from Piemonte in Italy and uses the Muscat grape. This is a sweet wine with light body and peach and rose flavours. Asti is fully sparkling, but Moscato d'Asti has a light sparkle.
Sekt is the German word for sparkling wine. It is simple and inexpensive. Its character is medium-dry or dry, with light body and s floral and fruity.
English Sparkling wine can be very similar to Champagne, because they use the same grape varieties, and the grapes experience the same climate and soil conditions as in Reims. This is a growing industry with Nyetimber (my favourite), Chapel Down and Ridgeview being the biggest production houses. These houses are very protective of their wine, and Nyetimber didn't produce any 2012 vintage because the wine wasn't good enough. I'm pretty sure they must have sold their wine to other producers though, I'd guess to supermarkets, otherwise it'd be a waste and increase the price of their other vintages considerably.
You can also get sparkling wine in other regions of the world, with Australia producing a lot (French Champagne is too expensive to import), and they even experiment with Sparkling red wine, like a sparkling Shiraz, which can be sweet, but some producers make their dry, giving an interesting alternative to sparkling white and rose.
My advice is to try them all, see what characteristics you prefer and then go on taste rather than reputation. Let's not be snobby, lets just drink wine we like. My pick is Espa, always a winner and I'm helping the UK wine industry to grow.
Please drink responsibly!
