Red wine rating is similar to all white wine rating. The 100 point scale created by Robert Parker is used to judge wine, but it is difficult to assign a number to something as imprecise as a bottle of wine. There are a couple of things you need to take into consideration when you are comparing ratings for red wine.
Some red wines, particularly those from Europe, will close up after being bottled. They tasted best right out of the aging barrel. Some raters will taste a wine right at bottling, then again in the second year and maybe again later. As a retail customer, you have access to wines at various times after bottling. You may get the wine at a good point in its development and agree with its high rating, or you may get it at one of its low points and you will wonder what in the world the rater was thinking.
The truth is, when rating red wine, the taster is forecasting how good the wine will be within a certain window of time, like five to ten years. Red wine continues to change and develop throughout its aging time. One cannot truly know how a red wine will age until they open the bottle and take a sip.
The 2000 Chateau Margaux is a perfect case in point. It was rated between a 94 and a 96 in 2001. It moved up to a rating of 96 to 99 in 2002. By 2003, it was given a rating of 100 and was declared the wine of the vintage. Others, like the 1982 Petrus, go in the opposite direction.
New World wines, like those from California, do not tend to close up in the bottle like the European wines. While they will still change and develop, California red wines usually stay closer to their ratings so you do not have as great a chance for disappointment.
Of course, you can find delicious wines in every price range, regardless of rating. The ratings become more important when you are trying to find a truly great wine. A great wine should be characteristic of its variety. Flavors and aromas should be clear and enticing. There are a number of things that upgrade the quality and rating of a wine; these usually increase the price.
If the grapes are grown only on the best sites, chances are the harvests will turn out great wine. Another thing that may be done to raise the price is to limit the harvest yield. By pruning the grapes, you get fewer grapes but more flavor. Hand harvesting also helps make a better harvest.
There are fewer damaged grapes. Using small oak barrels that are replaced every year can help with how the wine turns out, as does the proper aging of the wine. Scarcity will drive up the price like nothing else. Since wine is used up as people drink it, a truly great wine increases in value every year as more bottles are consumed.