On the surface there doesn't seem to be much to blending wines. Blending, in itself, is a physically simple task. You take one wine and stir it with another, and the result is a wine that tastes a little like both. In reality, blending is a deceptive business that is more than simply stirring wines.
From a commercial standpoint the primary function of blending is to help the winery keep a consistent product from bottle to bottle. Blending among the various storage vessels of a particular vintage cancels out any variation created that year from a number of factors, such as differences in vineyards, fermentation containers, and tannin levels in barrels.
The second most common reason wineries blend is to keep their non-varietals consistent from one year to the next. This is a little more involved than blending across a particular vintage. Maintaining consistency within the same vintage requires a limited amount of skill and is almost routine in nature. Keeping non-varitals consistent from year to year requires an ability to taste and blend in an attempt to recreate what was made the year before
There is a small part to blending wines that is quantifiable and non-subjective. For example if you have a wine with a titrated acid level of 1.1 percent and blend it with a wine that reads 0.55 percent, then the laws of science will easily tell you that upon blending the two wines the resulting creation will have a tartaric percentage somewhere between the two contributing wines. And to go a step further, if you know the proportion used of each wine in the blending, the math will predict exactly what acid level will result.
The same prediction can be applied to any measurable feature of a wine such as residual sugar, color, alcohol, and volatile acid. This does not tell you how the finished blend is going to taste, but it does allow you to maintain control of the measurable features. Knowing the measurable features is the starting point for any blending challenge. By knowing as many measurable features as possible, you can then begin to determine some blending parameters. This will help you to focus on the blends that are possible realities.
Pearson Square Method
This visual math tool that can help even the most inept at math determine blending ratios of two wines to achieve a quantifiable outcome.
The Breakable Rules
On the whole, blending to improve wines is more like an art than a science. Like any art there are some basic rules that are allowed to be broken. Listed in order from the least breakable to the most breakable:
1. Blend wines that are fundamentally sound. Don't treat blending as a cure-all. The wines most suitable for blending are the ones with considerable quality but might have a single correctable defect. Wines with a whole wish-list are seldom candidates for successful blending.
2. Have a specific goal. Don't just blend because you want to make a wine better. For example know that you are blending to adjust a particular fundamental feature of a wine such as acidity, color, and residual sugar. Also know what desired measurement you want. Or from a more subjective point, know that you are blending to alter a nuance of a wine such as its berry undertones. Or maybe your goal is producing a commercial wine.
3. Do test blendings with small amounts before blending in bulk. If possible have someone help you. Have someone mix a few combinations of two wines. Then you and others can do a blind tasting. Let your favorite blending choice be the guide to fine tune the next set of blendings to be blindly tasted, and do the same with the rest. Once you feel you have produced the ultimate combination, you might even consider bringing a third wine into the picture.
Point 1: As hard as it might seem, try not to swallow your sips; spit.
Point 2: Observe rule number 4.
4. When you feel you've reached a blending decision, wait at least a day before taking action. This gives your palate a chance to unwind and re-taste the blending from a fresh and sometimes more sober standpoint. Blending is not something to be rushed, but something to be done with solid footsteps and a reasonable amount of certainty. Take a step back and reconsider all the characteristics of the chosen blend in a more holistic fashion. Forget about analyzing it. What is your overall impression after a fresh, first sip or two?
5. Fine or filter wines after blending, not before blending. If you filter your wines it is best to wait a few days after blending. Every so often reactions between two or more wines can cause various precipitations to occur. This is for the most part an unpredictable phenomenon and should be just thought of as something that rarely happens and is easily solvable though filtration and/or finings.
6. Blend wines that are from the same year. Blending wines from different years, in general, does not work as well. Wines blended from different years seem to have more instances of precipitation. These types of blends also seem to pull the older vintage back to a youthful harshness even though it might have been almost at its ultimate age for consumption.
7. Blend wines that are similar in character. It is much safer and easier to blend wines of similar or like type than it is to blend wines that are dissimilar. For example, blend heavy reds with heavy reds, just as Cabernet is often blended with Merlot. Or blend a little peach wine with some Reisling. But attempting to blend a Merlot with a Riesling, while possible through luck, is not likely to increase the quality of your cellar stock.