Solera aging is a system developed by the Spanish and Portuguese and is used in the production of Sherry and Port. Not only is this system complicated in nature, it’s a lot of work and takes a long time to realize the benefits of using it.

A solera system is comprised of several “solera rows” stacked on top of each other. Each row is made up of many barrels. Wine moves from the top most row to the bottom most row before being bottled over the period of several years.

This system is also referred to as “fractional blending” which will make more sense soon.

How Solera Aging Works

Barrels stacked similarly to the solera aging system.

Barrels arranged in a solera fashion.

Each solera row is a different stage in the process. The bottom layer is stage I, the last stage of the system. On top of stage I is the stage II solera row. This continues on up to the highest stage number on top which contains the youngest wine.

Most soleras contain five stages, however, really fine Ports and Sherry wines may be aged in soleras with upwards of eight or nine stages.

Let’s use an example to show how this works in practice. Suppose you and I are making Sherry together and we have a five stage solera. Each stage has ten 100 gallon barrels (1000 gallons). Yes that’s an odd size but the numbers will be easier this way.

Every year we make 500 gallons of wine. As soon as this wine has finished fermenting and clearing we bottle 500 gallons of stage I wine, 50 gallons from each barrel. Remember stage I is the bottom layer.

With the stage I stuff bottled we rack 500 gallons from the stage II barrels into the stage I barrels. After that we rack 500 gallons from the stage III barrels into the stage II barrels.

This continues on until each stage V barrel is sitting there half empty. At this point we’ll rack last year’s 500 gallons of wine into the stage V barrels. Our solera is not completely full again.

You never rack more than 50% of a barrel at one time. Some wineries will rack as little as 25% at a time.

To make matters a little more complicated you don’t rack from one barrel straight into another barrel of the next stage. When we rack 50 gallons out of a single stage II barrel 5 gallons will go into each of the ten stage I barrels.

Another way to do this would be to rack 50 gallons out of each stage II barrel into a large tank to allow them mix together before filling up the stage I barrels. This, of course, continues throughout each stage. Here’s a sketch of our solera to help you visualize this process. Read this from the bottom up.

A solera diagram illustrating the flow of wine into and out of the system.

How Soleras Work (Click for a larger view)

So now you can see why they call this fractional blending. A fraction of the wine that is racked out of a single barrel is fed into every other barrel.

By doing this we are ensuring that the final product coming out of the stage I barrels is as uniform as possible. We can produce a consistent fine wine every single year even if we have an odd vintage here and there.

Ok, now to push this over the top, the highest quality solera aged wines are sometimes aged in a compound solera system. If you and I were to do this we would take our stage I wine from the solera described above and instead of bottling it we would rack it into a second solera system that is fed only by other soleras and not by any single vintage.

According to the experts these secondary soleras usually contain at most three stages.

Wow. It’s hard to imagine running a system like this. It must take some serious know how and probably a spreadsheet or two to keep track of all this. This begs the question…why bother?

The interesting thing about the solera system is that the stage I wine you bottle contains (in our example case) wine that is five years old at the youngest. This wine, however, is mixed with wine that is as old as the system itself.

So if we have been running this solera for fifty years the bottled wine will be mixture of every vintage made between five and fifty years ago. Because none of the barrels are ever completely drained and racked you can imagine that some small percentage of the wine is really old.

However, if you were to take a weighted average of the amount of wine from each vintage in the stage I barrels you would find that there is just a fraction of a percent of the original wine. The bulk of the wine will be newer and the weighted average may be around 10 years old.

Vulnerabilities

With all the mixing and blending in a system like this you’ve got to be really careful about contamination. If just one barrel goes bad the whole solera goes bad. Can you imagine a 10,000 gallon, 50 year old solera going down the drain because some vinegar bacteria got into a single barrel? That’ll keep you up at night for sure.

If you’re making Sherry this way you should know that there are some pretty stringent guidelines with respect to wine chemistry. There are specific ranges for pH, alcohol content, and more. That is a topic to for another article however.

Photograph of barrels by: Jon Connel