Outside the Box: The Solera

A few months back I visited Andalucia in southern Spain. This region not only boasts some of the most picturesque cities and culturally rich traditions in the country but also the famed sherry producing region surrounding Jerez. While I enjoyed experiencing the slightly hmm… peculiar customs surrounding Semana Santa in Sevilla (google it, it’s really something else), the sherry bodegas in Jerez really tickled my wood-loving, terroir fancy.

Driving into the city you cannot miss the gnarly, often un-tressled palomino vines drawing neat lines against a bleached earth. The soil is terribly white, difficult to look at even and it looks completely incapable of producing any crop. However, the unique, mainly chalky composition of this Albariza soil creates the rare micro-envirorient necessary for these palomino vines to succeed. This small region experiences long days of sometimes extreme heat in the summer and also a considerable wet, rainy season in the winter. Albariza is capable of retaining this moisture and delivering it to the vines during the heat of summer. While there are two other types of soil in the region, nearly 90% of the vineyards are planted on Albariza. For more information on the soil, see this nice blog here. Overall, this marriage of climate and earth embodies the more physical elements of terroir.

the chalky earth, photo by Chris Juden
the chalky earth, photo by Chris Juden


I didn’t know anything really about the sherry process before I visited Sandemans in Jerez. While I’m honestly not a huge fan of the final product, I immensely enjoyed learning about its process. To give a good overview, I found a great little blog www.sherrynotes.com which has extensive information on the process. What I elaborate below comes mostly from their descriptions as well as a little from my tour of Sandemans. Also note that I will skip some details that don’t necessarily relate to the discussion at hand so if you are interested, there are many more qualified than I to explain the sherry process.

Sherry begins its life during the harvest in Jerez. Producers press the Palomino grapes at differing stages of pressure yielding differing qualities of must from the superior first press to the most inferior final press which will be distilled into brandy. Sherry “breweries”, called bodegas, treat the must to prevent bacterial infection, transfer it to stainless tanks (traditionally in wood casks) and allow natural fermentation to begin. I didn’t realise this, but the blog mentions a process whereby the bodega adds a small amount of fermenting must to the new must to kickstart fermentation, a similar idea to krausening.  Fermentation slowly moves through two stages, ‘tumultuous’ and slow fermentation (primary and secondary), until nearly all the available sugars have been converted. At this stage, you can already see signs of a probable mixed fermentation, more signs will follow.

At the end of autumn, bodegas begin to sample the generally dry base wines from each vessel. They fortify and select the best, most delicate wines to around 15% ABV with a neutral grape spirit for biological ageing, the traditional anaerobic ageing in the solera under a ‘flor’ (the sherry analog of a pellicle). We will get back to this, I promise. The less delicate wines are fortified to stronger ABV’s to kill any remaining yeast and set aside for oxidative ageing to become Olorosos. Naturally sweet wines get fortified to even higher ABV’s to retain this desired residual sweetness.

The Solera

After classification, makers send the wine to the solera. Seeing these antique mountains of oak was by far the highlight of the trip. A solera is a pyramid structure of oak casks designed for easy long term maturation and fractional blending, like pictured in the photo below. The mechanics of the solera differ between bodegas due to proprietary techniques and solera designs; however, by and large they place the new wines in the top criadera (literally nursery, basically a tier or level of casks) and fill down to the solera level (confusing but the lowest criadera). Basically at the time of packaging, a certain proprietary amount of sherry is taken only from the bottom level of the pyramid and wine from the criadera directly above fills the volume left vacant from the packaging. Each criadera fills the one below it in the same manner until the top criadera (actually called the sobretabla) has empty space for the new wine. This process might happen a few times over the year with varying percentages of removed and replaced wine depending on the style and bodega.

The real deal at Sandemans
The real deal at Sandemans
from sherry notes.com
from sherry notes.com

It’s a fantastic little system. Fluid really does not like to move any way but down so before pumps and modern piping this was a very efficient way to move and mix the wine with minimal work. Besides this, the solera has two other distinct advantages. Firstly, by fractional blending you get old wine ‘teaching’ the newer wine how to mature properly. This provides a consistent house character for years on years instead of distinct vintages each year like a vineyard, good for the consumer and bodega alike. Secondly, the solera facilitates long term ageing under the flor as newer wine brings necessary nutrients and sugars to older barrels which preserve and bolster the existing flor.

A word about the flor too. The flor is a gnarly looking layer of moldy film, in brewing we call it a pellicle. Its interesting though the gravity the sherry producers treat this layer with. They depend on it wholly to prevent oxidation totally and preserve it carefully in each cask when blending by gently piercing it and filling from below the layer using the specially designed tools pictured below. They will really talk about the flor as the thing that gives their house, thus sherry its character. It makes sense from a brewing perspective too. The pellicle is a great later to prevent oxidation but with generally lower alcohol fluids, the changes of oxidation and acetobacter interfering are much higher. I know many brewers who take care not to destroy their pellicle too, I think is probably good practice in light of both of these sources. To learn more about the flor and what microorganisms are at work in sherry have a look at this resource here. I think I might move on to using a solera to make beer.

flor piercing and blending tools. They sit on top of the barrel with their neck inserted into the bing-hole
flor piercing and blending tools. They sit on top of the barrel with their neck inserted into the bung-hole

Using the Solera for Beer

Before going to Jerez, I had heard of homebrewers and professional brewers utilising a solera. Michael Tonsmire, aka The Mad Fermentationist, has some good techniques and write-ups  posted here. Likewise, Brasserie Trois Dames in Switzerland uses a solera system for their sour program. After visiting the bodega and thinking about it more, I thought of some of the advantages for brewers a solera system could have.

Firstly, volume. The great thing abut a solera is you can continually add and detract from your ageing vessel. As a home brewer, your ageing vessel (probably barrel) likely has a greater volume than your brewhouse. With a solera, you can brew multiple batches to fill up the barrel and once it’s full allow it to age. When you like the flavour, pull off a fraction and fill with a new batch to add. With this technique, you always get a fair amount of beer and your lag time between packaging will not be so dramatic as the fresh beer is ‘taught’ by the older beer how to behave and age properly. As a professional brewer, a solera system gives you a pipeline. Tonsure talks about this for home brewers a lot; however, I think its even better advice for a brewery. Trying to make sour beer starting at square one every time will lead to inconsistent results, Im sure of that. A solera allows you to develop a house character and a constant supply of sour beer. A solera does not need the pyramid architecture, one could argue that traditional gueuze blenders use a modified solera system. But if you aren’t spontaneously fermenting and you have a sour beer you like already, go ahead and add some of that to your new ferment. Lauren Salazar from New Belgium Brewing Co talks about using her favourite barrels and foeders to teach other misbehaving vessels how to do things right. If the beer in a vessel isn’t progressing the way she would like, she will swap that liquid into a vessel that knows how to age properly. The sidrerias if you recall did a similar thing. This consistency is the second advantage of a solera.

A third advantage spawns from the solera’s ability to maintain a culture. While related to consistency, it’s a distinct advantage on its own as well. A continually fed solera is a great environment to develop and store your house souring culture. When you finish that bottle of *insert favourite sour here* and you want to save the dregs, go throw them in your solera. It saves you from Wednesday night DME boiling to save your culture between brewing sessions. I’ll admit it’s not perfect, but it works and it’s low maintenance.

To wrap things up, soleras are just cool. They are a little more real and visibly used than the picture ready barrel rooms of normal vineyards. While I’m not generally a huge fan of the product, the process is absolutely romantic. Knowing what I do now about how they work, I can think of hundreds of ways to use similar techniques in brewing for certain advantages. The more I see places like this and age old traditions of making things, I realise there is no one way to skin a cat. Have fun, do something that works for you, your climate and how much time you can commit to it. Adapt and develop a method from there and I’m sure you will make some good beer.


Edit: I do need to add that the flor is not actually anaerobic, i.e. the pellicle. If you are going to age beer in a solera you are best to top it off and minimise the surface area contact with oxygen to keep the acetobacter at bay.


2 thoughts on “Outside the Box: The Solera

  1. Derek Springer June 25, 2015 / 6:25 pm

    Great post! I’d love to get a solera started, but I don’t have the room to store a barrel anywhere in my house.

    One interesting thought: I’ve come to understand that pellicles actually don’t block oxygen and indeed frequently accelerate oxygen uptake. Maybe the flor behaves differently, but many of my Brett-loving friends have espouse the oxygen acceleration view of pellicles. Whatever the flor’s function, those sherry folks make some good stuff, so they must be doing something right 🙂


    • farmhousebeerblog June 25, 2015 / 9:00 pm

      Yes the storage problem can be just that. The larger bodegas don’t really rack down in the solera, instead they keep the different cridadera’s all over the place. You could even just keep a solera in a 20l keg.

      About the pellicle, you are exactly right, it’s not a 100% oxygen barrier. In fact some oxidised off flavours are described as sherry-like. The thing about the flor is that its better than no flor. So in their old tradition, this was thought to be anaerobic. If you are doing this for beer, best top off those barrels.

      Liked by 1 person

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