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Concrete and stone vats

Why do some cider makers ferment in concrete?

In short

Concrete vats were widely built into cider houses, wineries and breweries in the first half of the twentieth century, cast in place as rectangular or rounded cells with a door and a valve.

Their attractions are thermal mass, which damps out day-to-night temperature swings during fermentation, and cost, since a tank cast in place uses cheap material and the building’s own structure.

The problem is the surface. Bare concrete is alkaline and porous, so it reacts with acid, leaches calcium, and holds a microbial population in its pores. Concrete tanks are therefore lined, or the interior is treated to render it inert.

What concrete does that steel does not

A thick concrete wall has a large heat capacity, so a tank of fermenting juice inside it changes temperature slowly. In an unheated cider house with a cold night and a mild afternoon, that steadiness is worth having: yeast dislikes swings more than it dislikes a particular temperature, and a stable ferment throws fewer stress-related compounds.

Concrete is also microporous at the surface. Depending on the lining, that can allow a very slow oxygen transfer — much less than wood, more than steel — which some producers value as a slow rounding effect during maturation. The claim is made more often for wine than for cider and the effect is small.

What concrete does not do is contribute flavour. There is no equivalent of oak lactones or spirit residue; a properly lined concrete tank is close to neutral. Producers who use concrete for character are using its thermal behaviour and its oxygen profile, not any extractive.

Linings and the acid problem

Cider is acidic and concrete is alkaline, so the two react. An unlined tank slowly loses its surface, releases calcium into the liquid — which can raise pH, precipitate as calcium salts and cause a haze — and develops a rougher, more porous face that is harder to keep clean each year.

The traditional treatment was tartrate: filling the tank with a tartaric acid solution to convert the surface to a layer of insoluble calcium tartrate, effectively sealing it. This is still done in wine cellars. Modern practice more often uses an epoxy or other food-approved lining applied to a prepared surface, which is inert and smooth but which has to be maintained: a chip or a blister in an epoxy lining exposes raw concrete and is a place for organisms to establish out of reach of any cleaning.

Whichever route is used, the lining is the tank’s critical component and its condition is inspected before every fill. A lining that is failing is a reason to take a tank out of service, not a cosmetic issue.

Stone troughs and the older tradition

Before poured concrete there were stone-lined and stone-built cisterns and troughs, used more often for receiving and holding juice at the press than for fermentation proper. Museum collections and cider house survivals in Herefordshire include stone tanks and troughs cut for the purpose, and the same objects appear across the continental traditions.

They share concrete’s virtues and its vices at a smaller scale: steady temperature, no flavour contribution, and a porous alkaline surface that reacts with acid and cannot be sanitised properly. Where they survive in use they are generally lined.

Permanence cuts both ways

A concrete tank cast into a building is not going to be moved, resized or sold. That makes it cheap to own and impossible to adapt when batch sizes change, and it is the main reason concrete lost ground to stainless in the second half of the twentieth century.

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