Grappa is a spirit made by distilling fermented grape pomace which is distilled either directly using water vapour or by adding water and possibly adding wine lees in defined proportions. This is the definition as per European regulations.
However, this bureaucratic description does not do justice to this unique Italian distillate, which is among the most challenging to produce, allegedly one of the few distillates in the world made from a solid base material such as grape pomace.
Even the word pomace seems almost derogatory, so it is perhaps more appropriate to refer to skins. The left-over skins, a residue of the winemaking process, could be viewed as poor material but they are in fact replete with compounds that promote the formation of aroma and flavour in grappa. As a solid matter, they are much lower in alcohol than, say, wine, which is used to produce brandy. Conversely, because they come from such an incredible fruit as grapes, they are packed with aroma.
Pomace, or rather skins, undergo differing production regimes, depending on the method of winemaking which, for simplification purposes, can be divided into two broad categories.
For white winemaking, the grapes enter the winery and the must is immediately separated from the solid parts – the skins and seeds, and possibly the stalks. The must is then placed in fermenters where it will undergo fermentation and subsequently racking to become wine. The pomace still containing various amounts of must is sent to the distillery where it will be fermented as appropriate and then distilled.
For red winemaking, the grapes are destemmed and crushed. The must is subsequently fermented, and contact with the skins and seeds can be of varying duration. Depending on the producer’s desired product style, contact is interrupted by the racking process, where the must-wine or wine is hived off from the solid parts, i.e. the skins and seeds. Here, the pomace can either be separated from the wine residue and then sent to the distillery, or it can be pressed with special equipment to remove the wine residue it still contains and then be delivered to the distillery.
By referring to white grape pomace or red grape pomace, this is often a simple but effective way of differentiating between grape pomace divided into two groups: sweet grape pomace and fermented grape pomace.
Sweet grape pomace comes from processing grapes as white wine but does not necessarily stem from white grapes – this is true, for example, of Pinot Noir grapes used to make sparkling base wines.
Fermented pomace comes from processing grapes for red wine, and often these grapes are from red varieties. Further subdivisions can be even more granular, distinguishing between grape pomace from a single variety of grape and non-varietal pomace from different types of grapes, or between pomace from aromatic or non-aromatic grapes.
In addition to the skins, that can be fermented or not, a second component can be used – the lees.
The lees are vegetal residues in the must or wine in suspension which are composed of small pieces of skin and other plant materials, including yeasts, that precipitate during the clarification phase of the must and subsequently of the wine.
The name lees offers no indication of the potential quality hidden in this sediment. Noble lees are often used in certain maturation processes, where the wine is deliberately kept on its lees to enhance nuance of aroma and flavour. Lees can be used in the distillation process in precise percentages.
These winemaking methods can be integrated and even summated so this description is only for information purposes. It helps to explain what pomace is by distancing it from the erstwhile idea of residual material from fermentation, putting it back in its rightful place as a raw material stemming directly from the grapes.
Grape pomace is a very delicate plant-based material which is prone to fairly rapid deterioration and therefore needs to be stored briefly after fermentation. If this is not the case, appropriate techniques need to be implemented to ensure proper storage.
In the past, pomace was often transported from wineries to distilleries without due care and potentially left in contact with air and in poor storage conditions for several days.
That era is now long gone and preserving the integrity of the base material is now considered to be the first important step in producing quality grappa.
If mishandled, uncontrolled fermentation of the pomace can occur as can the onset of bacteria, including acetic bacteria, which can compromise a successful product outcome.
Pomace can be sent to distilleries using various techniques. For example, it can be transported in large containers, tippers or closed bags. Generally speaking, the methods used guarantee optimal storage conditions, even during transportation, avoiding contact with air as much as possible.
Distilleries are equipped to receive the pomace, ferment it when required and then store it, possibly for short periods. Storage techniques involve aiming to remove air from the pomace, controlling acidity and even lowering it using the appropriate techniques, ensuring it remains at low temperatures. Air and oxygen are removed using compression and there are various methods for doing so. Innovation has greatly improved this aspect of production by providing compression systems that are less invasive than mechanical crushing. If the pomace is to be fermented, the choice of yeast is obviously also decisive so that aroma and flavour development can be maximised because they will be concentrated.
As mentioned above, distillation is the process which concentrates the desired substances and removes undesirable components from the distillate.
Distilling grape pomace to produce Grappa concentrates the low percentage of alcohol, ‘cleans’ this component that is not only alcoholic but also packed with a large range of compounds, and creates an end distillate that is perfectly transparent with all the requisite aromas and flavours.
If the pomace is handled badly, distillation will also concentrate the unpleasant components. No good Grappa can be made without excellent raw materials.
Silvia Castagner from the Castagner distillery located in the foothills of the Prosecco Conegliano Valdobbiadene area recounts: “We work closely with 250 local winegrowers for our supplies of excellent quality grape pomace. Every year, we painstakingly select the grape varieties best suited to the production of grappa and ensure the fruit is picked at peak ripeness. The main grape varieties selected include Glera, Pinot gris, Merlot, Cabernet, Muscat, Chardonnay and Sangiovese along with those used to craft our prized Amarone. We receive nearly 300,000 tonnes of grape pomace annually”.
“When we receive the pomace, we pay particular attention to its freshness and make sure it is in perfect health. We carefully monitor sugar levels and acidity, immediately discarding any low-quality pomace.”
“For the Glera and Pinot gris grape varieties, we separate the seeds from the pomace because the seeds contain a lot of polyphenols which are extremely sought after by the pharmaceutical and cosmetics industries. By separating the two, we can also produce a softer, rounder grappa with no bitterness at all”.
In terms of storage conditions, Silvia Castagner stresses: “White grape pomace is put through a fermentation process, whereas red grape pomace is stored in long plastic tunnels. The tunnels provide ideal conditions for preserving the integrity of our grape pomace, particularly our Amarone pomace whose exceptionally low humidity levels allow it to be stored for several months”.
The Bonollo Umberto distillery boasts eight collection centres for grape pomace which receive pomace from 5,000 wineries. Every year, they process no fewer than 150,000 tonnes of grape pomace. The amount is mind-boggling – it’s enough to fill two basketball courts, each eight metres high. That’s pretty impressive!
The distillery’s marketing manager, Valentina Ursic, comments: “The freshness of the grape pomace is essential. In order to preserve the quality of the pomace and avoid any undesired fermentation, the grape pomace is often delivered over night. And each load is put through stringent acidity tests – there can be no compromising on quality!”
Interestingly, whereas many Veneto distilleries have a penchant for the Glera variety – the darling grape of Prosecco – Bonollo sings from a different hymn sheet. It favours mostly pomace from Moscato, Recioto and of course Amarone – produced from Corvina, Corvinone and rondinella varieties -, the company’s flagship wine.
Steffano Bottega, the director of the Bottega distillery, also located in Veneto, comments: “We have the good fortune to work with around twenty suppliers, which enables us to process no fewer than 800,000 quintals of pomace (or 80,000 tonnes) every year. The pomace is received within 24 hours of harvesting and is immediately placed in silos to preserve its freshness”.
“We pay particular attention to the way the pomace is processed, based on its colour. Red pomace is dealt with very quickly whereas white pomace ferments for 25 to 40 days before being distilled”.
“To create our grappas, we mainly use white pomace from varieties such as Glera/Prosecco, Chardonnay, Sauvignon and Moscato, all of them sourced from the magnificent Euganean hills. For the red pomace, we select Cabernet and Merlot along with those of our own company stemming from Amarone”.
“Processing occurs in two different facilities. The first, our logistics centre, receives the precious pomace residue and produces an initial alcoholic liqueur. The liqueur is then transferred to our second facilities where it undergoes another distillation in order to hone our iconic grappas”.
Andrea Mazoni, master distiller at the Nardini distillery, explains: “Selecting suppliers is of paramount importance to us because we need high-quality pomace delivered within 24 hours. To guarantee freshness, we stock it and preserve it through silaging under plastic tarpaulins within twenty minutes of arrival. We insist on having experienced personnel for this process. The staff tasked with receiving the pomace has at least ten years’ experience and therefore the requisite skills for assessing the quality of the raw materials we receive. This is a fundamental procedure”.
He also stresses the changes being witnessed in the grapes, primarily due to climate change which has led to earlier harvests. Consequently, the proportion of white grapes used has increased compared with the past. The white grapes ferment for between 20 and 25 days before being distilled.
“When the pomace arrives at the distillery”, he adds, “an initial visual examination is conducted to eliminate any occurrence of mould, and samples are also sent to the laboratory for more in-depth analyses. These stringent checks have led to a considerable improvement in the quality of the grape pomace over the years. In the past, a lot of deliveries were rejected, mainly those from small producers who struggled to deliver their pomace quickly in good condition. Nowadays, things have changed a lot and the quality has come along in leaps and bounds”.
Andrea warns about the risks of mould or storage faults with the pomace, because they could ultimately end up in the distilled product. This is why care and attention paid to handling the pomace as soon as it arrives are essential for ensuring a high quality grappa.
Types of Distillation – Continuous-type stills
Only on the surface may the distillation of grape marc seem easy and the same for the theory that governs it, in practice things are much more complex and consequently the distillate is also affected in a more or less positive way by the variations that influence this operation.
There are many types of stills but they can be divided into two broad categories:
– continuous-type stills
– stills of the discontinuous type
The first case involves working with stills with good or excellent production potential, created to meet high production requirements at low operating cost. This principle does not necessarily place this type of equipment among the stills capable of producing low quality indeed in many cases these machines are capable of obtaining excellent products. Characteristic of the continuous still is that it does not have a loading phase a distillation phase and an unloading phase, but that it sums the three phases into one seamlessly.
It is difficult to categorise the types of still precisely because they can be built in a variety of ways and they can be operated differently depending on the production potential and the limitations on use of the pomace.
To summarise, a continuous-type still features:
- a system for extracting the alcohol and various substances from the grape pomace, producing an alcoholic vapour that condenses to form the ‘flemma’ or raw alcohol
- a system for accumulating the ‘flemma’
- one or more distillation columns with the capacity to strip the alcohol, i.e. concentrate the alcoholic percentage of the liquid, and remove the ‘flemma’, i.e. remove undesirable compounds from the alcoholic liquid.
Usually, continuous distillation columns are designed to distill liquids such as fermented cane juice, wines, grain wort. In the case of grappa, the alcohol contained in the solid pomace must first be extracted. The pomace is pushed first through long duct with steam pumped in the opposite direction to extract alcohol obtaining a liquid solution of approximately 25% ABV, named “flemma”. This alcohol solution is then sent to one or more conventional distillation columns for concentration and rectification to clean from unwanted compounds such as methanol.
These apparatuses can be of different sizes and performance, they can start from as little as 1,500 kilograms of distilled pomace per hour to as much as over 30,000 kilograms per hour.
Types of distillation – Discontinuous-type stills
There are many types of discontinuous stills used for grappa. Many distillers customise them and there are many commercially available solutions. Let’s have a look at the 3 most common stills.
Compared to continuous distillation, where there are no interruptions in the process, with discontinuous distillation – the clue is in the name – there is a loading phase, a processing phase and then an unloading phase.
This is why it is also referred to as batch distillation.
Special solutions have also been devised for distilling grappa, due to the fact that a solid substance is used and requires some care to prevent it from burning.
Discontinuous stills can be subdivided into:
- bain-marie discontinuous stills.
- discontinuous stills with cauldrons.
- direct fire stills.
The discontinuous bain-marie still
The discontinuous bain-marie still has three main parts: a distillation boiler, a column for stripping the alcohol and rectifying, a cooling system for the alcoholic vapours accompanied by a system for controlling the various distillation fractions.
In appearance, the bain-marie still looks simple to operate, but in practice it is not. To briefly summarise the way it works, it starts with the distillation boiler or cucurbit where the pomace immersed in water is loaded. Once loaded, the mass is heated by pushing pressurised water vapour into the cavity located next to and below the distillation boiler. In this way the skins are heated up with indirect heat source preserving the raw materials from being burnt. The purpose of the bain-marie is to mitigate the strength of the heat from the direct flame and prevent damage. The bain-marie distillation system is also widely used for distilling fruit.
The boiling mass of water and pomace develops alcohol vapours that are conveyed to the base of the distillation column and slowly pass through it, undergoing concentration and cleaning. Highly concentrated alcohol vapours exit near the top of the distillation column and are transported to the system now using various methods (tube bundles) – in the past only coils were used – where it comes out condensed towards the system that controls the head, heart and tail fractions. Basically, the first liquid exiting the condenser is considered to be the head fraction – it is unsuitable for consumption and is discarded until it reaches a certain alcohol content because it contains unpleasant and dangerous volatile compounds. That’s when the heart, i.e. the grappa, comes along. The third fraction, which is unable to reach a certain alcohol content, is also discarded and called the tail fraction. The tail fraction contains sulphur compounds and oily compounds.
The discontinuous bain-marie still is used to distil grape pomace as well as other types of fermented raw materials, including fermented pears or other types of fruit. In some cases, with appropriate modifications the bain-marie boiler can be used to distil fermented cereals and even molasses.
The discontinuous stills with cauldrons
To describe them simply, discontinuous stills with cauldrons basically have three parts: one or more distillation cauldrons, a column and a cooling system complemented by equipment for cutting the distillation fractions.
The distillation cauldron features a cylinder closed at the bottom and equipped with special valves for draining the liquid and injecting water vapour, and closed at the top with a large lid. Perforated partitions are placed inside the cauldron into which the pomace to be distilled is placed. The water vapour injected at the bottom of the cauldron passes through the grape pomace placed on the partitions and removes the alcohol and its component parts. This alcoholic vapour is conveyed through special piping to the distillation column where it undergoes concentration and alcohol stripping and is then bound for the cooling column to be condensed. In the discontinuous still with cauldrons, the head and tail fractions are also cut – only the heart fraction is kept. The cauldron system is widely used in many distilleries in the Veneto region.
The two discontinuous distillation systems have major differences in the way they operate. Also, the discontinuous cauldron still is more economical to operate than the more expensive bain-marie system, but it offers better and more gradual heating of the mass to be distilled.
Direct Fire Still
The direct fire still is the simplest and also the oldest version. Few distillation plants of this type are still in operation, the reason being that the system is very challenging to use because it can easily burn the pomace to be distilled. Controlling the heat must be carried out manually and with great care on the part of the operator, making it difficult to run this type of equipment, which is why it has been superseded by the more versatile discontinuous bain-marie system.
Excellent Grappas can be produced from each method and due to the countless variations on a theme chosen by the distiller or still manufacturer, there can also be hybrid solutions.
Is it possible to differentiate grappas according to the type of still used?
Usually the discontinuous ‘’bain-marie’’ distillation produces more delicate grappa, due to slower and gradual heating as well as a more precise ‘cutting of the heads’. But the differences between distillation methods are difficult to perceive and require a lot of experience.
Note: This blog post was originally written by Davide Terziotti and Thierry Heins, and published by Spirits Selection, who kindly allowed us to reproduce it on Inside the Cask.
0 Comments