In order to make wine, grapes must undergo alcoholic fermentation. In the case of red wine, the vessel used for fermentation, dependent upon winemaker preference, will also contain the skins, seeds and stems. During fermentation, yeast produce carbon dioxide, this carbon dioxide causes grape solids to rise creating what is referred to as a cap. The cap can present a number of risks, a combination of acetic bacteria, the warmth of fermentation and oxygen could easily convert a vat to vinegar. For this reason, winemakers must manage the cap. Cap management also forms part of the winemakers desired stylistic preference. Tannins, anthocyanins and flavour compounds, all essential to a wines character, are found in large quantities in grape skins and so varying methods of cap management will greatly alter a finished wine. Fail at cap management, and you may well have failed the wine.
Aroma, tannins and colour
Wine aroma is complex, multi-faceted and difficult to comprehensively map out. The exact chemistry is intricate and extensive; however, to avoid unnecessary confusion, we can in the most part attribute a wines aroma to alcohols, esters and volatile aroma compounds. Volatile aroma compounds are present in both the skin and the juice of a grape berry and vary in concentration dependent upon variety. It is is theorised that these compounds serve an evolutionary purpose in that they attract insects who in turn assist with pollination and birds and other animals who eat the berries and disperse the seeds. The broad range of varying concentrations amongst different varieties is evidence of adaptation depending upon environment and immediate competition.
Precursors to these compounds, such as carotenoids (a precursor to norisoprenoids) perform functional roles in the grape berry. Carotenoids help protect grape tissue from UV light, which may explain why concentration spikes with increased sunlight exposure.
In the grape berry itself the majority of these compounds are bound to sugars rendering them non-aromatic. During fermentation, and for the first few months of ageing, a host of chemical reactions take place, reverting these compounds to their aromatic form, and making them ‘available’ to form part of a wines aromatic identity.
Tannins come from five sources: grape skins, seeds, stems, oak, and additives. Skin tannins are large, as they tend to polymerise more than tannins from other sources. Tannins, in part, function as a grape’s sunscreen, the more light that reaches a grape’s surface, the more tannins the skins produce and the thicker the skins become. Unlike colour, which begins to seep into must as soon as a grape’s skin is ruptured, tannins, especially seed tannins, require alcohol for extraction, the rate of tannin extraction increases as alcohol concentration rises during fermentation.
Colour is one of the most important attributes of red wine, the principal sources of the colour in red wine comes from anthocyanins, or their further derivatives, which are extracted and/or formed during the vinification process. Anthocyanins protect plant tissues/organs against many abiotic and biotic stressors and function as both sunscreen and an antioxidant.
Concentration of tannins, volatile aroma compounds and anthocyanins differs not only by variety but also dependent on environmental factors such as sunlight hours, water and nutrient availability and canopy management.
Loosely speaking, maceration is the stage, or stages, in winemaking where the tannins, anthocyanins and flavour compounds are leached from the grape skins, seeds and stems into the must. Technically speaking maceration begins as soon as the skins are broken and exposed to some degree of heat. However, it is generally accepted that primary maceration begins simultaneously with fermentation period, it is at this stage that the cap forms. During fermentation, cap management can fundamentally shape a wines finished style. In this piece I will explore methods of cap management and how particular variables may influence associated decisions.
Before discussing intra-ferment techniques, we ought to first discuss cold soak. Amongst a number of other innovations, the famed Henri Jayer pioneered this technique. Cold soak takes place pre-fermentation, winemakers avoid spontaneous fermentation by maintaining a temperature typically between 5 and 10 oC for anywhere from 5 to 10 hours to 10 days.
It is thought that while grape skins are in contact with juice prior to alcohol formation, overall anthocyanin extraction is enhanced, as is the extraction of aroma and flavour compounds, whilst tannin extraction is kept at bay. This is thought to improve the overall quality of the wine produced, dependent of course upon desired style.
Recent studies have shown not only that cold soaking different red varieties (in this case Cabernet Sauvignon, Shiraz and Merlot) results in varying style but also that climate is a determining factor. Cold-soaked warm-climate fruit shows larger colour differences than cold-soaked cool-climate fruit, with the greatest colour differences occurring in Cabernet Sauvignon. Further work has also shown that wines undergoing cold soak are less fruity and more floral.
At Hirsch, cold soak is, albeit on a block by block basis, the norm. Jasmine Hirsch tells me she appreciates the gentle extraction which the 3-4 day period can offer. That being said, she has recently experimented with, after discussing the topic with an Alsatian winemaker, no cold soak, and found very little qualitative difference in the finished wine. Studies on Cabernet Sauvignon have reached similar conclusions.
Jasmine is conscious of the increased likelihood of microbial issues associated with cold soak, she has found that even with careful practise VA levels are higher in cold-soaked wines. ‘Every additional input requires energy‘ she explains, as we discuss the practicalities of cold soak. The process is resource intensive, the Hirsch winery is open to the elements and so the must receives gentle management throughout to avoid spoilage. Cooling is also energy intensive and with an increased focus on sustainability there may be a future trade off as to whether the process is viable.
In addition to obvious stylistic advantages, cold soak allows native yeast to establish themselves prior to fermentation. Furthermore, the extended period of ‘rest’ pre-fermentation can mean that winemakers are able to achieve more accurate sugar and nutrient content analysis.
There are logistical considerations to consider when working with cold soak, these include crusher settings and transportation of berries. Depending upon the temperature of the grapes, dry ice can be added in layers to avoid spontaneous fermentation.
Pumpovers and punchdowns
Pumping over, remontage in French, is the process of drawing off the must from the bottom of the fermentation vessel and pumping it over the cap, soaking it, extracting flavour, tannin and colour and oxygenating the must. Traditionally, pumpovers were considered harsher than punchdown, thought to introduce more oxygen and result in a more intense style. However, understanding has since improved and the nuances of cap management are now better understood. Many opting for gentle extraction do much more remontage than pigeage, with some producers in Burgundy excluding pigeage entirely. Whilst one may intrinsically influence the wine more profoundly, each varies dependent on individual approach.
Pumpover can be gentle or aggressive, results depend upon a range of variables such as fermentation vessel, grape variety, ripeness, stem inclusion and fermentation length and temperature. Juice can be sprinkled gently over the cap, slowly wetting it, or it can be shot at high pressure, breaking up the cap and redistributing the solids within it.
Punchdown, pigeage in French, is the process of breaking up the cap and submerging it in to the must, this is usually done between 1-3 times a day. The process can be either manual or mechanical. Manual punchdowns are labour intensive and involve winery staff using a pigeage plate or fork to disrupt and submerge the cap by hand. Mechanical punchdowns are less common, they require a similar plate, this time attached to a hydraulic arm.
‘We only ever punchdown manually’ explain Jasmine, she spends time working with her team, training them how to punchdown. This is important, a punchdown is not just a punchdown, results vary depending on how you perform the technique. For her, pumpovers are a great way to aid the yeast, particularly at the beginning (the open winery can make kicking things off a little difficult) but punchdown gives the extraction level she desires and one which works with their fruit.
Standard plate-on-pole punching tends to be a more aggressive extraction technique than pumpover, the plate is more likely (the fork less likely) to break, tear, and crush the skins, facilitating more extraction of flavour and colour. Traditionally punchdowns were done by foot, in some cases they still are, Mark Fincham of Domaine Tawse once told me over dinner that under a number of circumstances, he will often opt to incorporate punchdown by foot.
Modern pumpovers are often considered more gentle than punchdowns, only the juice is moved and no plate comes into contact with the grape skins. However, it is important not to be dogmatic in our assertions of particular techniques and concepts. It can be tempting to oversimplify the complexities of wine. Most winemakers adopt a varied and adaptive approach to cap management. This approach will most often incorporate numerous techniques at different times throughout the fermentation and vary dependent on a number of variables which change year on year.
Cap management is of the utmost importance, both practically and stylistically. There are a number of cap management methods available, each offering varied rates of extraction. Furthermore, each method will yield further variation depending on a range of variables including exposure to oxygen, grape variety, stem inclusion, ripeness at harvest, extraction frequency, fermentation temperature and total length of maceration.
If you’ve little to no experience in a winery, understanding the influence of these methods and variables may prove tricky. It may be helpful in some cases to imagine each in the context of making a cup of tea, which is in theory centred around extraction. The tea bag the cap, the water the must, and the cup the fermentation vessel. Let’s take a look at some of these considerations in a little more detail.
Stage of Fermentation
Varying levels of oxygen are required at different stages of fermentation. In order to multiply, yeast need a healthy amount of oxygen at the start of fermentation. ‘It’s almost impossible to overdo the amount of O2 a fermenting must receives‘ says Randall Graham. Pumpovers introduce more oxygen to the must than punchdown, they also result in a more balanced temperature and yeast distribution. Studies have shown that a great deal of work is required to balance temperature gradients. As fermentation progresses, alcohol levels rise, meaning extraction varies dependent on stage of ferment. Punchdowns tend to extract more tannins, particularly as alcohol levels rise, given that tannins are more soluble in alcohol. Considering the aforementioned, appropriate cap management technique depends upon the stage of ferment.
‘For Pinot Noir it’s pretty simple, mostly pumpovers until the grapes start fermenting‘ explains winemaker, Rajat Parr. Raj tells me that until grapes start fermenting he opts for pumpover, he then switches to punchdown until the must is dry, he then briefly returns to pumpovers. The preference overall is for gentle extraction. A similar approach is taken at Domaine Tollot-Beaut: ‘During the first 4 days we pump, and them some pigeage, usually twice a day’ says Jean-Paul.
Generally speaking, Pinot Noir is light in colour, low in tannin and fairly aromatic. Pumpover near the beginning of the fermentation can enhance fruit expression and flavour extraction, whereas a small number of punch downs toward the end of the fermentation can promote extraction of structural tannins. This kind of approach may result in a lighter, less concentrated and arguably more elegant wine. Punching down toward the end of fermentation also helps release sugar trapped in intact berries and may give the fermentation a natural temperature boost. At this stage, pumpovers which incorporate more oxygen to the must, may also inadvertently stress the yeast and cause stuck fermentation; ‘lots of O2 at the beginning and middle of ferment, progressively less at the end’ explains Randall.
Grape variety and climate
Some grape varieties have more tannin than others. Cabernet Sauvignon, Nebbiolo, Malbec, Syrah/Shiraz, and Sangiovese are consider tannic varieties. In contrast, wine made from grapes like Pinot Noir, Gamay and Grenache, which have much thinner skins, are considered much less tannic. While grape variety provides a good idea of tannin concentration, ripeness also matters as does vineyard management.
Cap management is about extraction of flavour, colour and tannin. Even where climate is constant, different grapes offer different characteristics. However, even the same grape can vary drastically in different climates. A good example is Syrah/Shiraz. It has a lot of tannin, but expresses itself differently, depending on climate and vintage.
Cap management decisions ought to take this in to account and be adjusted accordingly. A Rhone Syrah growing in a climate relatively cool compared compared to Barossa Shiraz may require a little more extraction whilst a Barossa Shiraz may require a little less with care taken over temperature as not to over-extract.
In the case of Syrah, punching down can be a poor choice because of the resulting bitterness. A combination of pumping over with délestage may be the best approach. Some winemakers also avoid punching down on thin-skinned varieties, doing so can lead to the production of a great amount of debris, clarification would then be challenging.
Ripeness at harvest
Ripeness at harvest is a key factor in deciding how to manage extraction. The riper the grapes at harvest, the softer and more fragile their skins and the more present and prominent the tannins. Skin tannins protect grapes from the sun, as such warmer vintages and climates yield a thicker skin with more tannin content. Conversely unripe grapes yield green characters and harsh, bitter undeveloped tannins.
In either scenario, punchdowns can be inappropriate. Punching down underripe grapes increases extraction and resulting wines can be aggressive and unapproachable. Punching down extremely ripe grapes often results in over-extraction of tannins and a muddy deposit of skin, which are brittle when ripe.
‘If the skins get thicker then we will do more pump overs’ explains Raj, who aims to make Pinot Noir which is devoid of harsh tannins, approachable and delicate. Similarly at Tollot-Beaut, in Beaune, the warmer Burgundian climate in recent years has meant thicker skins at harvest, as such the amount of pigeage at the estate has dropped from twice per day to once.
Stem inclusion can make grape solids less vulnerable to damage from cap submersion. On the other hand, they make both punchdown and pumpover more difficult, something which Jasmine Hirsch attests to. Early on in a fermentation, manipulating a cap with 100% whole cluster may require walking around on it to break up the berries, because the cap just won’t move.
Frequency and volume
Conventional wisdom is that high frequency (2 to 3 times per day) is good because it yields more colour and tannin. However, considerable tannin extraction may not be desirable. For example, Petite Sirah is a particularly pigmented and tannic grape. Deep color can be achieved with less frequent cap submersion and that, in turn, can limit the quantity and harshness of the tannins.
Some winemakers believe frequent cap submersion is also important for proper temperature control. Fermentation generates a lot of heat, that heat rises, and the solid cap is less impacted by a tank’s cooling jacket than is the liquid. Other winemakers are less concerned about heat.
Similarly, the effect of frequent submersion on tannins, flavour, and colour varies depending on grape variety, ripeness, and stage of fermentation. If the juice has leeched a majority of available extract during the first part of fermentation, there are diminishing returns for continuing frequent punchdowns or pumpovers. If tannin extraction during the final phase is mostly from seeds, a winemaker will want to consider whether that extraction is appropriate depending on the style of wine desired.
Fermentation vessel (open/closed and material/shape)
Fermentation vessels can be open or closed. Open-top fermenters allow for increased oxygen, which is advantageous for yeast health toward the start of a ferment. Open-top fermenters also allow winemakers easy access to the cap. Furthermore, heat generated during fermentation can more easily escape, thus open-top may help better manage fermentation temperatures.
Open-top fermentations are more practical for small volumes of wine as more care is needed in tracking and managing oxygen, which if too great may facilitate bacterial spoilage to enter the fermenting must. At Hirsch, Jasmine works with stainless steel open top fermenters ranging from 2 to 7 tonnes, blocks are fermented separately in relatively small lots and as such open-top works well. Whilst minimising carbon characteristics, the heat lost through the top helps avoid super-hot temperatures during ferment, something Hirsch wish to avoid.
When it comes to material and shape one ought to consider how much oxygen is desired or required, how will temperature inertia impact desired style and how practical is each vessel in managing temperature and the cap. Considering vessel shape, if the fermentation tank tapers toward the top, punchdown tends to be less violent than a straight-sided tank. The taper yields a cap of smaller diameter, meaning the juice is more easily displaced as the cap is submerged. Less force is necessary, and the grape solids aren’t disturbed as much.
Further cap management methods
Rack and return, délestage in French, is a two-step process in which fermenting red wine must is separated from the solids by racking and then returning to the fermentation vessel to re-soak the solids.
Racking the fermenting juice oxygenates, or aerates, the wine and softens astringent tannins through oxidation. During delestage, the cap falls to the bottom of the vat while the wine is allowed to drain completely. Once the wine is completely racked, a portion of the grape seeds is removed to avoid imparting the harsh tannins in seeds to the wine.
Following racking, grape solids are allowed to settle separately from the fermenting wine for one to two hours or more depending on the size of the fermenting vat. The fermenting wine is returned to the vat over the cap using a gentle, high-volume pump to completely soak the grape solids for maximum color and flavor extraction while minimizing extraction of harsh phenols.
At Hirsch, particular blocks which have a tendency to tasted a bit under extracted toward the end of fermentation, those which the team feel have more potential, will undergo delestage. ‘Although it can be an extreme technique, I happy with results’ explains Jasmine, noting the care which is taken when racking off, too much can obscure terroir and extract more fruit than desired.
Submerged cap, chapeau submergé in French, is a technique which was widely used in Europe during the 19th century. Opposed to, although not mutually exclusive, punching down or pumping over, the submerged method holds the cap under the surface of the must for a fixed period of time (often until dry) meaning it remains permanently in contact, but not disrupted, with the must.
The method offers practical advantages to winemakers. At Ridge, Paul Draper tells of Dave Bennion’s serendipitous discovery of the benefits of submerged cap. In ’59, Dave and his wife, Fran, due to vacation were unable to perform the regular daily punching down of the cap, to overcome this be built a wooden grid to hold the cap below the skins. He and Fran were away for two weeks, when they returned, the wine was dry. Submerged continues to serve Ridge well, throughout the 70’s the approach was used to control tannin extraction in both Cabernet and Zinfandel. These days submerged cap is used exclusively for slow, full extraction in less tannin Zinfandels.
The method has been shown to yield wines which are richer in tannins and colour when compared to the same wine subject to floating cap. It is hypothesised that this variation is due to to the greater importance of the enzymatic oxidation reactions in the cap, but especially to the more important precipitations of potassium bitartrate, enhanced by the higher extraction of potassium from the skins during fermentative maceration.
Rotary fermenters are horizontal, automated tanks that rotate on an axis to mix the cap and grape must during fermentation. The horizontal orientation allows for a greater area of contact between the pomace and the juice than in a vertical tank or vat. Rebecca Murphy of Wine Business Monthly compiled an excellent overview of the functionality, benefits and potential problems of rotary fermenters.
Although little published research exists, work in the Australian and New Zealand Wine Industry Journal did show that closed-tank and rotary fermenting musts resulted in higher levels of alcohol and wine colour density, as well as higher levels of total anthocyanins, with lower levels of volatile acidity. There are a range of benefits and potential issues with rotary fermenters, Rebecca covers them in detail, but to summarise; the main benefits are wine style, which tends to be a soft, accessible, early-drinking red wine needing little ageing, and the main potential issues are practicality, size and expense.
Thermovinification is a pre-fermentation process which involves heating whole or crushed grapes to promote rapid extraction of phenolic compounds, particularly colour in reds. From a sensory perspective, the greatest benefit may well be the reduction of ‘green’ attributes that are often difficult, if not impossible, to eradicate in the winery.
The obvious advantage is the rapid extraction of colour. However, there are disadvantages. Heat may kill native yeast populations. For winemakers that are proponents of native yeast fermentations, this can make hot pressing a non-option.
Furthermore, native pectinase, essential in the role of polysaccharides in mouthfeel and stability, can be thermally destroyed during the process. Therefore, supplemental pectinase may need to be added to must either prior or during fermentation to aide in proper clarification of wines downstream.
Theremovinification has been used for botrysised fruit to inactive the laccase enzyme associated with botrytis, enhance colour stability in reds, as well as improve the aromatics and flavours associated with the final wine. ‘There was quite a while where we didn’t have any botrytis … if we do we might use some heating at 40c at the end of fermentation, to kill the laccase enzyme’ explains Nathalie Tollot.
Pneumatage, or also simply known as ‘pulsair’, is a process in which the must via it being brought up and over the cap through the use of pulsing large burst of compressed air through a stainless steel mixing probe or fixed injection port probes near the bottom of fermentation vessel. The rising bubbles break up the cap into individual berries and the wine juice spills up and over the top.
Nick Goldschmidt, winemaker at Goldschmidt Vineyards, finds Pulsair to be particularly effective at the beginning of a fermentation as a way to break up the cap and circulate the juice. Once the wine is fermenting, he switches to traditional punch-downs, continued use of Pulsair may mix things too well, extracting unwanted tannins.
Pulsair redistributes heat rapidly, leading to faster extraction, especially in larger tanks. For large wineries trying to push fermentations, this could lead to better efficiencies, particularly in low-priced wine. Lance Cutler covers Pulsair in more detail with a number of winemakers and consultants in Wine Business Monthly.
Capping it off
Cap management decisions ought to be considered an amalgimation of both desired style and practical considerations dependent upon both technical and intuitive analysis of the must. These decisions are unlikely to be static and may evolve vintage on vintage as both the climate and winemakers preference shift. It is unhelpful to consider these decisions in isolation, instead they are influenced by a number of other variables and decisions both up and downstream and should be considered as a part of that wider system.