Wine By-Products in Spain: Complete Guide on Grape Pomace, Wine Lees and Stems - Prices, Applications and Valorization

Spain maintains its position as a world reference in the wine sector, with a wine grape growing area exceeding 900,000 hectares, consolidating itself as the country with the largest vineyard area on the planet. This privileged position generates not only recognized quality wine, but also significant quantities of by-products derived from the winemaking process. With an annual wine production ranging between 35 and 40 million hectoliters depending on harvests, the Spanish sector generates approximately between 2 and 3 million tonnes annually of by-products, mainly grape pomace, wine lees and stems, whose proper management and valorization represents both an environmental challenge and an important economic opportunity.

The transformation of these by-products into valuable resources has evolved significantly in recent years, driven by the principles of circular economy and sustainability. From distillation to obtain alcohols and spirits to the extraction of high-value bioactive compounds such as polyphenols, tartaric acid and grape seed oil, the comprehensive use of wine by-products has become a strategic priority for wineries, cooperatives and valorization companies. This article analyzes in depth the characteristics, applications and market of the main wine by-products, providing updated information on prices, applicable regulations and business opportunities in this expanding sector.

Grape pomace: the main by-product of winemaking

Grape pomace constitutes the most abundant by-product of the wine industry, representing approximately 20% of the total weight of processed grapes. It consists of skins (grape peels), seeds and pulp residues remaining after pressing and must extraction. The approximate composition of fresh pomace indicates that it contains around 50% skins, 25% seeds and 25% residual pulp, with a dry matter content ranging between 30% and 45%.

There are significant differences between red and white pomace. Pomace from red winemaking has fermented together with the must, therefore it contains residual alcohol (typically between 5% and 12% by volume), presents higher tannin and polyphenol content extracted during maceration, and exhibits an intense reddish coloration. In contrast, pomace from white or rosé wine has not fermented with the must, has lower alcohol content, lower phenolic compound content and maintains a lighter color. This differentiation is fundamental both for its valorization and for determining its market price.

Pomace generation presents a marked seasonal character, concentrating mainly during the harvest period. Red wines, whose production is concentrated in the months of September and October, generate most of the pomace during this period. White wines, although also produced mainly in autumn, present a somewhat broader temporal distribution. This seasonality poses important logistical challenges for wineries and distilleries, which must manage significant volumes in short periods of time.

Wine lees: residues rich in yeasts and tartrates

Wine lees are sediments that settle at the bottom of tanks during and after alcoholic fermentation and, to a lesser extent, during wine aging. They are composed mainly of dead yeast cells, lactic bacteria, tartrates (tartaric acid salts), plant residues and organic matter. Although they represent a smaller volume than pomace, their chemical composition makes them a by-product of great interest to industry.

Two main types of lees are distinguished. Coarse or primary lees are generated immediately after alcoholic fermentation, contain a higher proportion of yeasts and solid residues, present higher residual alcohol content and constitute the most abundant type. Fine or secondary lees are produced during aging and wine racking, have lower solids content but higher tartrate concentration, present lower alcohol content and possess more refined organoleptic characteristics.

The residual alcohol content of lees typically varies between 3% and 8% by volume, being a determining factor in their valorization. The presence of tartrates, especially calcium tartrate, makes lees the main industrial source for obtaining natural tartaric acid, a product of high commercial value with multiple industrial applications.

Stems: the woody structure of the cluster

The stem, also called rachis or stalk, is the woody and structural part of the grape cluster that is separated during the destemming process, prior to fermentation. It represents approximately 4% of the total weight of processed grapes and is characterized by its high lignin, cellulose and hemicellulose content, which gives it properties similar to other lignocellulosic residues.

The composition of stems includes dry matter around 80-90%, vegetable fiber (lignin and cellulose) representing between 60% and 70% of its dry weight, moderate content of tannins and phenolic compounds, residual moisture of 10% to 20% depending on handling, and traces of alcohol if not separated before fermentation. Its generation coincides with the beginning of the harvest and varies according to the destemming system used by each winery.

Market prices and valuation factors

The market for wine by-products in Spain presents a complex structure where prices vary significantly according to multiple factors. For grape pomace, the price typically ranges between highly variable values, from situations where wineries must pay for its removal to cases where they receive economic compensation. Pomace with high alcohol content (8-12% vol) from quality reds can reach positive values of 10 to 30 euros per tonne in some wine regions. White wine pomace or pomace with low alcohol content generally has lower commercial value. In many cases, especially in large cooperatives in Castilla-La Mancha and Extremadura, contracts include free transfer of pomace in exchange for collection by the distillery.

Wine lees present a different price structure. Lees with high tartrate content are the most valued, reaching between 15 and 40 euros per tonne depending on their tartaric acid richness. Lees with high alcohol content have additional value for distillation. The lees market is more stable than that of pomace, with contracts frequently established with companies specialized in tartrate extraction. In prestigious designations of origin such as Rioja, Ribera del Duero or Rías Baixas, lees can reach higher prices due to their better quality.

Stems traditionally have the lowest commercial value of the three by-products. Their price as energy biomass varies between 5 and 15 euros per tonne in dry and crushed format. For composting, they are frequently transferred at no cost in exchange for their removal. Some advanced valorization initiatives are exploring their use for bioactive compound extraction, which could increase their future value.

The factors that determine these prices include geographical location and distance to valorization plants, as transport costs are significant for products with low added value and high moisture content. By-product quality, especially alcohol content in pomace and lees and tartrate richness in lees, is determining. Seasonality marks the market, with higher demand and better prices during harvest. The volume available per generator influences, with large volumes being more attractive as they allow economies of scale in logistics. Prior contracts between wineries and distilleries or valorization companies establish specific conditions that may differ from the spot market. Finally, public aid for by-product distillation, established within the CAP framework, indirectly influences the market by guaranteeing the viability of authorized distilleries.

Industrial applications and valorization pathways

Alcohol distillation traditionally represents the main application of pomace and lees in Spain. Authorized distilleries process these by-products to obtain wine alcohol with a minimum strength of 92% by volume, intended for industrial or energy use as bioethanol. Pomace brandy, a traditional spirit drink especially rooted in Galicia, is obtained by distilling fermented pomace in stills, reaching between 37.5% and 45% alcohol content. This process is regulated by European regulations and must meet strict specifications on maximum methanol content and presence of volatile substances.

Tartaric acid extraction from wine lees constitutes one of the highest added value applications. Natural tartaric acid is obtained through acidification, neutralization and crystallization processes of lees, especially fine lees rich in tartrates. This product finds applications in the wine industry as an acidity corrector for musts and wines, in the food industry as an acidulant, preservative and antioxidant, in the pharmaceutical industry as an excipient and in various chemical applications. The global tartaric acid market, where Spain is a relevant producer, especially values the natural origin product versus synthetic alternatives.

Bioactive compounds present in pomace have generated growing interest for their antioxidant properties and applications in various sectors. Polyphenols, especially resveratrol and anthocyanins present in red grape skins, are extracted for use in nutritional supplements, cosmetic products and functional foods. Grape seed oil, obtained by pressing or solvent extraction of seeds, contains high content of polyunsaturated fatty acids (mainly linoleic) and vitamin E, finding applications in food, cosmetics and soap making. Tannins extracted from pomace have uses in the leather industry, wine clarification and as natural colorants. Natural color extracts, especially enocyanin from red skins, are used in the food industry as an alternative to synthetic colorants.

Composting and agricultural use of pomace and stems represents a traditional and accessible valorization pathway. Compost made from these by-products, frequently mixed with other organic residues to balance the carbon/nitrogen ratio, provides an organic amendment rich in organic matter, although deficient in nitrogen, phosphorus and potassium. Its application improves soil structure, increases water retention capacity and provides micronutrients. However, it requires adequate composting to avoid phytotoxicity problems due to tannins and should be applied moderately due to its boron content.

Animal feeding with dealcoholized pomace has limited application. After distillation, exhausted pomace presents low nutritional value due to its high poorly digestible fiber content, high tannin concentration that reduces protein digestibility, and deficit of energy and digestible protein. It is mainly used as ballast feed in ruminants when forage prices are high, and represents only approximately 3% of total pomace production in Spain.

Use as energy biomass especially takes advantage of stems and dry pomace. With a calorific value of dry stems of approximately 16-18 MJ/kg and dealcoholized pomace of 14-16 MJ/kg, they can be used in biomass boilers, especially in wineries themselves for heating and hot water production, and in electricity generation plants through combustion or gasification. Limitations include high initial moisture content requiring drying, ash content and possible presence of chlorine that can cause corrosion in boilers.

Emerging applications include biogas production through anaerobic digestion of pomace and lees, taking advantage of their content in residual sugars and easily fermentable organic matter. Research into second-generation biofuels explores the conversion of the lignocellulosic fraction into advanced bioethanol. The development of bioplastics and biomaterials from cellulosic fractions is in the research phase. The extraction of specific compounds such as prebiotics (mannoproteins from yeasts present in lees) and other high-value products represents the future of bioeconomy applied to the wine sector.

Logistics and by-product management in wineries

Efficient management of wine by-products poses important logistical challenges for wineries. During harvest, the concentrated generation of large volumes of pomace in just a few weeks requires adequate temporary storage space, efficient collection and handling systems, and close coordination with distilleries and valorization companies. Pomace storage requires conditions that minimize alcohol losses through evaporation, avoid unwanted fermentations that can generate bad odors, and prevent mold development, all while maintaining temperatures below 30°C.

The most frequent commercialization models include annual contracts with distilleries that ensure regular by-product collection in exchange for a fixed price or free transfer, direct sale to valorization companies specialized in high-value compound extraction, management through second-tier cooperatives that group by-products from multiple wineries to improve negotiating power, and in some cases, own valorization when the winery has distillation or composting facilities. European and Spanish regulations require wineries to properly eliminate by-products before the end of the wine campaign, which conditions management strategies.

Regulatory framework and applicable regulation

The management of wine by-products in Spain is regulated by a complex regulatory framework that integrates European and national legislation. Regulation (EU) 2021/2115 of the European Parliament establishes the general framework of the Common Agricultural Policy, including specific measures for the wine sector. In Spain, Royal Decree 905/2022 regulates the Wine Sector Intervention within the framework of the CAP Strategic Plan, establishing aid for by-product distillation. Law 24/2003, on Vine and Wine, constitutes the national regulatory basis for the sector.

Pomace and lees are officially classified as winemaking by-products, not as waste, provided they are destined for authorized valorization. This distinction is fundamental from a legal and environmental point of view. Distilleries must be authorized by autonomous communities to be able to process these by-products and access public aid. The alcohol obtained must have a minimum strength of 92% by volume and be used exclusively for industrial or energy purposes, and cannot be used for direct human consumption.

Regulations on pomace brandy, regulated by Regulation (EC) No. 110/2008 and national legislation, establish strict technical specifications. The product must be obtained exclusively from fermented and distilled grape pomace, distillation must be carried out in the presence of pomace at less than 86% by volume, the content of volatile substances must be equal to or greater than 140 g/hl of alcohol at 100% vol, and the maximum methanol content is 1,000 g/hl of alcohol at 100% vol. These specifications guarantee the quality and safety of the final product.

Regarding animal feed, the use of wine by-products is subject to food and feed safety regulations. Pomace must be completely dealcoholized before use as feed, must comply with established contaminant limits, and requires registration of the establishment that processes it. Restrictions are due to the high tannin content that can negatively affect animal health and the possible presence of residues from vineyard phytosanitary treatments.

Traceability is a fundamental requirement throughout the process. Wineries must maintain detailed records of by-products generated, their destination and delivery documentation to authorized managers. Distilleries and valorization companies must record the reception, processing and final destination of products obtained. This documentation is supervised by competent authorities and verified in official controls.

Trends and circular economy models

The Spanish wine sector is experiencing a significant transformation in its approach to by-products. Numerous wineries of different sizes are implementing circular economy models that seek comprehensive use of all generated waste. Large cooperatives in regions such as La Rioja, Castilla y León or Navarra have developed or collaborate with integral valorization plants that process tens of thousands of tonnes annually of by-products, obtaining multiple marketable products: alcohol of different purities, tartrates, natural colorants, seed oil and residual biomass.

Innovation in high-value compound extraction is allowing specialized companies to develop increasingly efficient processes to obtain polyphenols, resveratrol and other antioxidants with applications in nutraceuticals and cosmetics. These initiatives, frequently supported by university research projects and technology centers, are raising the value of traditionally little-used by-products.

Integrated biorefinery projects represent the future of the sector. These concepts seek to implement cascade processes where each valorization stage takes advantage of specific components, maximizing overall economic performance. Collaboration between wineries and valorization companies is evolving towards more integrated models, with long-term agreements that guarantee regular supply of by-products and allow investments in advanced technology.

Conclusions and commercial opportunities

Wine by-products represent a resource of growing value within the framework of circular economy and environmental sustainability. The approximately 2 to 3 million tonnes annually of pomace, lees and stems generated in Spain constitute a raw material with multiple valorization pathways, from traditional applications such as distillation to innovative developments in the extraction of high-value bioactive compounds.

For wineries and cooperatives, efficient management of these by-products has ceased to be simply a regulatory obligation to become an opportunity for value generation and sustainability improvement. The correct selection of commercial partners for valorization, negotiation of fair conditions that reflect by-product quality, and exploration of innovative valorization pathways constitute strategic aspects of growing importance.

Companies specialized in valorization, especially those with technological capacity for advanced extraction processes, find expanding business opportunities in this sector. The development of high-value products such as polyphenolic extracts, superior quality tartaric acid or specialized oils responds to growing demands from demanding markets in sectors such as functional food, natural cosmetics and pharmacy.

The current context, marked by the transition towards more sustainable models and the revaluation of previously underutilized resources, favors the development of innovative initiatives in this field. The availability of public aid, the regulatory framework favorable to circular economy and the growing environmental awareness of the sector create a conducive environment for investments in valorization capacity and technological development.

In this context, specialized platforms such as Biomket facilitate efficient connection between wine by-product generators and companies interested in their valorization, optimizing commercialization especially during the intense harvest period. The professionalization of commercialization channels, together with continuous technological development in valorization methods, promises a future where wine by-products reach their full potential as valuable resources in the Spanish agri-food value chain.