Tips and Tools for Rosé Winemaking
Wednesday, October 17, 2018
Rosé wines are lightly colored and generally made from juice that has had minimal contact time with dark skins. Although no legal definition for the color of rosé exists, it is generally accepted that the color may range from light salmon to copper, vibrant pink, or even a pale crimson. The color is determined by the grape variety as well as the length and temperature of maceration. Winemaking decisions made during this maceration period have an important impact on not just the color, but on the mouthfeel and aromas of the final wine. In general, grapes pressed directly with minimal skin contact will yield the lightest colored wines, with aromas leaning toward floral, citrus and stone fruits.
In the U.S., the majority of rosés are produced by holding the juice in contact with the skins, before or during fermentation, until the desired color is achieved or by saignée, the bleeding of a small percentage of juice from red must. The light juice that is bled off is then fermented as rosé. When undergoing longer pre-fermentation maceration, the use of the non-fermentative yeast Gaia, can help in preventing the development of off-characters from spoilage yeasts. The saignée method generally yields darker colored rosé and wines with more berry fruit aroma. Rosé can also be produced by blending a small amount of red wine with white. Most rosé from Champagne is traditionally made in this manner.
Rosés are made to be consumed young and fresh with bright fruit flavors and aromas and the balance of a crisp white wine. As such, during winemaking, they must be protected from oxidation. In order to protect these delicate aromas during fermentation, the judicious use of an oxygen-scavenging tannin such as FT Blanc Soft, a "white" gall nut tannin that will not darken rosé, will help prevent oxidation. One can also use the yeast derivative OptiMUM White which naturally contains high levels of the antioxidant glutathione and can help preserve and promote delicate aromas. Research from the Centre du Rosé in Provence has shown that glutathione is especially important in preserving thiols in varieties naturally rich in these aromas such as Cabernet Sauvignon.
Enzymes may be used during crush to speed up color extraction and the breakdown of pectin for a more complete release of the juice and aroma compounds bound in the grapes’ flesh. The enzymes should be gentle to avoid extraction of astringent and/or bitter phenolics. Recommended enzymes are Scottzyme Cinn Free or Color Pro, Lallzyme Cuvée Blanc, Rapidase Expression Aroma or Extra Press. Care should be taken when using enzymes on highly colored varieties, particularly if the weather has been hot and the color has started to bleed from the skin into the flesh of the grapes.
The yeast strain can have a major impact on the flavor profile. Strains with a proven track record for producing excellent rosés are M83 (500g), W15 Yeast , Rhone 4600 (500g), Cross Evolution Yeast and IOC Be Fruits Yeast. Aromatic white wine strains, such as Elixir (500g)and QA23 Yeast, can bring out terpenes and aromatic thiols if the grape varietal contains the precursors. VIN13 Yeast and NT116 Yeast are extremely strong fermenters, thiol converters, and ester producers. ICV Okay Yeast and Sensy (500g) produce delicate, aromatic rosés without danger of yeast-derived H2S or SO2.
To fulfill the aromatic potential of the fruit, the yeast have certain nutritional requirements. Rosés are quite often deficient in nitrogen and lipids (survival factors). Rehydrating the yeast with GoFerm Protect Evolution front-loads the yeast with survival factors, keeping the cell membrane’s integrity through the end of fermentation. The YAN (Yeast Available Nitrogen) needed for a healthy fermentation may range from 150 ppm to 250 ppm depending on the yeast strain chosen, the form of nitrogen (organic or inorganic) and possible stress factors. Stress factors may include potential alcohol, clarity and microbial competition. When correcting YAN for rosé, a complete nutrient derived from autolyzed yeast is preferable to DAP (diammonium phosphate). Organic nitrogen (amino acids) is preferable to inorganic nitrogen (ammonia). Fermaid O, a natural source of vitamins and minerals, contains only organic nitrogen, which is 4–5 times more efficient than ammonia nitrogen. Many of the amino acids in Fermaid O are also precursors to fruity aromatic compounds.
Yeast lipid metabolism is strongly affected by the temperature of fermentation, thus the temperature of fermentation will impact a wine’s aromatic potential. Ideally, the fermentation temperature should be between 60–68°F (16–20°C). Although it was traditionally thought that fermenting at lower temperatures increased the potential for esters, we now know that this is not the case. Our current understanding is that ester production is strongly linked with organic yeast nutrition. At slightly warmer fermentation temperatures between 60–68°F (16–20°C), there is more ester production. Although more of these esters will volatilize at the higher temperature, the end result will still be greater than if the fermentation temperature had been colder. Higher temperatures post-fermentation can result in the loss of delicate aromatics, as important varietal aromas like terpenes are preserved by holding wine at colder temperatures. Temperature management and control throughout the production process are key.
Although malic acid is a key contributor to freshness in rosé wine, malolactic fermentation can be used to lower the acidity of an unbalanced wine and make it more microbially stable. However, sequential inoculation can alter the flavors and aromas by causing the loss of bright red fruit characteristics due to diacetyl formation. This can be avoided by using VP41 Malolactic Bacteria, a low diacetyl producing bacteria strain, and by co-inoculating the yeast and bacteria. When co-inoculating, the initial SO2 addition should be kept below 30 ppm and the bacteria should be added 24 hours after the yeast. Any diacetyl produced by the bacteria is soon consumed by the active yeast, preserving the fresh fruit characters.
Stabilization is perhaps the trickiest part of rosé winemaking. Tartrate and protein stabilization are as important as in white winemaking. For tartrates, traditional chilling and tartrate precipitation may be used. In combination with chilling, Claristar (a mannoprotein) can be used to inhibit nucleation and growth of tartrate crystals. For protein stabilization, bentonite remains the only answer.
Color stabilization frequently causes the biggest problems. The color of rosés often turns orange or brown. First and foremost, dissolved oxygen must be controlled to prevent phenolic oxidation and browning. Flashgum R Liquid or Inogum (gum arabics) can then be added just before bottling. This will have a protective colloidal effect and help maintain the original bright color of the wine. If the wine shows browning before bottling, fining with Polycel (1kg)(PVPP) or Potassium Caseinate (casein) can possibly remove the oxidized phenolic compounds. Bench trials are necessary before either addition.