Summary 

Fruit (i.e., non-grape) wines have a long history in cold-climate regions. Unlike grapes, berries often need to be diluted with sugar water before fermentation to balance their intense flavor and acidity. Most berry wines are made with around 50% water, but exact ratios vary, and optimal ratios are unknown for most berries. This study explores how different levels of dilution affect the fermentation and final quality of wine made from haskap berries, a cold-hardy superfruit. 

Researchers tested four dilution levels and measured changes in alcohol content, acidity, color, and antioxidant levels. They found that while dilution reduces berry compounds, it can improve flavor balance and acidity, making the wine more similar to commercial grape wines. However, dilution also lowers yeast nutrients—especially Yeast Assimilable Nitrogen (YAN)—which can cause fermentation to stall. Haskap juice had only ~50 mg/L YAN, far below the 120–160 mg/L needed for successful fermentation, especially after dilution. 

Key Takeaways: 

  • Diluted berry wines need extra yeast nutrients to ferment properly. 
  • Less fruit can still make good wine, with stable acidity and appealing color and flavor. 
  • Using less fruit per bottle could help producers stretch their harvests and reduce costs. 

Introduction 

Haskap berries (Lonicera caerulea L.) are prized for their vivid color, tart flavor, and high antioxidant content—traits that make them ideal for value-added products like wine. However, their intense acidity and strong flavor pose challenges for winemaking. Like many berries, haskaps are often diluted with sugar water before fermentation to create a more balanced and palatable wine. 

Despite the popularity of this approach, the impact of dilution on fermentation success and final wine quality has not been thoroughly studied. This research aimed to fill that gap by testing different dilution ratios of haskap juice with water prior to fermentation. The goal was to understand how dilution affects fermentation speed, nutrient availability, and the chemical characteristics of the finished wine. 

A 1:1 ratio of haskap juice to sugar water—commonly used in berry wine production—served as the reference treatment, allowing comparisons across a range of dilution levels. 

This study used ‘Aurora’ haskap berries grown at the Western Agricultural Research Center of Montana State University in Corvallis, Montana. The plants were established in 2015 and irrigated two to three times per week using drip emitters, receiving about 50 liters of water weekly. By July 2022, the berries had ripened to a high sugar content (above 17.5°Brix) and were mechanically harvested, yielding an average of 3.5 kilograms of fruit per plant. 

After harvest, the berries were cooled in a walk-in cooler and cleaned using a custom ramp and leaf blower setup that removed leaves, sticks, and other debris. The cleaned berries were then frozen at −20°C to preserve their quality until processing. Three days before pressing, approximately 25 kilograms of frozen berries were moved to a walk-in cooler set at 4°C with high humidity to thaw gradually. 

Once thawed, the berries were pressed using a 6-liter hydraulic fruit press, applying pressure gradually until reaching 3 Bar. This process yielded about 12.25 liters of juice, which served as the base material for fermentation experiments. 
 
Haskap juice was prepared at four dilution levels: 1:1, 1:2, 1:4, and 1:5 (juice to water). The final volume for each dilution was 3L and target SSC was 20°Brix (adjusted with corn sugar).  Adding sugar increases the volume so the % juice to total must/wine volume is slightly less than what would be calculated from these ratios. Each mixture was inoculated with commercial wine yeast and fermented in sanitized glass containers at room temperature. After fermentation, the wines were analyzed for several key parameters: 

  • Fermentation completion: Whether the yeast fully converted sugars to alcohol. 
  • Alcohol content: A measure of fermentation efficiency. 
  • pH and titratable acidity: Indicators of wine stability and flavor. 
  • Color changes: Reflecting pigment retention or degradation. 
  • Antioxidant activity: A measure of health-promoting compounds. 
  • Phenolic composition: Including anthocyanins, flavonols, and hydroxycinnamates. 

This design allowed the researchers to compare how dilution influences both the technical and sensory aspects of haskap wine. 

Yeast Needs More Than Sugar 
Fruit wines made from berries like haskap often require dilution with sugar water to balance their intense flavor and acidity. However, this dilution also reduces essential nutrients for fermentation—especially Yeast Assimilable Nitrogen (YAN), which yeast needs to thrive. While grapes naturally contain enough YAN (100–150 mg/L), haskap juice had only ~50 mg/L, and dilution lowered it further. Wines made from the most diluted juice failed to finish fermentation without additional yeast nutrients, highlighting the need to adjust nutrient levels when working with non-grape fruits. 

Dilution Can Improve Balance 
All wines in the study had stable pH (3.2–3.4) and good lab-measured flavor and color. Dilution reduced berry compounds, but also lowered acidity to levels typical of commercial grape wines (<10 g/L), making the wine more palatable. Adding small amounts of sugar during bottling can further balance acidity. 

Fermentation Success Depends on Dilution Ratio 
Wines made from less diluted juice (1:1 and 1:2 ratios) fermented successfully with standard yeast nutrition. More diluted wines stalled due to low YAN, reinforcing the importance of nutrient management in fruit wine production. 

Chemical Changes Affect Style and Appeal 
Wines from the 1:1 dilution had lower alcohol and pH but higher glycerol, which adds body and sweetness—potentially desirable depending on wine style. More diluted wines showed greater color changes, likely due to anthocyanin breakdown during fermentation. While antioxidant activity decreased in all wines, other phenolic compounds like flavonols remained stable. 

Bottom Line: 
Dilution can help balance flavor and acidity in berry wines, but it also reduces nutrients and beneficial compounds. Winemakers can optimize fermentation and wine quality by adjusting yeast nutrition and choosing dilution ratios that match their production goals. 

Conclusions 

Diluting haskap juice before fermentation offers a practical strategy for improving fermentation reliability and customizing wine characteristics such as alcohol content, acidity, and mouthfeel. Higher dilution levels can help ensure complete fermentation and allow producers to craft wines suited to different styles, including lighter or lower-alcohol options. 

However, this approach comes with trade-offs. Naturally, dilution significantly reduced several health-promoting compounds—especially anthocyanins, the pigments responsible for haskap’s deep color and antioxidant properties. While some loss is expected during fermentation, anthocyanin stability is also influenced by factors like pH, temperature, oxygen exposure, and additives such as sulfites or ascorbic acid. 

To preserve these valuable compounds and extend shelf life, future research could explore techniques like adjusting acidity or modifying sugar structures to stabilize anthocyanins. Fine-tuning processing conditions may help retain more of the fruit’s nutritional and visual appeal. 

In summary, juice dilution is a useful tool for managing fermentation and tailoring wine profiles. But to produce vibrant, high-quality haskap wines with strong health appeal, winemakers must also pay close attention to anthocyanin chemistry and overall fruit integrity.

Funding Acknowledgement 

This research is funded by the Specialty Crop Block Grant Program of the Montana Department of Agriculture, Grant No. AM22SCBPMT1127.