## 1 Introduction  
3-alkyl-2-methoxypyrazines (MPs) are a group of substances detected in wines made from Sauvignon Blanc, Cabernet Sauvignon, Cabernet Franc, Merlot, Carmenere, Semillon, and other varieties [1]. Those compounds contribute to the 'green pepper' of wine aroma and have extremely low thresholds, ranging from 2 to 16 ng/L detected in wines [2]. With the increasing sensitivity of detection technology, seven MPs have been identified in grapes and wines [3]. Among them, 3-isopropyl-2-methoxypyrazine (IPMP), 3-sec-butyl-2-methoxypyrazine (SBMP), and 3-isobutyl-2-methoxypyrazine (IBMP) are the most abundant in grapes and wines, especially IBMP with undesirable herbaceous, green, and vegetal notes. IPMP has been reported only a few cases of its concentration exceeding the detection threshold and impacting wine flavor, while SBMP exhibits limited effects on wine quality [4].  
However, aroma characteristics of wines cannot be explained only from the knowledge of aroma composition alone. Interactions among various aromas play an important role in determining wine qualities. Although IBMP is considered to be responsible for 'green pepper' notes in wines [2; 5], in some recent research, poor correlation was obtained when concentration of MPs was compared with aromatic intensities of 'green pepper' attributes, because of the contribution of other aromatic compounds such as varietal thiols, C6 alcohols, and dimethyl sulfide, and the suppressive effect of the reductive aromas or aldehydes on fresh green attribute should not be underestimated [6; 7]. 'Green' aroma contributed by MPs was reported to be suppressed by the presence (or higher concentrations) of 4-ethylphenol, 4-ethyl guaiacol, and isopentanoic acid through CATA methodology analysis [8]. Previous studies also found the presence of volatile phenols may manifest 'green' characteristics such as 'herbaceous' and 'grassiness' even if IBMP levels are low [9; 10]. In addition to 'green pepper', IBMP could contribute to other attributes along with some aroma-active compounds in wines, as it was found positively associated with 'woody' and 'tobacco' flavor in wines [11]. Although IBMP could be considered appropriate for some wine varieties by adding aroma complexity, it is generally regarded as negative traits, as the presence of IBMP might also lead to the indirect suppression effect of 'clear/fruity' notes in both white and red wines [12]. The masking effect of IBMP on the 'tropical passionfruit' notes contributed by 3-mercaptoethanol-1-ol was investigated [13; 14]. Therefore, viticultural and enological treatments have long been trialed to remove MPs and to reduce MP-derived greenness [12].  
During winemaking, the blending technique after fermentation (_'coupage'_) is conducted through blending wines with different characteristics to increase wine quality, mainly by equilibrating the composition of wines, increasing stability and complexity, and modulating wine flavor with specific purpose [15]. However, although chemical components usually follow linear relationships as proportional change, aroma perception in blending wines is more complex to be regulated because of sensory interactions among volatile compounds [16]. The aim of this work is to investigate interactions between IBMP and other volatiles and provide scientific theory on wine blending technique. Sensory expression of IBMP was modified through a binary blending design of one dry red wine that contained high levels of MPs with three different monovarietal red wines. Combining analysis of different blending wines at three-month intervals during six-month bottle aging with the results of reconstituted aroma matrices, the effect of green pepper aroma on wines and the contribution of other aroma active compounds was investigated.