## 3 Effect of Cryogenic Technologies on Physicochemical and Aroma Compounds of Grape Must and Wine
### Effect of Cryogenic Technologies on Methoxypyrazines  
Methoxypyrazines (MPs) are volatile nitrogen-containing heterocyclic compounds found in plants, insects, fungi, and bacteria [74; 75]. They are primarily responsible for the vegetative, grassy, green pepper, capsaicin, and asparagus aromas present in Sauvignon blanc [6; 28; 75; 76]. The perception of green attributes is seen as positive and adds complexity to Sauvignon blanc [28; 76; 77]. The most essential MP found in grapes and wines is 2-methoxy-3-_iso_butylpyrazine (ibMP), the main contributor to the vegetative, grassy, green pepper, capsaicin, and asparagus aromas in Sauvignon blanc [28; 74; 75; 76]. It is typically present in wine as free volatile compounds in concentrations ranging from 2 to 30 ng L\({}^{-1}\) (Table 4).  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Cultivar** & **Compound \& **Aroma** & **Aroma** & **Range in** & **Range in** \\  & **Chemical** & **Description** & **Perception** & **Wine** & **SA 1 Wine** \\  & **Structure** & & **in Wine** & **(ng L\({}^{-1}\))** & **(ng L\({}^{-1}\))** \\ \hline
**Sauvignon blanc** & 4–methyl–4-sulfanylpentan–2–one (4 MSP) & Boxwood, blackcurrant & & 0–88 & 0–21.9 \\ \cline{2-6}
**Chenin blanc** & & & & & \\  & & & 0.8 & & \\  & & & & 0–23 & n.d. * \\  & & & & & \\  & & & & & \\ \hline
**Sauvignon blanc** & 3–sulfanylhexal acetate & Passionfruit, tropical, boxwood & & 0–106 & 23–151 \\ \cline{2-6}
**Chenin blanc** & & & & & \\  & & & 4 & & \\  & & & & 0–100 & 5–253 \\ \hline
**Sauvignon blanc** & 3–sulfanylhexan–1–ol (3 SH) & Graprefruit, tropical, passionfruit & & 350–5664 & 178–904 \\ \cline{2-6}
**Chenin blanc** & & & & & \\  & & & & & \\  & & & & 10–1368 & 99–1124 \\ \cline{2-6}
**Sauvignon blanc** & benzyl mercaptan (BM) & Smoke, toasty, struck flint & & 0.6–5.5 & n.d. * \\ \cline{2-6}
**Chenin Blanc** & & & & & \\  & & & & 30–40 & n.d. * \\ \cline{2-6}
**Sauvignon blanc** & 2–furfurylthiol (FFT) & Roasted Coffee & & 1–36 & n.d. * \\ \cline{2-6}
**Chenin blanc** & & & & & \\  & & & & & \\  & & & & & \\  & & & & & \\ \hline \end{tabular} \({}^{1}\) South Africa * Not detected; adapted from [53; 77; 53].  
\end{table}
Table 3: Varietal thiols present in Sauvignon blanc and Chenin blanc wines: aroma description, perception, and range in wine.  
Moreover, two additional MPs present in must and wine at lower concentrations are 2-methoxy-3-_is_opropylpyrazine (ipMP) and 2-methoxy-3-_sec_-butylpyrazine (sbMP), which contribute to the earthly, asparagus aromas [28; 74; 75]. Sensory detection thresholds for ibMP, ipMP, and sbMP are typically very low, i.e., 1-2 ng L\({}^{-1}\) in water and 2-16 ng L\({}^{-1}\) in wine [28; 74; 75]. Interestingly, during literature searches, the authors noted no publications investigating the effect of cryogenic treatments on MPs, which warrants further investigation and understanding as MPs are major contributors to the aroma profile of Sauvignon blanc wines. Previous research incorporating cryogenic practices focused mainly on their effect on major aroma compounds, i.e., polyphenols, terpen, esters, higher alcohols, fatty acids, as well as the varietal thiols, i.e., 3-SH, 3-SHA, and 4-MSP [28; 77; 31; 59; 78].