The Ratio of Increased Free-SO₂ to Total-SO₂ in the Various Wines Added with K-Metabisulfite

Studies on the Use of SO₂ in Wine Making (Part 16)

Abstract

In order to confirm the suitable amount of SO₂ necessary for storage of wine, the ratio of increased free-SO₂ to total-SO₂(F/T ratio) resulting from the added SO₂ in different wines were estimated after sulfiting and incubation for 3 days at 15°C.
The following results were obtained.
(1) In the case of young varietal wines to which 100 ppm of SO₂ was added, the F/T ratio in red wines (6 samples) and in white wines (6 samples) varied from 22.0 to 28.0% and 28.9 to 46.2% respectively. The F/T ratio increased about twice in the wines to which 200 ppm of SO₂ was added, compared to those with 100 ppm of S0₂.
(2) In the case of different vintage (1978-1984) wines, the F/T ratio in these wines depended on the added SO₂, and notably increased with higher level of SO₂ added.
By the addition of SO₂ 100 ppm, it was found that the F/T ratio were about 80% for white wines (Koshu) and about 70% for red wines (Muscat Bailey A).
(3) The concentration of three SO₂-acceptors, i. e. acetaldehyde, pyruvate and α-ketoglutarate, in wines differs with year of wine production. Equal amount of SO₂ was added to wine of each vintage and the amount of free and bound SO₂ was determined.
The results show that the F/T ratio did not differ significantly among wines of different vintage. It was suggested that the amount of free-SO₂ and bound-SO₂ in the wines had already been attained to a state of equilibrium.
(4) It was shown that the F/T ratio in many white wines (76 samples) and red wines (76 samples) of different origin were about 80% and 60-70% respectively.
(5) Among 160 wines examined, there were 8 wines in which the F/T ratio was exceptionally low, i. e., 0-41.7%. It was considered that these wines contained a higher amount of SO₂-acceptors, especially those of acetaldehyde.