1 The Australian Wine Research Institute, PO Box 197, Glen Osmond (Adelaide) SA 5064, Australia 2 Nomacorc SA, ZI Les Plénesses, Chemin de Xhénorie, 7,

4890 Thimister-Clermont, Belgium

Dissolved oxygen measurements during grape processing in the winery

Martin P. Day1, Olav Aagaard2 & Elizabeth J. Waters1

Introduction

. A lot is now known about dissolved oxygen (DO) in bottled wine but how much is introduced right at the beginning of the winemaking process?

. This talk is a summary of some of our observations on crushing and pressing => context of the complex phenomena happening.

Summary of talk

. Introduction . What happens when grapes are

crushed . Measurement methodology . Observations from crushing . Observations during

pressing – Normal mode

– Inert mode . DO values

after pressing . Conclusions

The factors for grape oxidation

What happens when grapes are crushed? • Caftaric acid:1,2diphenol (catechol) forms quinone radicals with PPO in oxygen • The sulfite ion protects the must by reducing the quinone back • p-Coutaric and other phenols can also form reactive radicals •

•

Flavonoids (esp. catechins) can also form radicals and

•

•

GRP = 3-S-gluathionyl caffeoyl tartrate

Measurements in the winery – Crushing Uni of Adelaide -WSL Josef Chromy Wines, TAS

DOOBSERVED = DOACTUAL –DOCONSUMED

Caveat utilitor!

Mean DO during crushing

¾ Hyperoxidation experiments → Must can absorb about 40 mg/L O2

Implications for improving crushing

. Inert the crusher ! . US patent 05/107176

granted June 1973 ! . Commercial equipment now

on market:

Measurements in the winery – Pressing

DO profile during pressing of crushed machine-harvested Riesling(Bucher Xpert 250: ORTAL program)

Effect of ‘splashing’ …and loose fittings

Inerted (N2) whole bunch pressing (Willmes Sigma)

Data from: Boselli, E et al. LWT 2010 DOI:10.1016/j.lwt.2010.03.006

Final DO values after pressing

. LOQ of PSt3 dot ca 20 ppb

. After only a few hours, the DO has dropped to around 20 ppb !

. What implication does this have for good fermentation kinetics?

Conclusions

. Clearly grapes are exposed to a substantial amount of oxygen as

soon as they are ruptured.

. A lot more work needs to carried out to understand how and

when critical oxygen exposure occurs. . Is protecting must from oxygen really what you want?

. Technology can help -modifications seem quite simple

Thanks

. AWRI: Maurizio Ugliano, Gemma West, Mark Braybrook

. Nomacorc: Mai Nygaard, Jean-Baptiste Dievel

. Josef Chromy Wines: Jeremy Dineen

This work was supported financially by Australia's grapegrowers and winemakers through their investment body the Grape and Wine Research and Development Corporation, with matching funds from the Australian Government, and by Pernod Ricard Pacific.

The AWRI is a member of the Wine Innovation Cluster located in Adelaide.

100% O2 -10 mL/min -60 µm sinter