Magnetic treatment could be used to remove off-flavours in wine

Scientists have used magnetic particles to isolate and reduce high levels of alkylmethoxypyrazines (MPs) – which can cause off-flavours – in Cabernet Sauvignon, without altering the overall aroma and flavour profile.

According to a study recently published in the Journal of Agricultural and Food Chemistry entitled in ‘Chemical and Sensory Evaluation of Magnetic Polymers as a Remedial Treatment for Elevated Concentrations of 3‑Isobutyl-2-methoxypyrazine in Cabernet Sauvignon Grape Must and Wine’ magnetic polymers can reduce off-flavours in Cabernet Sauvignon while preserving other volatile aromas and maintaining overall aroma intensity and fruity characters.

Conducted by David Jeffery along with a team at the University of Adelaide, the investigation examined whether attaching magnetic nanoparticles to polymers would allow one to isolate and reduce levels of MPs in wine.

Alkylmethoxypyrazines (MPs) are a group of grape compounds that impart vegetal and herbaceous notes in wines. IBMP (3‑Isobutyl-2-methoxypyrazine) is consistently found in higher quantities than the other two MPs and is often described as giving off a green bell pepper aroma. It forms part of the varietal characters of grapes such as Sauvignon Blanc and Cabernet Sauvignon and can be detected at 10ng/l and recognised at 15ng/l.

The level of MPs depends on grape ripening, with sunlight exposure and temperature during the ripening process playing a large part in IBMP concentration in the finished wines. This means that grapes harvested early and/or grown in cool climates often contain more IBMP. According to the study, the “usual winemaking process generally has little effect on final IBMP levels in wine”.

Scientists have already experimented with a number of different methods to try to reduce off-flavours in wine. Pre-fermentation maceration / heat treatment can eliminate up to 50% of IBMP but can introduce “cooked aromas to the finished wines”. Additives such as bentonite, oak chips, deodorised oak chips and activated charcoal, according to the study, have either “no effect” or “lack selectivity” and can remove desirable aromas and flavours.

In their experiment, scientists investigated pre and post-fermentation additions of a putative imprinted magnetic polymer (PIMP) in Cabernet Sauvignon must containing high levels of IBMP. They also compared the results when using a non-imprinted magnetic polymer (NIMP) and a polylactic acid (PLA) based film added post-fermentation – the latter is a commercially available treatment which has “been reported to remove MPs from wines with no or minimum effects on other volatile compounds according to gas chromatography-mass spectrometry (GC-MS) analysis”.

The results of the study found that PIMP treatments were more effective than PLA film for reducing “fresh green aroma nuances without negatively impacting overall aroma profiles”. The scientists also found that adding the magnetic polymer post-fermentation removed up to 74% of the initial IBMP, compared to an 18% reduction for PLA. However, it found that adding the PIMP pre-fermentation, although it removed 20-30% less IBMP, also had less of an effect on the other aromas and flavours.

In conclusion, the scientists noted: “Further research is still necessary to improve the imprinting process and enhance the selectivity of a magnetic polymer to arrive at an optimum dosage for a more specific remedial treatment under different wine matrix conditions. Furthermore, the format for magnetic separation of polymers would need to be investigated for an industry scale approach but would likely involve the use of magnetic filtering with an electromagnet, as used in the food industry”.

The full article can be read here.