The one certainty is that no deal will be struck unless it includes beef.
The key sticking point concerns "sensitive" agricultural products beef and ethanol. In relation to beef, there are additional unresolved food safety, animal welfare and environmental concerns, particularly in relation to Brazil.
At the heart of the divisions within the EU is the current offer to the four Mercosur nations of an additional 70,000-tonne preferential market access quota, involving a tariff rate of 7.5pc.
This includes 35,000t of fresh beef, made up of high-value Hilton beef and young grazing beef, plus 35,000t of frozen beef. A six-year transitional period is proposed.
This 70,000t is the first formal offer to Mercosur by the EU since negotiations restarted after a decade-long freeze.
A 2016 proposal of 78,000t was withdrawn before being formally offered due huge outcry across several member states.
However, while opposition to the deal in Europe centres on the quota offered being too big, Brazil's chief negotiator Ronaldo Costa Filho has also criticised it, for being too small.
According to Argentina's powerful farm lobby, the beef quota as proposed is equivalent to just two hamburgers a year per EU resident.
But, given that each carcass yields only about 12pc in prime cuts, the EU offer could entail total slaughterings of up to 600,000t, which is greater than Ireland's entire annual beef exports of 535,000t.
Joe Burke, beef and livestock sector manager with Bord Bia, said they would be "hugely concerned" about the impact of the proposed Mercosur offer.
"In a European market of 7mt beef, 70,000 might not seem that significant but it could have a major impact in terms of competition for our high-quality cuts going to Continental Europe," he said.
"It's an additional negative force within the EU, in light of Brexit and the growing numbers of cattle available for processing in Ireland."
A report last year by the EU Commission's own Joint Research Centre showed that upcoming trade agreements, led by Mercosur, could slash European beef prices by up to 16pc. The cumulative cost across the European beef sector could rise to €5bn annually, by 2025.
Because of Ireland's heavy dependence on exports, the IFA fears that the impact would be proportionally higher, potentially costing the sector €500-€750m.
Cattle represent 8.1pc of total EU agricultural output and 18.8pc of its animal output (excluding milk). In 2016, the EU imported a total of 333,957t beef carcase weight equivalent, three-quarters of this (246,743t) from Mercosur countries.
The majority of these imports are covered by what are called Tariff Rate Quotas, agreed under various rounds of GATT. These comprise a GATT frozen beef quota, A+B processing quota, Hilton quota and High Quality Beef (HQB).
This is a complex area, and the amount of tariff paid varies between the various quotas and the form in which the meat is sold, ie whether fresh or frozen.
For example, the High Quality Beef Quota (or HBQ), which has a zero-tariff rate, applies to high-quality fresh, chilled and frozen grain-fed beef that meets specific feeding and grading requirements. Of the Mercosur members, it is open to Argentina and Paraguay.
The Hilton quota, so named after the hotel in Tokyo in which the deal was struck during the 1979 round of GATT, applies a 20pc tariff rate on fresh, grass-fed beef, mainly steaks.
The quotas for high-value cuts in particular are used up quickly, indicating that additional quotas would be readily taken up, and higher-tariff meat would instantly be supplanted by lower-tariff product.
MEP Mairéad McGuinness has warned that anything which damages the market and reduces prices to beef farmers will be hugely detrimental not just to producers but also to the regions where beef production is an important sector, namely Ireland and France.
Agriculture and Rural Development Commissioner Phil Hogan has said: "Mercosur will have to moderate its demands to achieve a breakthrough. There will always be sensitive products in the EU that will have to be protected, and chief among those are beef and ethanol."
Trade minister Pat Breen said the latest Mercosur offer sets a "dangerous precedent" and marks a "sea change" in the Commission's approach to trade negotiations.
"Don't get us wrong, we think Mercosur will be a very good trade deal for everybody, there's some good stuff in it," Mr Breen told the Irish Independent after a meeting of EU trade ministers recently. "But you don't start off with a figure that high and put your cards on the table at this early stage."
Mr Breen conceded that it would be "unrealistic" to think Ireland could get beef off the menu entirely, but said he would continue to push back against the 70,000t offer - which, it has been rumoured, could even rise substantially during a November round of talks with Mercosur.
"We have to look at the figure that's involved here - we think the figure is substantial, they think it's too low, so it's a matter of compromise."
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