In Asia Pacific, China saw continued momentum across categories driven by both volume and improved mix with Trademark Coca-Cola.
Great Britain and Russia, where mobility was at the highest, show notable volume outperformance relative to 2019 and sparkling soft drinks gained or maintained share in most of the top 10 markets in Europe.
BIG also made great progress against its growth and productivity agenda, increasing year-to-date comparable operating margin, approximately 300 basis points from the 2019 levels.
For a few examples.
The Coke trademark portfolio is experiencing robust growth, led by brand Coke and driven in part by Coca-Cola Zero Sugar, which has contributed double-digit growth in value and volume year to date.
The new Coca-Cola Zero Sugar recipe has already launched in nearly 50 markets across six of our operating units, including last week's announcement in the U.S. with more to come this year.
Topo Chico Hard Seltzer is now in 17 markets worldwide, and we've authorized Molson Coors the right to produce and sell Topo Chico Hard Seltzer in the United States.
Highlights include the continued rollout of a 100% recycled PET with 30 markets representing approximately 30% of our total sales offering at least one brand in a 100% rPET packaging.
We've continued the expansion of refillables and dispense packaging and ultra-lightweighting technologies, and we delivered a 60% global collection rate for packaging in 2020.
Recently, we announced that we've become a global implementation partner for The Ocean Cleanup's river project, supporting the deployment of cleanup systems across 15 rivers across the world.
Our Q2 organic revenue was up 37%, comprised of concentrate shipments up 26% and price mix improvement of 11% as we lapped the biggest pandemic impacts of 2020.
Unit case growth was 18%.
As a result, second quarter comparable earnings per share of $0.68 was an increase of 61% year over year.
We also delivered strong year-to-date free cash flow of approximately $5 billion, double last year's results.
We now expect to deliver year-over-year organic revenue growth of 12% to 14% and comparable earnings per share growth of 13% to 15% in 2021.
Our steady focus on cash generation continues to yield progress, and our updated guidance for free cash flow of at least $9 billion implies a dividend payout ratio significantly improved from where we began the year and is edging closer to our targeted level of 75% over the long term.
Our currency outlook continues to contemplate a tailwind of 1% to 2% to the top line and approximately 2% to 3% to comparable earnings per share in 2021 based on current spot rates and our hedge positions.
We will also have some additional timing considerations with the leveling out of our concentrate shipments that are running a bit ahead year to date as well as six fewer days in the fourth quarter.

Summary:
In Asia Pacific, China saw continued momentum across categories driven by both volume and improved mix with Trademark Coca-Cola.
For a few examples.
The Coke trademark portfolio is experiencing robust growth, led by brand Coke and driven in part by Coca-Cola Zero Sugar, which has contributed double-digit growth in value and volume year to date.
Our Q2 organic revenue was up 37%, comprised of concentrate shipments up 26% and price mix improvement of 11% as we lapped the biggest pandemic impacts of 2020.
Unit case growth was 18%.
As a result, second quarter comparable earnings per share of $0.68 was an increase of 61% year over year.
We now expect to deliver year-over-year organic revenue growth of 12% to 14% and comparable earnings per share growth of 13% to 15% in 2021.
Our currency outlook continues to contemplate a tailwind of 1% to 2% to the top line and approximately 2% to 3% to comparable earnings per share in 2021 based on current spot rates and our hedge positions.
We will also have some additional timing considerations with the leveling out of our concentrate shipments that are running a bit ahead year to date as well as six fewer days in the fourth quarter.