we don't know what the concrete tanks are coated with...

A couple of relevant links:

Concrete fermenters: from old school to New World Wines & Vines ...Even wax- or steel-coated concrete tanks share that ... It gives you more integration into the wine ... it softens the wine and adds butter and toffee ...
findarticles.com/p/articles/mi_m3488/is_11_86/ai_n15932774 - 27k - Cached - Similar pages

Commonsense winemaking - Column Wines & Vines - Find ArticlesQ: We bottled wine in June and then had to leave two wood tanks empty until fall. ... This procedure will usually clean up wine tanks that have become ...
findarticles.com/p/articles/mi_m3488/is_n11_v74/ai_14629628 - 26k - Cached - Similar pages
[ More results from findarticles.com ]

Wine: An Introduction - Google Books Resultby Maynard A. Amerine, Vernon L. Singleton - 1977 - Cooking - 384 pages
It is difficult to have stainless steel, glass-lined, or coated concrete tanks just the right size for each lot of wine (Figure 13). ...
books.google.com/books?isbn=0520032020...


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Note added at 5 hrs (2007-12-06 17:16:59 GMT)
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Sorry! the middle link isn't relevant



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Note added at 5 days (2007-12-11 16:25:05 GMT) Post-grading
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thanks Deborah, any time! But I'm having misgivings about having the points, as I now see that Rocio proposed this same answer long before I did! Should you wish to reaward them to her (regrade the question), I give you my full permission. I find it so maddening when other people come up with "my" answer (or something very like it!) and get given the points...

Unless of course you found my answer more helpful for some other reason (explanation, refs...) in which case I accept more than graciously!!