When the blog “The Wine-o-scope” posted this post, “The value of cold soaks for red winemaking” last week I was intrigued. Having done extensive phenolic analysis for several years with a few different red varieties, I always like to see what other people are finding. When I say extensive, I mean extensive. At my previous job, we would run phenolic analysis by Adams-Harbertson assay every day for EVERY high end red during fermentation. This was mainly Cabernet Sauvignon but also included Merlot and Cabernet Franc. We also looked at Pinot Noir just for the fun of it but we determined that the rules that govern phenolic extraction in Bordeaux varieties just don’t apply to Pinot Noir and left that sleeping dog lie. The timing of anthocyanin and tannin extraction still applies in Pinot Noir but I’ve found through my experience that the best analysis of Pinot Noir is still tasting it frequently.
Here is the reality of things based on real world, non research based experience. In Bordeaux varieties a cold soak absolutely increases color extraction, particularly with extensive cap management, vs tanks with little to no cold soak. It does not increase tannin extraction because tannins don’t really start coming into the solution of the wine until a reasonable amount of alcohol has built up.
You can see that at the point fermentation has started there is already close to 400 ppm of Anthocyanins extracted in the fermentation. This is after a 6 day cold soak with significant cap management. You’ll also notice that it is not until day 4 of fermentation (around 15 Brix) that we are able to detect any tannin extraction. This could be ANY Bordeaux variety fermentation. They all follow the same pattern. Just for fun, here is a Merlot graph from the same vintage, same vineyard, and same general area of the vineyard with fermentation starting within a day of the Cab above.
Aside from noticeably less anthocyanin and tannin content at dryness (because it is Merlot after all) the pattern of extraction is pretty much the same. Cab Franc is the same pattern as well.
Once one looks at enough of these numbers daily one doesn’t really even need the graph anymore. You just know what’s going on.
As far as the dangers of cold soak go, yes you do see an increase in other organisms and yes, you do occasionally get the random “wild” fermentation if you push the cold soak over 5 days. Also, if the fruit is not clean coming in the risk increases so sorting is essential to a clean and healthy cold soak. Dry Ice is your friend at this point and should be used liberally.
To me the true value of the cold soak is the period you are guaranteed to be extracting color without extracting tannin. Can you extract the same amount of color without a cold soak? Of course, but be prepared to have much higher tannin levels at dryness as well since you will be working the cap harder during the time of fermentation when both are extractable.
That’s just my opinion and again, this was not in a research but in real winery experience with no controls. Take it for what it is worth.