Are pH corrections necessary when making icewine?

As any winemaker knows, the riper your grapes get, the higher the pH climbs. There are schools of thought that even say that you should pick your grapes not based on Brix (and I would generally concur with this part alone), but on pH; another school of thought - the one I tend to practice - says to gauge ripeness by assessing the flavour of the grapes.

Having said all that, what sort of pH does one typically look at in grapes that have been left to hang for icewine? Just considering the super-ripeness of such grapes, it would seem that before botrytis and the requisite hard freeze do their work, the pH should be dangerously high. I'm assuming that loss of water content in the juice due to dessication via botrytis and then further concentration via freezing (water crystals migrating out of the juice) could, however, result in a re-concentrating of the acidity, thereby lowering pH.

But - is it quite so simple? Do pH adjustments still have to be made prior to fermentation, as a rule?

I think it depends on the grape variety. Generally, late ripening grapes with tough skins are used for icewine. Vidal ripens later than most, about the same time as Cab Franc, and later than Riesling. Since they ripen late, they tend to have enough high acid levels, even when left on the vine until it gets cold enough for icewine. As soon as there's a frost, the leaves fall off and further ripening is stopped. I don't think botrytis is really an issue, as most growers spray to avoid it as it is not something to be desired, unless one is attempting to make a botryticized dessert wine, which is not the same as icewine. In fact, I've never heard of a botryticized Vidal - I think it's immune. Vignoles, on the other hand has been made botryticized, but I've never heard of a Vignoles ice wine. As far as I know, Riesling is the only grape that could be made either way or both ways. Other grapes that I've heard of (or tasted) that are botryticized are Semillion & S.B. (Sauternes), and Pinot Blanc (Rulander in Germany). So, to answer your question, I don't believe raising the acidity level in icewine would be necessary in most cases.

Hi Paul,
There are those who use the UC Davis recommendation Brix to TA ratio (30 to 1 or 35 to 1) or Cox’s equation (the first time I say this equation was in his book “From Vines to Wines”) Brix times pH squared. He does note however to keep a watchful on TA and pH when trying to obtain desirable numbers (200 for white grapes and 260 for red grapes).
Even though I never attempted to produce an “ice wine”, I’m pretty sure there are “targeted numbers” or “desired numbers” to look for prior to fermentation.

Salute

I've been curious about this as well. The eisweins I've (German only, so far) have been very high in acidity. I've wondered how the acidity can be so high in a late harvest wine.

I've been curious about this as well. The eisweins I've (German only, so far) have been very high in acidity. I've wondered how the acidity can be so high in a late harvest wine.

Mike,
When you take water from the grape or juice, via a freezer or by nature, the acidity in that grape (or ml of juice) does not change...so many gm/ml (as tartaric). So as you reduce the water the per ml goes down, driving up the (specific) acidity. There's just now more acid there per unit volume. Not sure, though, what the pH does. It must go down as well.
Tom

As any winemaker knows, the riper your grapes get, the higher the pH climbs. There are schools of thought that even say that you should pick your grapes not based on Brix (and I would generally concur with this part alone), but on pH; another school of thought - the one I tend to practice - says to gauge ripeness by assessing the flavour of the grapes.

Ideally, "ripeness" would be assessed based on all information available (Brix, TA, pH, phenolics, flavour, physical attributes etc). However, some climates can almost garantee that one or more of the parameters are consistently met year after year with particular varieties and growing conditions etc. So some winemakers/growers pay less attention to those attributes in determining ripeness, and focus on the more variable ones instead - it just makes life simpler. (It's only possible/sensible when you know the fruit/conditions though.) I think the different "schools" come about because of this - one school of thought isn't necessarily applicable in another place/with another variety/with another style. I find it a bit ridiculous when people from different schools argue over the model to use (e.g., whether you should/shouldn't bother with TA) - in one place it will be so variable from year to year, and important for the style, that you need to watch it; but in other places not so. Which model you use is dependent on all these factors. That's my take on it anyway.

what sort of pH does one typically look at in grapes that have been left to hang for icewine? ...it would seem that before botrytis... Do pH adjustments still have to be made prior to fermentation, as a rule?

I don't think a blanket statement can be made in answer to those Qs. Firstly, it just depends on the variety and the climate etc. Secondly, icewine isn't necessarily Botrytised wine. With Bot you can expect a +0.2 unit shift in pH, though as you (and others) have pointed out removal of water may shift that in an icewine. Some musts/wines do show higher pH as you suspect (e.g., Vidal is often seen at >3.4 and are not adjusted). I guess it depends on your aims and what you're comfortable with. (After all, a pH of 3.7 can be OK in a dry red, it just means certain things. Likewise for icewine.)

Ben