Freeze effect on grapes

Ice wines are made from grapes harvested and pressed at tempertures near -10C after three consecutive nights of such conditions ( I've seen vineyards wait until january in order to harvest an ice wine juice). The resulting juice is more syrup than juice and volume yield per ton is very very low. Late harvests are usually left hanging a little longer than ripe till just about raisins on the vine. The longer you hang the higher the sugar and lower the water and acid.

You can adjust the Ph afterwards and start with grapes with naturally high SG. The longer you wait for harvest the greater the loss to birds, bugs, and any thing else. High risk and low juice yield drive up the prices of ice wines and late harvests.

Thanks for the info! At what temperature and for how long before the grape taste changes? Last year I left some grapes hanging and when I finally got around to checking on them I noticed the taste had changed completely from a fruity taste to a jammy flat taste. The berries were not shriveled yet. I think this would affect the wine taste. I guess this would be o.k. for ice wine or late harvest wine since the high sugar masks the flavors but I am wondering how long can I let them hang before the "taste change" happens. I am trying to lower the TA slightly since last year I ended up with high levels of acidity.

Sarge wrote "Does anyone have ideas on what effect frost has on grapes such as Baco Noir...I am only looking to lower the acid a bit not to make a sweet wine. When should I pick them so I don't loose the normal varietals taste?

At what temperature and for how long before the grape taste changes? Last year I left some grapes hanging and when I finally got around to checking on them I noticed the taste had changed completely from a fruity taste to a jammy flat taste."

Sarge - I grow Baco here in the Kansas City area. I figure I'm doing good if the acid drops to 1.0% by the time I pick. Harvest has brix about 22 and as high as 26 one year. I think pH is more a problem with Baco than acid or brix. If pH rises much above 3.5 the wine takes on a brownish tint. My vines are 8 years old and the wine made from these grapes the last two years has been much better than when the vines were younger.

With respect to how long you can let hang without losing the fruit taste...the only way is to taste them as the summer goes along. But, I picked some two weeks ago and they were still fruity.

Where do you grow these grapes? Do you test for sugar, pH and TA periodically and balance those test results against grape flavor?

If you want to taste a really great Baco order a bottle of Chateau Loraine

These people really know what they are doing with the grape but they are in Oregon, not Kansas.

BTW, if you are unhappy with Baco wine, save the vines an just make grape juice. It's the best tasting grape juice I've ever had.

Bill Frazier Olathe, Kansas USA

The change you noticed is most likely a matter of balance. As the grapes hang on the vine, the sugar increases and the acid decreases. The acid present in the fruit gives the perception of freshness to the fruit flavors. As the acid level drops or as acid precipitates due to colder weather, the lower acid level can give way to what is perceived as a jammy taste but it can simply be the result of change in the acid/sugar balance. Adjusting the acid level of the must prior to fermentation can ensure you still get a balanced wine with good fruit character. From what I understand, many California wineries let their grapes hang to sugar levels as high as 30 brix. This fruit would undoubtedly taste jammy but balance would be introduced through addition of acidified water.

Regarding icewine, winemakers to make it in Canada will tell you that the flavors indeed change after the grapes are affected by several freeze/thaw cycles. I think this has more to do with the rupture of skin cell walls and release of aroma precursors into the juice than actual changes in the chemistry of the precursors.

In any event, it would be a cool exercise to pick some of your grapes before and after this perceived change and adjust the must of each to the same sugar/acid level prior to fermentation and then compare the results.

CHEERS!!

Aaron

Hi Bill I am near Niagara Falls. Last year the Baco Noir were quite tart. Of course it was a terrible year here. The initial TA was 1.4% and Brix 22. This year was much better. My 100 Baco plants are 5 years old and are quite productive but not too vigorous. I also grow some cab, chardonnay, merlot and pinot noir. I am converting an old concord vineyard and still have 2 acres of concord to convert. Concord makes a great juice. I can't decide what to variety to grow. I rely a lot on the stem and seed colour and the taste for harvest decisions. I have difficulty accurately measuring TA in reds. Sarge

Hi Aaron

Your explanation makes sense! When you say acid decrease occurs are you referring to tartaric acid precipitating within the berry? Would this go back in solution later when you crush? Is there other acid reductions also going on during freeze cycle? You mentioned that when grapes freeze/thaw the cell walls rupture. Do you know what temperature is needed for this?

I made a batch of Baco last week and left enough for another batch hanging. I may wait until the first freeze and then make another batch. Of course the grapes will ripen further and shrivel a bit resulting in higher Brix.

Sarge

Hey Sarge,

Acid reduction occurs during ripening as berry respiration of Malic acid causing its reduction. During cold temperatures, precipitation of potassium tartrate and malate and the mixed salt can occur and may be largely permanent. I am not aware of any other mechanisms for acid reduction other than these. I am also not sure of the temperature required to rupture cell walls in the grape skins but I imagine it would occur as soon as water in the cells freezes, probably not much below freezing would have some effect.

I look forward to hearing how your experiment goes. To keep it "real", I suggest you adjust the two batches to as close a starting brix/acid as possible.

Good luck!!

CHEERS!

Aaron

How about trying something different like Petit Manseng for icewine??

Aaron

Interesting suggestion? Of course ultimately it depends on your market and what you can grow. I am not aware of anyone growing Petit Manseng in Niagara but I did hear it does well in Virginia due to the extended growing season and low chance of late spring frost. In Niagara I see growers sticking to a few well understood varieties. (cab franc, riesling, gamay, chardonnay, pinot blanc, pinot noir, merlot, cab sauv., vidal, baco noir, foch, gewurztraminer...) I heard of a few growers trying pinot gris, zinfandel and nebbiolo. I don't know how they fared. Here, we are tested by severe winters from tme to time and late spring frost. Of course vnifera is not an option once you move away or north of lake Ontario. There areas that are doing quite well with cold hardy french hybrids there.

Sarge

Below -5 celcius is when ice will form in the berry.

Thanks for the info J F! I would guess that as long as the temperature stays above -5 (-4 to be safe) then you could let the grapes hang and not get a dramatic change in taste due to temperature. In the Niagara area we usually get frost in early October but the cab sauv are left into November some years.

Bill I thought Baco was usually high TA. Why would PH be an issue? Does the PH increase if you let them hang too long past ripe or are they prone to acid imbalance high TA and high PH? Would you share how you make Baco wine?

Sarge wrote "I thought Baco was usually high TA. Why would PH be an issue? Does the PH increase if you let them hang too long past ripe or are they prone to acid imbalance high TA and high PH? Would you share how you make Baco wine?"

I have 24 eight-year old Baco Noir vines, 8 feet apart growing on a single wire 6 feet high. Unlike yours mine are very vigorous...like Kudzu. When are they ripe...that is the question. They contain so much acid that the tartness can mask the fruit flavor. As acid falls pH rises and Baco wine with a high pH is brown...it's ugly.

I figure if I can pick Baco with the acid near 1.0% I can make a decent wine. For instance in 2003 I picked at 26.2 brix (way too high), 3.52pH and

0.97%TA. I did nothing to the must before fermentation. I fermented with Lalvin BM45 yeast, DAP, Fermaid and pectic enzyme for 7 days on the skins at room temperature. The new wine was pressed off the skins and malolactic culture was added. The wine was racked to very full carboys until ML was complete. The wine was very dry, had a deep red color and tested at 3.68pH and 0.84%TA. Cold conditioning knocked the TA down to 0.75%. At this stage my notes say "Very good red wine taste. Could bottle now without any oak exposure." I put the wine in a 10-gallon Gibbs Brothers oak barrel for a couple of months and it took on a nice oak flavor. Turned out to be the best Baco I've made although too alcoholic.

This year I picked the Baco October 7th...weeks later than usual. pH was

3.55 and TA was 1.1%. All my grapes were late this year...cooler summer and lots of rain. Just to be sure the wine doesn't finish with too high pH I added tartaric acid to lower starting pH to 3.42. This pushed TA up but I'm confident the excess will ppt out with cold conditioning. Same winemaking routine. Time will tell.

The key is getting grapes with TA at or below 1% acid. To help achieve this I leaf pull around the clusters so they get a lot of light. I trim off some of the shoots to further improve light penetration to the grapes. I cluster thin to 2 clusters per shoot. I never fertizize Baco.

Bill Frazier Olathe, Kansas USA

Thanks for sharing Bill!

Has Niagara region had a frost on the vines yet? I haven't notcied anything here in St Catharines.

If you are going to let the clusters hang past leaf drop the berries will change to a low acid jammy thing that is only good for sweet late harvests or ice wine if it gets cold enough.

Hi J F I have seen white condensation on roof tops twice but the cab sauv are still growing although I may pick today. I haven't seen frost damage on grape leaves yet. One thing I am curious about is if the acid drops and some varieties are prone to browning with high PH. Then does the ph have to be adjusted before making late harvest or ice-wine? Sarge

"> Hi J F

I have seen ice wine made from chard, kerner, vidal, rielsing, semillon, pinot blanc and few others and all of them are straw to amber in colour, I haven't seen an ice wine that is very light in colour most if not all of them have heavy colour. I'm not sure if this is fomr oxidation or from skin contact while the grapes are wilting on the wine.

thanks J F!

My memory is failing but isn't it only 14 or so leaves per cluster is all you need?