Sweet Wines - Dehydrated and Frozen Grapes

Sweet Wines - Dehydrated and Frozen Grapes

A colleague of mine went to the RBHK Restaurant & Bar Exhibition held on September 5-7th at the HKCEC (Hong Kong Convention and Exhibition Center), and came back to me the next day with an interesting question related to sweet wines.

He went to a booth where he tasted an Australian sweet wine made with dehydrated grapes and had no clue that such wine existed, thus he came back to me the next day at work and asked me about how it was made.

His question sparked me to write this post for those of you who might also have an interest in knowing how sweet wine can be made from dehydrated grapes and other techniques like frozen grapes.

As usual, I tried to answer him by keeping my explanation as simple as possible (yet detailed) and will now try to re-transcribe it in this post.

Sweet Wines

Sweet Wines are all about sugar...

Sweet Wine Metaphor by LeDomduVin © 2017

Sweet  wines are usually made with grapes that have high level of sugar and/or can be produced via different methods of vinification/fermentation processes that may include addition of sugar or substitutes.

The Grape Berry Content - LeDomduVin 2017 ©

High level of sugar in the grapes can be obtained by 3 common methods (detailed further below):

• Leave the grapes longer on the vines until they get affected by the Botrytis Cinerea (Noble Rot), lose their water and shrivel, in order to only collect the remaining concentrated sweet juice/nectar inside   

• Leave the grapes on the vine until the first frost of the year, in order to freeze the water inside the grapes and only collect the unfrozen concentrated sweet juice/nectar inside  

• Harvest the grapes at ideal or full maturity then air dry them on straw mats outside under the sun or within special facilities, then press them or add them to the must to enrich the wine and increase its sugar level prior, during or after fermentation 

The sugar being transformed into alcohol by the yeasts, the grapes must be fully mature/ripe and the  sugar content high enough to achieve both the desired alcohol and sugar levels in the final wine.

NB: Yet, sometimes, the sugar content into the grapes is not enough and an addition of sugar (or substitutes) is needed to concentrate the sugar level in order to obtain the desired style/type of wine to be produced.

Grape Berry Degrees of ripeness and evolution from dry to totally shrivelled

Tokaji Aszù Furmint Grape
Degrees of Ripeness and evolution from dry to a "Aszù Berry"
- Courtesy of Disznoko Winery (Hungaria)

At Harvest Time

The ideal level of sugar in the grapes consequently depends on the harvest time and consequently on the desired wine style/type to be produced.


1.  Late Harvest (Vendange Tardive in French or Spätlese in Germany)

Leaving the grapes on the vines to mature longer to obtain a higher sugar content and thus harvest later than the usual harvest time for dry wine (roughly about a few weeks to 1 month later depending on the producer style and wine style/type to be achieved). Usually white wines made out of grapes such as Riesling, Gewurztraminer, Muscat, Semillon, etc.. a few notable reds too made from Mourvedre, Zinfandel, Grenache...

The most notable and recognized being German and Alsace (France) Riesling and Gewurztraminer wines. Yet other wines from other regions in the world made with Semillon, Muscat, Muscadelle, Vidal Blanc, etc.. are also worth a shot.

Late harvest Riesling grapes on the vine at Colloca Estate Winery in Fair Haven, NY via Pinterest

Late Harvest - Semillon Grapes prior Botrytis Cinerea
Courtesy of www.chateaucoutet.com

2. Noble Rot (Pourriture Noble in French or Muffa Nobile in Italien)

Same as Late Harvest, but the harvest occurs later (roughly about 1-2 months later than for usual harvest time for dry wine) when the grapes, affected by the Botrytis Cinerea (Noble Rot / Fungal Infection) are shrivelled and desiccated. Basically, they are dried out of their original water content due to the fungal infection and thus water evaporation. The grape skin being damaged, it cannot retain the water inside anymore and start to shrivel, thus increasing the sugar level in proportion of the remaining juice inside.

A few examples:

• Sauternes-Barsac (Bordeaux, France)
• Coteaux du Layon (Loire Valley, France)
• Monbazillac (Dordogne, France)
• Tokaji Azsú (Hungary)
• Riesling Beerenauslese and Trockenbeerenauslese (Germany/Austria)

Noble Rot - Semillon Grapes partially affected by the Botrytis Cinerea
Courtesy of www.chateaucoutet.com

Noble Rot - Semillon Grapes fully affected by the Botrytis Cinerea
Courtesy of www.chateaucoutet.com

3. Ice Wine - Naturally Frozen Grapes

Usually made out grapes growing in cooler climate regions (Canada, Northern US, North-Eastern France, Germany, some countries in Eastern Europe, South Australia, New Zealand, etc..) where the grapes left to froze on the vines will reach full maturity and the whole berry will freeze with the first frost (or cold temperatures) and ice formation of early winter (usually when temperatures have reached around -5 to -8 C°).

It can only happen in certain countries/regions and during certain years when the frost occurs prior the grapes get affected by rot (usually ice wines are made out of non-botrytised grapes free or only partially free of rot). The grapes are manually harvested and then delicately crushed/pressed to extract the undiluted nectar full of sugar (as the water inside grape freezes).

The most notable examples come from Canada, Germany (Eiswein), Eastern Europe and South Australia with occasionally some from France (when the weather is cooperating), made out of white grapes such as Riesling, Gewurztraminer, Gruner Veltliner, Pinot Blanc, Chenin Blanc and Vidal Blanc...even Seyval Blanc, Chardonnay, Kerner... A few notable red ice wines are also made out of Cabernet Franc, but other red grapes like Pinot Noir, Merlot and Cabernet Sauvignon are also used in some countries.

Frozen Grapes - Courtesy of www.today.com

Frozen Grapes under the Snow - Courtesy of blog.eckraus.com

Various Kinds of Ice Wine - Courtesy of Wine Folly (www.winefolly.com)

4. Artificially Frozen Grapes

For grapes growing in warmer climate, as frost rarely occur prior the grapes get affected by rot, the grapes are left on the vines up to optimum maturity (depending on the desired brix (*) level, harvested, then put into racks or boxes that will be stored into freezer to obtain the same result as naturally frozen grapes. The wines produced with methods cannot be called Ice Wine, in the US they are sometimes referred to as "Icebox" Wines.

(*) Brix: a unit of measure of the sugar content of grapes, must and wine, indicating the degree of the grapes' ripeness (meaning sugar level) at harvest)

FYI: Fractional Freezing and cryo concentration have also been used for decades to increase the concentration of grape juice and musts, and thus sugar level (but this could be the subject of another post maybe).

5.  Air Dried Grapes

Usually for grapes growing under warmer climate, the grapes are picked at perfect maturity (or slightly earlier or later depending on the producer style and wine style/type to be achieved), then the water contained inside is removed by air drying the grapes to make raisins either by leaving the grapes on the vines (the berries must not be too close to each other to let the air flow) or put them on straw mats (usually under the sun). The shriveling and desiccating of the grapes occur naturally during a drying period which can go up to 120 days.  

6. Artificially Dried Grapes

Same as for Air Dried Grapes except that the drying is done in special drying chambers under controlled conditions. This method minimizes the amount of handling of the grapes and helps prevent the onset of rot (like the Botrytis cinerea) or other external degrading factors (bird, disease, rain, hail and/or mold) which could damage the grape's skin. For the wine produced from these raisin grapes, the quality of the grape skin is a primary concern, as its component brings the tannins, color, and intensity of flavor to the wine.

7. Dehydrated Grapes

Examples of Late Harvest Wines (including Icewine and Passito) from Richer to Lighter -
courtesy of Wine Folly (www.winefolly.com) 

At Fermentation Time 

1.



The 5 types of Dessert wine are: Sparkling Dessert Wine Lightly Sweet Dessert Wine Richly Sweet Dessert Wine Sweet Red Wine Fortified Wine




🔺Work in Progress..... to be finished soon🔺







Santé! Cheers!

LeDomduVin a.k.a Dominique Noel
Sommelier | Wine Quality Control Director | Wine Buyer | Market Analyst

#ledomduvin @ledomduvin #dominiquenoel







(*) Thanks to Madeline and her team at Wine Folly for the pictures, you did the job for me so I figure it will be easier to just put your pictures 😊😉 I have been a great fan from the very beginning.