Wine Enthusiast Magazine
SubscribeNot long ago beliefs that could easily have been labeled superstition governed a lot of what happened in vineyards and wineries. If deer were eating your grapes, you didn’t build a fence to get rid of them, but you shot one of them, cut the carcass into chunks and hung the chunks from trees at strategic spots around the perimeter of the vines. The deer would get the idea.
Grape growers in California used water witchers to find where to drill for water. Vignerons in France wouldn’t let women into cellars because they believed that if a woman was having her period it would spoil the wine.
It seems like one current superstition going around is that yeast has gotten stronger in recent years, and that explains in part why wines are higher in alcohol. Tim Patterson did a great job of debunking this myth and has gotten a lot of compliments and commentary on his investigation.
See, every winemaker used to learn that yeast converts sugar in the grape juice into alcohol at the rate of 55 percent. If the crushed grape must for reds or pressed grape juice for whites measured 25 degrees Brix (same as 25 percent sugar), then the winemaker mutltiplied by .55 to predict the eventual alcohol content of the wine. So, 25 times .55 equals 13.75 percent alcohol.
Winemakers however, have come to believe that the yeast of today have been working out at the gym. I’ve heard many of them say that the conversion rate has gone up to .60, which would give them 15 percent alcohol from the same juice. That’s a significant difference, going from moderate to high alcohol in one leap of folklore.
Patterson explains how the yeast manufacturers have studied the situation and say it isn’t so. Yeasts are very ancient organisms that work on a molecular level, and after millions of years they haven’t changed their habits. It may be, instead, that winemakers aren’t getting accurate readings of the real sugar content in their musts.
In some cases, it may be that the ghost conversion rate of .60 is just a more comfortable explanation for the high alcohol levels of their wines than admitting that they’re waiting to pick the grapes until they’re approaching 28 degrees Brix. I think it’s a case where a little more science needs to be applied to the situation.
Filed under: Industry Issues
17 Comments
September 19th, 2007 at 11:06:15 AM
It’s odd that it was the winemakers themselves who made the claim that yeasts are more powerful. After all, it’s not something a wine writer would make up! Why would winemakers say something that’s objectively not true [if, in fact, Patterson's analysis is correct]? Two reasons, as far as I can make out. One, the yeast manufacturers made that claim in their marketing. Two, enology professors supported it. In a 1999 issue of “Wines & Vines,” a famous UC Davis enologist cited the “Importance of new wine yeast strains for increased ethanol tolerance [leading to] increased flavor and odor components.”
September 19th, 2007 at 1:02:13 PM
Steve: Yes, there are new strains that can deal with the higher alcohol levels in fermentors. They stay viable and keep converting sugar to alcohol and carbon dioxide even when the must gets up to 16 or 17 percent alcohol. Some older strains die off before then. That doesn’t mean those new strains would convert at a higher ratio. Just that they can deal with musts that are going to end up very high in alcohol. The new yeast strains would still convert 25 degrees Brix to about 13.75 percent alcohol, just as the traditional strains would.
September 19th, 2007 at 6:00:25 PM
Jim: I couldn’t understand this more efficient yeast explanation either. I first saw it in a post on Jo Diaz’s Juicy Tales (http://www.wine-blog.org/?p=163).
Maybe one explanation for the use of 0.6 as the rate of conversion came about because someone decided to round up 0.55 to a single decimal point!
In any case 0.55 to 0.6 does not seem to be a big difference. But that will depend upon the accuracy of the technology used to arrive at 0.55. The use 0.6 might even be acceptable if the range of values originally determined for the rate of conversion of sugar to alcohol were 55 +/- 5! But of course when its equated with a change from 13.75% to 15% alcohol, well then the wine world starts to buzz!
September 19th, 2007 at 7:05:16 PM
Doesn’t sound accurate to me…The climate is warmer and growers can wait longer to pick…I thought the West Coast was going to burn off the map this summer! Also, you would think there would be thecnology to get accurate readings of the sugar levels? Cheers!
September 19th, 2007 at 7:25:35 PM
Tim Patterson’s point is that it’s the riper fruit that is making alcohol going up, not better yeast. And I don’t know which West Coast you’re talking about. It’s not been a hot summer here in Napa. Just two noticeable heat spikes. We only needed to run our home AC about 8-9 days all season. Harvest started early because of the early spring and early bud break.
September 19th, 2007 at 7:28:32 PM
It’s a bit off topic [sorry!] but since our West Coast weather came up, I’m of the opinion that the last 3 vintages [2005, 2006, 2007] have been quite cool, at least compared to the previous vintages. The interior West has been very hot, but not the immediate coastal strip of California, which is where the prime grapegrowing is.
September 19th, 2007 at 9:05:59 PM
Point taken I am an East Coaster….I thought I read aricles that the regions North of L.A. were going to run into trouble because of the Heat? Enjoying the Blog Jim!
September 20th, 2007 at 8:48:02 AM
In addition to brix, we have glucose/fructose analysis run on all of our juice samples. This is a standard analysis in a juice panel at a very well respected wine lab.
The glucose/fructose (g/f) content of the juice (measured in g/100mL) has shown to be a more accurate indicator of the fermentable sugars than brix. The g/f is typically 4%-5% higher than the sugar level indicated by the brix measurement (which measures all soluble solids, not just fermentable sugars).
This particular lab estimates alcohol levels at 0.595% of the measured glucose/fructose. We’ve found these conversions to be more accurate and consistent than the conversions based on brix alone.
I don’t propose the above as a cause of higher alcohols, just a winemaker’s observation that seemed relevant to the discussion. I agree that the single most significant cause of higher alcohols is riper fruit with higher sugars.
September 20th, 2007 at 9:30:09 AM
To clarify a point I made above :
When I say that the glucose/fructose level is 4%-5% higher than the brix reading –
This means that a brix reading of 25 degrees could have a corresponding glucose/fructose of 26 g/100mL(26 being 4% more than 25). 26 is the number I would use as my sugar reading.
Cheers,
Chris
September 20th, 2007 at 10:02:40 AM
Chris is the winemaker at Monticello Vineyards / Corley Family winery in the Oak Knoll district. His winery is one that practices moderation in alcohol content. Thanks for contributing, Chris.
September 20th, 2007 at 12:05:42 PM
Just a comment on the blanket statement “…interior West has been very hot…” I can’t speak for the Central Valley, but the southern Foothills have been quite temperate again this year – with the two hot spikes that everyone got. In fact, we’re kind of annoyingly cool right now – yesterday’s high was only 63 – and especially since we’re planning an outside wine dinner this Saturday!
September 20th, 2007 at 12:33:32 PM
Always nice to see yourself talked about in cyberspace. On the coastal / interior theme, for what it’s worth, I was chatting about all this with Jim Clendenen of Au Bon Climate in Santa Barbara about all this the other day, and he’s convinced that the short-term global warming pattern is that the Central Valley sucks up all the heat and leaves the coastal valleys, al least the ones in Santa Barbara, cooler — their harvest is looking late this year.
September 20th, 2007 at 1:40:14 PM
the change in the conversion rate has nothing to do with how efficient the yeast are but rather how determined the yeast are. they convert MORE sugar to alcohol than the native yeasts therefore increasing the alcohol level. where a native yeast would tire out and STOP converting sugar to alcohol the new super yeast just keep on going…kinda like the energizer bunny.
September 20th, 2007 at 2:42:20 PM
Just to clarify: By “interior west” I mean the Great Basin, AZ up to Montana, not the Central Valley of California.
September 20th, 2007 at 9:34:48 PM
I do agree with Mr. patterson about being able to pick later as being the reason forthe higher alcohol levels in wines….What I don’t understand is why are these wines being critized so heavily for being higher in alcohol? It just makes everyone think of excuses for the higher alcohol levels in wine…as if the winemakers are doing it on purpose with these “super” yeasts. As a winemaker I would think you would pick when your fruit is as ripe as it can get? I guess in the past it was just too much of a gamble to wait(resulting in lower alcohol wines) but now that we have a changing climate it sin’t so much of a gamble and therefore the higher alcohol levels are as it should be. Your toughts? Cheers!
September 21st, 2007 at 9:35:59 AM
Kevin: You’re about right on this. The criticism about high alcohol content comes on the one hand from some consumers, sommeliers and critics who think that lower-alcohol wines are more classic, more European in style, more refreshing and, on the other hand, from daily wine drinkers like me who like to have three or four 4-oz. glasses in an evening. Jumping from the old 13.5 percent alcohol level of 10 years ago to the current 14.5 or 15 for many Californian wines is a leap from a good night’s sleep to a mild hangover for us.
September 21st, 2007 at 10:37:24 AM
I have been making wines for almost thirty years and what I was taught in school, a 0.50-0.55 conversion rate, is nonsense. I typically see a conversion rate of 0.62-0.64. My girlfriend, Kris Curran, picks her Grenache Blanc at around 23 Brix and ALWAYS gets over 14% alcohol. You do the math! As far as the “more refreshing European wines”: they can’t get their sugars higher in normal years, hence the reason to get it from a bag or a concentrator. France has their best vintages when the weather mirrors that of California; let’s face it, we have consistantly better growing seasons which leads to better wines. And, if you need to get your sugars up to get your tannins ripe then you can’t be weak minded about adding water to your fermenter. Have some balls!