January 20, 2006 | By: Aimee Nielson

With many of Kentucky’s agricultural producers adding grapes to their enterprises, educational opportunities about the growing process and making wine are becoming more abundant. 

One of those opportunities took place recently at the Kentucky Fruit and Vegetable Conference, with University of Kentucky Extension Enologist (winemaker) Tom Cottrell telling current and potential grape growers about the key steps in winemaking and how to avoid common wine flaws.

“There are seven key steps in winemaking, but I want to focus on what I think are the most important,” Cottrell said. “Sanitation and avoiding microbes is very important as is accurate laboratory work and determining ripeness; however, the cornerstone of maintaining wines from bottle to sale is ‘free’ form sulfur dioxide, or SO2, management.”

Because microbe sources are everywhere – in grapes, machinery, pumps and hoses, tanks and barrels – producers must make sanitation a priority, he said. Cottrell emphasized that “free” form SO2 is really what works in avoiding and controlling bad microbes and that it also prevents premature oxidation in the winemaking process. 

“Winemakers should pay attention to pH changes during fermentation and cold stabilization,” Cottrell said. “It’s not the end of the world to have a high pH, you just need to add enough SO2 to compensate.”

Cottrell coined his own term, “the Cottrell Rule,” to help producers understand just how much SO2 to add during the winemaking process. He said if pH is 3.56 for example, 56 parts per million of SO2should be added. The amount of SO2 is always equal to the numbers after the decimal. (If ph is 3.XY, SO2 should be XY.)

Cottrell also identified sources and causes of common wine flaws. The grapes themselves can be a source as well as how they are processed. Prefermentation treatments and yeast selection also can be sources of flaws.

“It’s important to make sure the grapes are ripe; get them clean,” Cottrell said. 

He said one advantage Kentucky wineries have is that they are small and the grapes are handpicked. Handpicking allows the picker to sort out the rotten fruit before it makes it to the crushing floor. Cottrell said if incoming grapes have defects of more than 3 to 5 percent, producers should add 50 ppm of SO2to avoid processing delays.

“Make sure you avoid things that encourage bad microbes like temperatures above 65 degrees Fahrenheit, old barrels and poor sanitation,” he added. “Simple things like good SO2 levels, cool temperatures and good sanitation can help you control microbes and avoid many common flaws.”

Cottrell is UK’s first enologist. He was hired, along with viticulturalist (grape-growing specialist) Kaan Kurtural, to meet the research and Extension needs of Kentucky’s fast-growing grape and wine industry.



Tom Cottrell 859-257-0037