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The Winemaker’s Think Tank: Vol 15 – How to work with Frozen Must

Wine expert testing wine silhouette image

What’s the Winemaker’s Think Tank?

Every Thursday we will post about a few frequently asked questions that our winemaker has answered. If you have a winemaking question you would like to have answered, please email us at support@juicegrape.com and we will try to get into next week’s post. Cheers! 🙂

Simplifying Your Life with Frozen Musts

Life gets hectic. We totally understand. As the Fall and Spring wine grape harvest seasons approach, not everyone can just suddenly stop their normal life and shift into winemaking mode. Kids, vacations, work, weather and a myriad of other obligations can impact the ability of a winemaker to start a particular year’s vintage. And let’s not forget about those grapes – unfortunately they don’t seem to care much about your schedule. They ripen and arrive when it’s convenient for them, not for us. Fortunately there is a way to work with grape varietals anytime you choose by using frozen must.

Frozen must is exactly what it sounds like – fresh grapes that have been crushed and destemmed on site into must and then immediately frozen. Working with frozen must is very similar to working with fresh grapes, but there are some differences that winemakers should be aware of. With frozen must there is no need to take your crusher/destemmer out of storage and lift those heavy boxes of grapes into the machine. This part of the process is done for you already. If you were working with fresh grapes, the resulting must would be adjusted and then the winemaker would start the fermentation process. Yet by freezing this must we are basically halting the winemaking process by putting this must into a deep freeze – then the winemaker can thaw the must and continue the process when it is convenient for them.

frozen must 1

Besides the convenience of making wine around your schedule ( with less equipment and less preparation/cleanup), there is another helpful benefit when working with frozen red varietals – cold maceration! During the freezing and thawing process the prolonged skin contact at cooler temperatures can maximize color extraction. Additionally, the tannins extracted during this time are water soluble and will be softer than the harsher, alcohol soluble tannins imparted during primary/post fermentation maceration. Now that we have touched on the benefits of using frozen musts, let’s transition to working with it.

When you receive the pails/drums of frozen must, we need to get the must thawed and up to fermentation temperatures safely. All of our musts are sulfited to 50ppm – this will help to control any oxidation that may take place during the thawing process and also help to limit the formation of bacteria in the grapes. However it is still possible for some freezer-burned or moldy grapes to be present – remove any grapes that look questionable. Some winemakers like to slowly bring the must up to temperature over the course of several days, while some recommend getting to pitching temps as quickly as possible. A slow temperature rise will prolong cold maceration and its benefits, but remember that the must is susceptible to unwanted bacteria and other bugs until primary fermentation starts. We recommend keeping the pails at room temperature – they should thaw out in 2-3 days.

It is important to stir the must as it is thawing. During the freezing process it is common for the natural sugars and potassium bitartrates to settle at the bottom of the pail (very much like the frozen Italian ice cups you can buy in the supermarket. The best part is the bottom of the cup where all the sugary, sweet goodness has settled to). Stirring the must with a clean and sanitized utensil daily will help homogenize it so that it thaws evenly. Once the must is at pitching temperature, empty the pails into your primary fermenter and treat it just like you would freshly crushed-destemmed grapes. Remember to get all the juicy bits and tartaric crystals from the bottom of the pail! We recommend taking pH, TA, brix, and S02 readings and adjusting accordingly. These readings can vary based on the temperature of the must and how well it has homogenized during the thawing process, so it is best to wait until the grapes are at room temperature. While we will always recommend using commercial yeasts to help with a steady, clean fermentation, it is very important to use these types of yeasts when working with frozen musts.

So there you have it – using frozen must can simplify a winemaker’s life by making it easier and less hectic. Isn’t that what we all hope for during the harvest season?

(A big thanks goes out to Robert Herold for his original article Winemaking From Frozen Must which appeared in the December 2012 issue of Winemaker Magazine)

We hope this information helps with your winemaking. If you have any follow up questions or winemaking questions in general, please email us at support@juicegrape.com.