Preparing White Juice for Fermentation05/09/2012
White wines are made using only the juice from the fruit, the solids are not included. In order to separate the juice from the solid parts of the grapes, we must crush and press the grapes before the fermentation begins. Once we the juice is processed (also called "must") we test the pH, TA, and ºBrix. pH and TA are measures of acidity, while the ºBrix tells us how much sugar is in the juice. There are general ranges where we would like each of these to be in order to create a nicely balanced wine. If the pH, TA or ºBrix of our juice happens to fall outside of the recommended ranges, we will need to adjust them (determining and adjusting these factors will be explained in detail later). Then, yeast is added and fermentation begins. These steps make up the basic foundation of white winemaking and will be the focus of this chapter. In addition, there are a few "advanced" processing steps that we can incorporate into this basic foundation which can really help improve the stability and overall quality of our finished wines. These "advanced" techniques are not hard to do, but success lies in understanding what is required from a technical standpoint to avoid doing more harm than good. Let’s take a closer look at how everything comes together.
We Picked up the Fruit!
Ok, so you’ve harvested your fruit or purchased some grapes and brought them home. First, examine the fruit and remove any raisined or rotted/molded clusters. Hopefully the grower will have picked the fruit when the sugars are in the correct range (17°-24° ºBrix*). You can request this service, so don't be afraid to ask. If the sugars are outside of this range, you will have to address this after the crush. (Either by adding sugar to raise the ºBrix, or by diluting the must to lower the sugars. See our Guide to Dilution and Chaptalization for a full explanation of adjusting sugars.)
*Note: Brix is the scale most often used to measure sugars in winemaking: 1ºBrix = 1% sugar (wt/vol), or 1 gram sugar in 100 mL. You can measure ºBrix with a refactometer (MT700) or a standard hydrometer (MT310) - just take your reading off of the ºBrix scale and not the Specific Gravity scale. The grower or your source for the grapes should be able to tell you the ºBrix level because this should determines when they are picked.
Prepare to Fill the Press: Crush and De-Stem the Grapes, or Leave as Whole Clusters
When processing white wine grapes, there are two options; either crush and de-stem them first or just add them straight into the press. The pros and cons to both techniques are listed below, but for the most part the majority of white wines are made by de-stemming and crushing before going into the press.
Note: Whichever method you choose to obtain your juice, we recommended processing the grapes cool if at all possible (50-55F). Doing so will help retain delicate aromatics in the final juice, slow oxidative reactions, and help the SO2 delay any unwanted microbial activity! Picking/processing early morning or at night is a very effective means of achieving this. If you are lucky enough to have access to a walk-in fridge/freezer this is a great way to get the grapes cool before processing. However, you will need to make sure they don’t get too cold either or the yeast may have a hard time getting started!
Crushing before pressing:
Since you will be pressing the fruit anyway, the berries don’t need to be completely mashed – just removed from the stems. For small amounts, this can be done by hand. If using a crusher-destemmer, unwashed grapes are added directly to the top hopper on these machines. The grapes are crushed by the rollers and fall through the grate below into your fermenter. The separated stems are ejected out of the unit by the “destemming bar.” These machines are available in manual and electric versions. The combination of juice, skins, seeds, and pulp that falls into your holding vat is now called “must”.
- Allows winemaker to work with skins if desired (so any style of wine can be made).
- No fear of extracting harsh stem tannins during pressing.
- Requires crusher-destemmer.
- Exposes juice to oxidation before it gets to the press (this can be avoided and we’ll explain the techniques needed to protect against oxidation in the next section).
- Some grapes may clog the press and require multiple breaking-ups of the press cake in order to drain completely (this can be addressed by adding rice hulls or a portion of the stems along with the must when filling the press; see "pressing" section below).
Whole Cluster Pressing:
Not all white wine grapes are destemmed before being crushed. In fact, Champagne production exclusively uses whole-cluster pressing. This creates a delicate, lighter-styled wine that is great for making sparkling wines, but if you are after something that will be more full-bodied, destemming and crushing before pressing may be a better choice. However, if you do choose to whole cluster press, remember that the presence of the stems can create an over extraction of harsh tannins and other potentially undesirable compounds if you squeeze the fruit too hard. Remember to taste often once the pressure is being applied during the press cycle to avoid
picking up too much astringent/green characteristics in the pressed juice.
- Does not require a crusher-destemmer.
- Limits the juice exposure to oxidation before going into the press.
- Stems help the press cake drain completely, increasing the yield of juice/grape solids.
- Does not allow winemaker to work with skins, can only make light and delicate wine.
- Very possible to extract harsh stem tannins during pressing.
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