From fermentation temperatures to barrel choices, there are plenty of considerations up and down the line at a winery that help to define quality. However, for those winemakers who want to keep everything in balance, there's a decision made during the first five minutes after harvest that sets up everything to follow. By properly destemming and crushing grapes, winemakers facilitate tannin structure, color extraction and aging potential. Fail to do so and you've created uphill battles through every subsequent step.
Yet from the outside, destemming appears pretty basic. Grapes come in one end, the stems come out the other side, juice is collected in tanks for fermentation. Simple. Until you learn that the pressure, speed, and complete destemming (or lack thereof) impacts phenolic inclusion that cannot be reversed in the cellar.
Why Stems Matter More Than You Think
Grape stems are not just part of the plant that needs to be thrown away. They are tannins, and tannins that operate differently than those found in skin and seeds. Tannins from stems tend to be astringent, green-tasting and even less likely to soften with age. Thus, in small, intentional inclusion, they can lend structure and complexity. In unintended proportions, they emerge as harsh and vegetal features that dominate through quality assessment.
But getting completely rid of the stems does not equate to no stem involvement. The best machinery on the market for destemming still leaves some pieces left behind—and often this is a good thing. Control is the name of the game; you're better off making the decision about how much stem character enters the must before leaving it up to your destemming device based on what's left behind.
Each varietal yields varying results from stem inclusion. Whole cluster Pinot Noir producers do so because of the structure and spice that stems can lend a wine. But Cab producers who produce whole cluster run up against unintentional bitterness. It's not about destemming per se; it's about intentional control over what stems can do.
The Pressure of Crushing and Destemming
Usually destemming and crushing occur simultaneously; however, this is a separate operation with different implications for quality. Crushing serves the purpose of breaking apart berry skins for juice production. However, the harshness in which this occurs influences everything from color extraction to seed tannins.
Less aggressive crushing reduces seed breakage and prevents bitter compounds from being extracted. However, more aggressive crushing allows juice release at a quicker rate but increases risks for astringency via crushed seeds and excessive skin maceration. For professional winemakers using a grape crusher destemmer, they can customize levels of pressure to reflect their equipment settings for stylistic approaches and condition of fruit entering.
Crushing pressure is contingent on weather conditions at harvest. Healthy grapes with intact skins can survive more aggressive crushing than sad grapes with bruised skin, dry out levels, or even those infected with mold. Equipment that boasts adjustable crushing potential allows this type of standardization.
Processing Speed and Temperature Management
The speed at which grapes move through destemming systems and into crates impacts juice temperature and oxidation and microbial growth. Slow systems allow too many enzymes to induce browning or starter fermentation; fast systems produce heat via friction which increases temperatures enough to kick off fermentation early or kill native yeasts an operator wanted to retain.
Most quality defects during processing are temperature-related. Grapes that sit too long in bins or linger in transit warm up (especially during warmer harvest months). Each degree temperature increase accelerates oxidation and microbial proliferation; by the time these grapes enter fermentation tanks, they could be hours into unintended biochemistry for which a winemaker is held responsible.
Ultimately equipment size factors into this more than producers know. Small equipment creates bottlenecks whereby grapes await processing; large equipment renders monitoring accountability moot as lots can go through too quickly for adjustments. Medium-sized equipment allows for adequate processing of typical volumes with extra cushion for peak season shifts without drastic waste.
The Whole Cluster Decision
Some producers forgo destemming all together for certain lots where they ferment whole clusters to achieve desired flavor profiles. While this decision has merit, it reflects differentiated equipment, differentiated fermentation management and differentiated expectations for finished products.
Whole cluster fermentation is not just destemming to a lesser degree; it's its own unique process where stem tannins, aromas from stems and effects of carbonic maceration all contribute. Fermenting whole clusters is best done through intention based on varietal features, vineyard criteria or stylistic goals, not done because your destemmer is subpar and inefficient.
Even producers who never really venture on whole clusters have decisions to make relative to thoroughness of destemming. For example, many people believe that 95% destemming is acceptable with one or two clusters remaining for additional structure while others believe 100% is necessary for minimalist stem inclusion. The equipment chosen informs how much control they have over this variable.
Equipment Design and Maintenance
Not every machine works the same way; not every destemming unit has the same application known as aggressive paddles that can bruise fruit. Instead, more delicate roller systems are better suited for gentle treatment, however they tend to take longer. This has implications not only on efficiency but also on the condition of the must produced by fermentation.
Worn equipment creates issues that emerge gradually over time without producers recognizing them immediately. A paddle that used to efficiently remove stems now leaves more behind; a screen that used to effectively separate fragments now permits them through. These changes occur slowly enough that producers may not recognize them until hindsight comes in the form of tannin profiles.
Regular maintenance/calibration mean much more than cellars give credit. Each piece of equipment may require different adjustments based on what's come in over the vintage; settings and calibrations should be put in place before crush starts as this saves remediation work down the line.
Matching Equipment to Your Philosophy
Sometimes small producers think they can't afford destemming efforts/equipment so they end up giving up with hand-sorting and ineffective processing efforts, but these efforts work at minuscule volumes until they become problematic at larger productions. Therefore, a jump between manual processing to equipped efforts represents one of the biggest quality adjustments that is made when a winery grows.
Conversely, larger producers over-process their systems to make them huge and complex where there's overkill for people who pride themselves on hands on control and lot by lot customization. Equipment should match your production philosophy, not just your size.
What Quality Actually Costs
Quality equipment represents investment cost but poor destemming costs equity from minute one from how every bottle you produce will taste improperly due to poor destemming efforts. Tannic wine that comes across as too harsh or too green won't sell for high prices while wine with no structure or fails to age improperly will develop quality issues that hail back to where you should have processed.
Payback comes in consistency from good processing equipment. If each lot receives the appropriate crushing/destemming process then quality discrepancies decrease throughout your production.
Building A System That Works
Destemming does not exist in a vacuum as part of an overall system, from grape reception, sorting to crushing, and fermentation vessel addition, everyone aspect influences another so equipment notes must consider every single step in order.
Bottlenecking systems anywhere brings quality issues everywhere, grapes waiting in line to be destemmed start fermenting on their own time; must waiting to be pumped begins oxidizing; fermenters waiting to be filled create scheduling problems for others needing time as well. Proper systems design eliminates these waiting gaps as long as fruit can move sufficiently enough through processing quickly enough that no quality is lost but slowly enough where control is kept.
Destemming is not one decision but a compounding series of interconnected equipment, setting, timing/, and stylistic choices that compound through every successive decision-making unit. If you can get the foundation right, everything else will be easier; if you get it wrong, you'll be attempting to fix your problem well into wine production once it starts fermenting in the crushers.