WSET Diploma D1 Cheatsheet: Wine Production

D1 is the mechanism unit. Marks come from explaining why an option was chosen and what it cost, not from naming the option, so every table below pairs a decision with the effect it produces and the trade off that comes with it. Use it alongside the D1 mock test and the rest of the Diploma unit hub; if the underlying vocabulary is shaky, the Level 3 cheat sheet is the faster place to start.

The Vineyard: Soil, Water, and Climate Metrics

Soil matters through four levers, and an answer that names a soil without naming the lever earns nothing: water holding capacity (texture, depth, organic matter), drainage, nutrient supply and cation exchange capacity, and thermal behavior (dark or stony soils absorb and re radiate heat, pale soils reflect light into the canopy). Soil pH adds a fifth constraint, since high active lime blocks iron uptake and causes chlorosis, which is a rootstock decision rather than a fertilizer one.

Vine water status, not rainfall, is what shapes the wine. Mild deficit after fruit set restricts cell expansion, so berries stay small, the skin to juice ratio rises, and anthocyanins, tannins, and flavor compounds concentrate; the vine signals that deficit through abscisic acid, which slows shoot growth and moves assimilates toward the bunches. Severe deficit closes stomata, halts photosynthesis, and strands the fruit unripe. Growers measure vine water potential with a pressure chamber rather than reading the soil, and manage it through regulated deficit irrigation, partial rootzone drying, cover crops, mulching, or rootstock choice.

Vine Physiology and Phenology

The vine’s yearly cycle is a sequence of risk windows, and each one has a distinct failure mode. Bud fruitfulness for next year is set during this year’s growing season, so a shaded or stressed canopy costs two vintages, not one.

Vineyard Hazards, Pests, and Disease

Frost comes in two forms and the response differs: radiation frost on still, clear nights can be fought with wind machines, helicopters, sprinklers, or heaters because there is warmer air aloft to mix down, whereas advective frost carried in on a cold air mass defeats all of them. Hail is insurable, not preventable at scale. Sunburn is a canopy question. Smoke taint is a chemistry question, because the volatile phenols bind to sugars as glycosides that survive fermentation and hydrolyze later, so a wine can taste clean at bottling and taste of ash a year on.

Rootstocks and Phylloxera

Phylloxera is native to eastern North America and reached Europe in the second half of the nineteenth century, where it destroyed vineyards on a scale that reset the industry: it feeds on the roots of Vitis vinifera, which has no resistance, and the durable answer was grafting vinifera scions onto American species roots. Chile has never had it, and it does not establish in pure sand, which is why ungrafted vines survive at Colares and on Santorini. Rootstock choice is now a site engineering decision, not just a phylloxera insurance policy.

Canopy Management, Trellising, and Yield

Vine balance is the goal, expressed as the ratio of leaf area to crop weight, or in the field as the ratio of harvested crop to winter pruning weight. Too much vegetative growth and the shoot tips outcompete the bunches for assimilates while the canopy shades the fruit; too little and the vine cannot ripen what it carries. High vigor sites are fixed by devigoration (cover crops, lower vigor rootstock, no irrigation) or by dividing the canopy, not by hedging harder, since summer topping simply provokes laterals.

Yield is controlled most reliably at pruning, because the bud count fixes the potential crop before the vine spends anything on it. A green harvest at veraison is a corrective tool: the vine can compensate by swelling the berries left behind, which partly cancels the intended concentration. Appellation yield ceilings in hectoliters per hectare are a legal constraint, not a quality guarantee, and low yield only helps up to the point where vine balance breaks.

Harvest date is the last viticultural decision and the first winemaking one. Sugar (measured as Brix, Baume, or Oechsle), total acidity, and pH are the numbers; tannin ripeness, seed color, skin extractability, aroma precursors, and the state of any botrytis are the judgments. Hand picking allows selection, whole bunches, and successive passes; machine picking is faster and can work at night, which preserves aromatics, but it delivers detached berries with juice already flowing, which rules out whole bunch pressing and carbonic maceration.

The Winery Before Fermentation

Fruit arrives warm, oxidizing, and full of decisions. Chilling on reception, inert gas, dry ice, and an early sulfur dioxide addition protect aroma; hyperoxidation does the opposite on purpose, deliberately oxidizing a white must so the oxidizable phenols polymerize and drop out, leaving a wine that is more stable later. Sorting runs from a vibrating table through optical sorters that reject by color, size, and shape, to density sorting in a flotation bath.

Must adjustments are legally constrained and regionally revealing. Enrichment (chaptalization with sucrose or with rectified concentrated grape must) raises potential alcohol in cool regions and is banned in warm ones; acidification with tartaric acid is standard in warm regions and restricted in cool ones. Tartaric is chosen because it is the strongest grape acid and, unlike malic acid (converted during malolactic conversion) or citric acid (metabolized by lactic acid bacteria into acetic acid and diacetyl), it is not consumed by wine microbes. Deacidification uses calcium carbonate or potassium bicarbonate. Pectolytic enzymes aid settling, extraction, and pressing yield.

Whole bunch pressing of white grapes gives the lowest phenolic must of all, because the stems act as drainage channels through the mass of fruit, so the juice runs off quickly at low pressure with minimal skin contact. The costs are press capacity and cycle time.

Fermentation

Alcoholic fermentation runs through glycolysis: glucose to pyruvate, pyruvate decarboxylated to acetaldehyde, acetaldehyde reduced to ethanol by alcohol dehydrogenase, with carbon dioxide, glycerol, and a great deal of heat as the other outputs. Knowing the acetaldehyde step explains why a struggling ferment smells of bruised apple and why acetaldehyde later binds so much of the sulfur dioxide added to the wine.

Yeast choice is a risk decision. Cultured Saccharomyces cerevisiae strains are selected for alcohol and temperature tolerance, low hydrogen sulfide production, thiol release, or foam behavior, and give a fast, reproducible ferment. An ambient ferment runs as a succession, with non Saccharomyces genera dominating the early phase and adding aromatic complexity and glycerol before Saccharomyces takes over; the price is slower, less predictable kinetics and greater exposure to volatile acidity and stuck fermentation.

Nutrition is the other half of that question. Yeast assimilable nitrogen (ammonium plus free amino nitrogen) drives cell population and fermentation rate: too little gives sluggish ferments and hydrogen sulfide, too much gives a violent ferment, excess heat, fusel alcohols, and elevated volatile acidity. Diammonium phosphate is the fast correction and organic nitrogen preparations the gentler one, both best split across the ferment. Yeast also need a little oxygen early for sterol synthesis, which is why an aerative pump over in the first days is protective rather than damaging.

Stuck fermentation is a Diploma favorite because the causes are diagnostic: nitrogen deficiency, temperature too high or too low, very high initial sugar, excessive alcohol, toxic medium chain fatty acids, low oxygen early, competition or killer factor from wild flora, or an SO2 addition at the wrong moment. Restarting means acclimatizing a robust restart culture into a small volume, adding nutrients, adjusting temperature, and blending the stuck wine in progressively. The real danger is not the delay but the window it opens for acetic acid bacteria and Brettanomyces in a wine with residual sugar and a shrinking sulfur dioxide reserve.

Red Winemaking and Extraction

Anthocyanins are water soluble and come out early; tannins are more alcohol soluble and extract as the ferment progresses, with seed tannin arriving late and harsh. That is the whole logic of extraction management: extract color early and gently, decide how much seed tannin to accept, and then let time in contact with alcohol polymerize what you have taken into softer, more stable pigment tannin complexes.

Malolactic Conversion

Oenococcus oeni converts sharp diprotic L-malic acid into softer monoprotic L-lactic acid, releasing carbon dioxide. Titratable acidity falls, pH typically rises by around 0.1 to 0.3, texture softens, and the wine gains microbial stability because the malic acid that a stray bacterium might have fermented in bottle has already gone. Diacetyl, the buttery compound, is an intermediate: how much survives depends on the strain, on oxygen, on lees contact (yeast metabolize diacetyl back down), and on when SO2 is added.

Encouraging it means warmth in the region of 18 to 22 degrees Celsius, low free SO2, lees contact, and usually inoculation. Blocking it, which is the choice for aromatic whites and for many cool climate sparkling base wines, means free SO2, chilling, racking off the gross lees early to remove the bacterial population, lysozyme, and a sterile filtration before bottling. The risks of an uncontrolled conversion are volatile acidity, biogenic amines, ropiness, and mousiness, particularly at higher pH.

Maturation

Lees are the second lever. Gross lees carry solids and can turn reductive; fine lees, kept deliberately, consume oxygen and release mannoproteins during autolysis, adding palate weight, binding harsh tannin, and improving protein and tartrate stability, which reduces the bentonite and cold treatment needed later. Batonnage suspends them, accelerating the effect and introducing a little oxygen.

Oxygen management runs through everything. Topping up (ouillage), racking frequency, headspace inert gas, vessel choice, and the number of pump transfers together set a cumulative exposure that either polymerizes tannin, stabilizes color through ethyl bridged pigments, and builds complexity, or tips into oxidation. Micro oxygenation applies the same principle in tank at a controlled dose per liter per month; developed for very tannic reds, it softens texture and fixes color, but over dosing invites oxidation and hands Brettanomyces the conditions it likes.

Stabilization, Fining, and Filtration

Three instabilities are worth separating. Tartrate instability is cosmetic: potassium bitartrate crystals form in a cold bottle and consumers mistake them for glass. It is treated by cold stabilization near freezing, by the contact process seeded with cream of tartar, by electrodialysis or ion exchange, or by inhibitors such as metatartaric acid (temporary), carboxymethylcellulose (which requires a protein stable wine first), and mannoproteins. Protein instability is a white and rose problem, diagnosed with a heat test and fixed with bentonite. Microbial instability is the dangerous one, handled with molecular SO2, sterile filtration, sorbate plus SO2 in sweet wines, or dimethyl dicarbonate at bottling.

Filtration is either depth (diatomaceous earth, sheets), which traps particles within a matrix, or surface (membrane cartridges, cross flow), which excludes by pore size. A sterile membrane filtration removes yeast and bacteria and is the only reliable way to bottle a wine with residual sugar without sorbate. The argument against heavy filtration is loss of colloids and texture, which is why many fine red producers bottle unfined and unfiltered and accept the sediment.

Sulfur Dioxide Chemistry

Total SO2 is free plus bound. Bound SO2 is combined with acetaldehyde, pyruvic acid, ketoglutaric acid, anthocyanins, and sugars, and it is largely inert. Free SO2 sits in a pH dependent equilibrium between molecular SO2, the bisulfite ion, and sulfite; only the molecular fraction is meaningfully antimicrobial, and it is also the fraction that scavenges the hydrogen peroxide and quinones produced when phenols oxidize. The practical target for microbial protection is commonly around 0.8 mg/L molecular SO2, and what that costs in free SO2 depends entirely on pH.

That table explains a large part of D1. A high pH red is microbiologically fragile because the SO2 addition needed to protect it approaches the legal ceiling and the sensory threshold at the same time. EU limits sit at 150 mg/L total for dry red and 200 mg/L for dry white and rose, with higher ceilings for sweet wines and lower ones under organic certification. SO2 also inhibits the grape’s own polyphenol oxidase, though laccase from botrytis affected fruit is far more resistant, which is why heating the must is used on rotten fruit.

Packaging and Closures

The bottling line is where a year of careful oxygen management is most easily undone. What matters is total package oxygen: dissolved oxygen picked up during filtration and filling, plus the oxygen trapped in the headspace, plus whatever the closure transmits over time. Green or amber glass protects against light strike, in which riboflavin drives the degradation of methionine into foul smelling sulfur compounds; clear glass under retail lighting does not.

Alternative formats trade shelf life for carbon footprint and convenience. Bag in box and kegs remove headspace oxygen entirely but have limited life once the barrier film is breached; cans require an internal liner, because aluminum in contact with wine at low pH can generate hydrogen sulfide, and both SO2 and chloride levels have to be managed carefully.

Wine Faults

Study This With Sommo

Tables get you recall; D1 is graded on explanation. Sommo turns this page into spaced repetition flashcards and typed answer drills that grade the mechanism you wrote, not the keyword you remembered, so you find out which chains you can actually explain before an examiner does. Try the full Diploma mock test next, then download Sommo free and keep the vineyard and winery material warm between study blocks.