VEN124 Section II Grape and Must Processing

Lecture 4: Grape Processing

Reading Assignment: Text, Chapter 3, pages 65-79;

In this lecture we will cover the processing steps of crushing/destemming and pressing. The lecture will include a detailed discussion of the issues to be considered when purchasing a crusher/ destemmer

Definition We generally refer to “must” as the material that contains juice, skins and seeds and reserve the term “juice” for the material pressed off of skins and seeds.

Grape Processing: Crushing/Destemming

To Crush or Not Crush? A Matter of Style

Crushing/Destemming Purpose Stylistic Options Equipment Choices

Purpose of Crushing Better extraction of juice Better maceration of skins Opportunity to remove stems

Crushing: Stylistic Options No crushing –Direct to Press –Whole Berry Fermentation –Carbonic Maceration Crushing –Temperature –Percentage of Intact Berries

Direct to Press Minimizes extraction from skins Used for white and blush wines Used to reduce/manipulate varietal character May be used for cryoextraction/ cyroconcentration

Whole Berry Fermentation Clusters are suspended in juice/ethanol Slower fermentation Retains fruit characteristics Juice

Carbonic Maceration Juice CO 2 Atmosphere Vessel Sealed

Carbonic Maceration Berries asphyxiate Lose some characters due to continued berry enzymatic activity No ethanol extraction but ethanol is produced by fruit Develop characteristic flavors of silage and strawberry Wines do not age well

Whole Berry Fermentation vs. Carbonic Maceration In whole berry fermentation the ethanol produced by yeast penetrates berry inhibiting “decay” reactions seen with carbonic maceration Presence of whole berries during most active phase of fermentation traps volatile aroma characters and prevents loss due to CO 2 entrainment, increasing the varietal character of the finished wine

Whole Berry Fermentation vs. Carbonic Maceration In carbonic maceration, the slow process of asphyxiation of the fruit leads to loss of varietal character and the appearance of new characters due to both loss of masking as well as de novo synthesis

Cryoextraction/Cryoconcentration Use principle behind ice wine production Freeze grapes to remove water as ice Freeze grapes to damage skins and improve extraction Grapes must be processed at low (below 0°C)

Location of Crushing Operation In the field – as fruit is being mechanically harvested At winery – raises issues of delivery of undamaged fruit

Types of Crushers Crusher/Stemmer –Separates stems from crushed fruit –Desirable when: Stems impart a negative or undesired character to wine Early stem removal facilitates downstream processing Crusher/Stem Disintegrator –Breaks up stems along with fruit –Desirable when: Stems impart positive character Stems increase yield upon pressing

Crushing: Choice of Equipment We will now consider the factors that should be considered when choosing a crusher/destemmer to purchase

Choice of Crusher Ease of Inspection/Cleaning –Microbial populations build up on crusher: want little to no juice “reservoirs” –Source of inoculation of entire production –Ease of taking apart/putting back together

Choice of Crusher Ease of Inspection/Cleaning Qualities of Must

Hole size: amount of berry damage Hole surface (smooth or rough?): amount of berry damage Type of paddle: plastic might not hold up like stainless steel Clearance between basket surface and paddles: amount of shearing

Qualities of Must (continued) Rollers: Adjustable? Can they be bypassed? What % breakage of berries do you want and can crusher deliver that reproducibly? How much clearance of stems do you want and can crusher deliver that reproducibly?

Choice of Crusher Ease of Inspection/Cleaning Qualities of Must Rate of Feed vs. Capacity of Winery

Is crushing rate-limiting? –Slow press/tank fill allows: Oxygen exposure Growth of aerobes Loss of volatiles Slows processing of harvest Is flow rate from crusher too fast? –Heat from friction –Over shoot tank

Choice of Crusher Ease of Inspection/Cleaning Qualities of Must Rate of Feed vs. Capacity of Winery Dependability –Breakdown frequency –Ease of mechanics/repair –Type of materials/construction

Choice of Crusher Ease of Inspection/Cleaning Qualities of Must Rate of Feed vs. Capacity of Winery Dependability Overbuilt?

Will be running at sub-optimal conditions May not meet specifications/expectations Increases chances of equipment failure If remove berries in first third of crusher then the rest of the time the stems are simply being whacked about which will result in the appearance of stem fragments in the must

Choice of Crusher Ease of Inspection/Cleaning Qualities of Must Rate of Feed vs. Capacity of Winery Dependability Overbuilt? Compatibility with Other Equipment

Using auger, conveyer belt, forklift or hand delivery of fruit to crusher? How key is uniformity of feed for optimal performance of crusher? Capacity of must pump

Choice of Crusher Ease of Inspection/Cleaning Qualities of Must Rate of Feed vs. Capacity of Winery Dependability Overbuilt? Compatibility with Other Equipment Is Adjustment Possible While Running?

Adjustment While Running Allows for adjustment of must quality without stopping and restarting operation –Berry loss with stems –Seeds being crushed –Stems cracked Allows for non-uniform juice composition which may increase desirability of final product

Choice of Crusher Ease of Inspection/Cleaning Qualities of Must Rate of Feed vs. Capacity of Winery Dependability Overbuilt? Compatibility with Other Equipment Is Adjustment Possible While Running? Service

Spare parts accessibility Availability of service personnel –Technical expert vs. salesperson Speed of response Cost Operating manual clearly written –Wiring diagram –Trouble shooting guide

Choice of Crusher Ease of Inspection/Cleaning Qualities of Must Rate of Feed vs. Capacity of Winery Dependability Overbuilt? Compatibility with Other Equipment Is Adjustment Possible While Running? Service Portability

Can Crusher/Destemmer be moved? How well can it be leveled? How sturdy is it?

Grape Processing: De-juicing

In some cases, it may be desirable to separate the juice from the skins and seeds using a de-juicing tank. This process can occur prior to pressing in white and blush wine production to yield a juice with minimal extraction.

De-juicer tanks Skins and Juice Juice

De-juicing Once de-juicing is complete, the tank is then moved over the press and the must dumped into the press. Continuous de-juicers based on must traveling over a screen are also available.

Grape Processing: Pressing

Purpose Stylistic Considerations Equipment Options

Purpose of Pressing To recover juice/wine associated with pulp, skins and seeds that would not be released by simple draining Can separate press fractions to manipulate juice/wine composition

To Press or Not Press? A Matter of Timing.

Timing of the Pressing Operation Maceration/Skin Contact first: To allow greater extraction of materials from skins prior to removal by pressing Fermentation first: To enhance extraction by ethanol, CO 2, and heat of fermentation Stylistic reasons for late pressing: Whole Berry Fermentation Carbonic Maceration

Pressing: Equipment Options Batch Basket Press Cylindrical Press Continuous Screw Press Belt Press

Basket Press Ideal for small volumes Low yields/High volume loss Low damage to seeds and skins (minimize extraction) Uniform pressure difficult Messy to clean

Basket Press Piston Juice

Cylindrical Presses Piston Air Bladder Vacuum Easy to control pressure uniformly Elaborate pressing cycles and separation of juice lots possible Moderate yield Somewhat messy to clean

Cylindrical Presses Piston Juice Air Bladder

Vacuum Presses Apply vacuum to extract liquid Compatible with very low temperatures

Screw Press High yield High tissue (seed and skin) damage High solids content of juice Higher astringency of wines

Dry Pomace Wine/Juice Screw Press

Belt Presses Juice can be drained at different levels of pressure Low to moderate to high yield: fully adjustable May break seeds due to shear forces Microbial population build up can be a problem

Belt Press Juice can be removed at different pressures Dry Pomace

Choice of Press Yield vs. Quality Affects juice composition: phenolics, tannins, pH Stylistic considerations Cost

Pressing Aids Inert material that can be used as a hard surface against which to press must Increases yield of juice