CIE42 Proceedings, 16-18 July 2012, Cape Town, South Africa © 2012 CIE & SAIIE

CONCEPT INVESTIGATION OF A MOBILE VINEYARD PRESS FOR WINE GRAPES K. Lemmer1*, N.F. Treurnicht1, W. du Toit2 and J. Brand2 1 Department of Industrial Engineering Stellenbosch University, South Africa [email protected] [email protected] 2

Department of Viticulture and Oenology Stellenbosch University, South Africa [email protected] [email protected]

ABSTRACT During the ripening of wine grapes, variables beyond the control of winemakers cause harvest peaks to occur, placing high demands on primary processes in wine cellars. The result is queuing that leads to truck and tractor trailer loads of grapes waiting for unloading. The atmospheric exposure during queuing possibly causes quality degradation. This study has two objectives: Firstly, to alleviate pressure on wine cellars caused by the grape supply peak during the harvest season; Secondly, to increase the quality of the end product, namely juice or wine by minimising the time the grapes are exposed to heat and the atmosphere. In this work the concept of a mobile vineyard press is explored. Such equipment would enable immediate pressing (of white wine grapes in particular) after harvesting and the transport of chilled juice to the cellar. The study analyses harvesting processes at a sample of Lutzville vineyards. Harvest processes are investigated in order to predict typical peaks occurring at cellars. The time harvested grapes are exposed before pressing is determined, and then the extent to which the vineyard pressing influences this time. The study concludes with the presentation of a concept design for a batch vineyard press.

*

 Corresponding  Author  

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CIE42 Proceedings, 16-18 July 2012, Cape Town, South Africa © 2012 CIE & SAIIE

1

INTRODUCTION

Oxidation and the subsequent browning of either the juice or the wine is one of the most unwanted effects during wine making as it adversely affects the sensory properties of wine, namely colour, flavour and aroma and increases the astringency [11]. From the moment that grapes are picked, they begin to undergo this natural process of oxidation, whereby parts of the grape are exposed to oxygen in the atmosphere. During harvest season farmers are faced with large quantities of grapes that need to be harvested at their optimum ripeness. The grapes must then be transported and also further processed as quickly as possible to avoid oxidation, putting pressure on these farmers to accomplish a rather difficult set of tasks. “Grapes are received in a narrow window of opportunity and for quality’s sake the faster the grapes get from trucks through destemmer crushers, and in the case of white wine, through a press, the better it is for the wine and the specific winery,” [1]. Reductive treatment of juice, as opposed to oxidation thereof prior to fermentation, resulted in wines with higher aroma intensity and quality [3, 5]. Further studies by J. Marais [3] investigated the effects of grape temperature, oxidation and skin contact on Sauvignon Blanc juice and wine. It was shown that lower temperature skin contact under reductive conditions affects wine composition and quality positively. Higher temperatures during storage are closely associated with oxidative degradation of white wines [9, 10]. Increased temperature during skin contact also resulted in deeply coloured white wines and higher levels of total phenols [6]. These phenolic compounds are closely related to the browning capacity of wines, as they are highly susceptible to oxidation [7, 8, 11]. According to Pocock et al.[2] grapes that have been mechanically harvested and transported over long distances, contained more heat unstable proteins than grapes that were handpicked and held on ice. The major reason for this is believed to be the greater extraction of protein from the skins during transport of the broken berries. The effect of this increase in heat unstable proteins leads to the need to add approximately double the amount of bentonite, an adsorbing agent used to clarify the wine and prevent hazing. Transportation of grapes, especially over long distances, whether mechanically harvested or handpicked, is relatively difficult and often costly under the ideal cool conditions necessary in order to prevent oxidation and browning. This study aims at providing wine farmers and cellars with a partial solution to help alleviate the loads placed on cellars during harvest season, as well as minimizing the effects of oxidation between harvesting and further processing of the grapes/juice at the cellar, by determining the feasibility of a mobile vineyard press. Grapes can be destemmed, cooled and pressed within the vineyard, the cellars can then receive the cooled juice, eliminating the need for these processes to be done at the cellar. It is believed that if the grapes are pressed and separated from the skins as soon as possible, there will be fewer heat unstable proteins in the juice. To determine whether the mobile vineyard press will alleviate some of the load of the cellars and minimize oxidation, a time study was conducted which used Mulderbosch Wine Estate in Stellenbosch as a case study, where the flow process chart of current conventional procedures was analysed and compared to that of the mobile vineyard press. Included in this chart is the atmospheric exposure time of the grapes/juice, which is directly linked to the oxidation and browning capacity of the juice. A conclusion can then be drawn as to whether the mobile vineyard press is a feasible concept to assist famers and cellars in dealing with peak grape loads and quality issues.

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MATERIALS AND METHODS

Flow Process Chart Analysis Mulderbosch wine farm in Stellenbosch, South Africa, was used as a case study to run the time trials for the process flow chart. Mulderbosch currently buys Sauvignon Blanc grapes from Lutouw Estate situated in Lutzville, South Africa. With a distance of approximately 400km between them, this would provide an ideal opportunity to test transportation issues, as once the grapes are harvested in Lutzville, they must be transported in either open containers (if mechanically harvested), or the choice of closed cooled containers (usually for handpicked grapes) back to Mulderbosch wine farm. Two methods, namely conventional transport and pressing; and immediate vineyard pressing, are analysed and compared using a process flow chart. The chart specifically focuses on the wine grapes used, and determines for each process the following factors shown in Table 1. Table 1: Process Analysis Factors Distance Travelled

(metres)

Time

(minutes)

Exposure Time

(minutes)

Labour

(labourers needed for an 8 hour shift)

The two methods are analysed from the moment the grapes have been harvested until the juice from the pressed grapes is transferred into the container in which further processing of the juice will take place. For each process analysed, 500kg bins were used as the batch size, hence time and distance were measured per 500kg load of grapes. The mobile vineyard press process analysis was based on estimated throughputs and distances based on the proposed concept design in this paper.

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RESULTS AND DISCUSSION

This experiment was designed to determine whether the concept of a mobile vineyard press would help alleviate the load placed on cellars during harvest season, as well as minimise the effects of oxidation during processing and transportation of the grapes/juice. The flow diagrams for each method, namely the conventional method and the mobile vineyard press method, are presented in Error! Reference source not found. and Figure 2, respectively. Analysing these diagrams in more detail and conducting time trials yielded the results shown in Table 2 and Table 3. For both processes, the grapes are first harvested either mechanically, handpicked, or picked as whole-bunch (whole-bunch picking is typically used for sparkling wines). When the conventional method is used the grapes are transported to the relevant cellar. Once the cellar has received these grapes, the bins are unloaded and tipped into a large receiving hopper. For handpicked grapes, the hopper then feeds into a crusher/destemmer, through the mash cooler and into the press. Mechanically harvested grapes are fed from the hopper through the mash cooler into the press. Whole-bunch grapes are fed straight from the hopper to the press. Once these grapes have been pressed, the juice is then pumped into cooled containers for further processing. In the case of the mobile press, the harvested grapes are tipped into the hopper on the mobile system, where the handpicked grapes are then destemmed/crushed, pumped through the mash cooler and into the press. The mechanically harvested grapes are pumped from the hopper through the mash cooler and into the press, whereas the whole-bunch grapes are fed from the hopper straight to the press. These grapes are then pressed and the juice is pumped into the cooled transport tanker, and transported to the relevant cellar. Once the cellar receives the cooled juice, it is pumped into cooled containers inside the cellar for further processing.

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Mechanical

Harvesting

Harvesting

Method

Method

Handpicked

Mechanical

Whole-Bunch

Handpicked

Transport

Destmmer/ Crusher

Destemmer/ Crusher

Mash Cooler

Mash Cooler

Whole-Bunch

Press

Press

Cooled Tankers

Further Processing

Transport

Figure 1: Conventional Flow Diagram Further Processing

Figure 2: Mobile Press Flow Diagram

The distance, time, exposure time and labour for each process of the two methods is presented in Table 2 and Table 3. The distances travelled as well as the time for both methods are relatively similar. There is a major difference in the exposure times of the two methods (further emphasised in Figure 3) with the conventional method having a much higher exposure time. In terms of labour, both methods proved to be relatively similar, with the conventional methods requiring 2 more labourers in an 8 hour shift than the mobile press method.

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Table 2: Analysis of the Conventional Process Distance             Time             Exposure  Time             Labour* (m) (min) (min)

Process

Tipping  i nto  Transport  Container -­‐ Transport 400km  Offloading  of  bins 30  Tipping  i nto  hopper 2  Destemmer/Crusher 2  Mash  Pump 10  Mash  Cooler 10  Press 5  Pump 20  Cooled  Tankers 5 Total 84 * Labour  based  on  workers  needed  during  an  8  hour  shift

1

1

360

360

-­‐

1

1

2

2

2

1

2

2

0

2

0

1

2

0

0

180

0

1

2

0

0

2

0

0

554

366

6

1

Table 3: Analysis of the Mobile Press Process Distance             Time             Exposure  Time             Labour* (m) (min) (min)

Process Tipping  i nto  Hopper  Destemmer/Crusher  Mash  Pump  Mash  Cooler  Press  Pump  Cooled  Transport  Tankers Transport Total

-­‐

1

1

1

2

2

2

0

2

1

0

1

10

2

0

0

5

180

0

1

10

1

0

0 0

5

2

0

400km

360

0

1

34

549

3

4

* Labour  based  on  workers  needed  during  an  8  hour  shift

Figure 3: Handling Times of Grapes

Time  (min)  

Handling  Times   600   500   400   300   200   100   0  

Total  Time   Exposure  Time   Conven�onal   Mobile  Press   Method   Method  

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It must be noted that the exposure times during pumping and pressing were taken as negligible, as it was assumed that a reductive press was used, where no atmospheric exposure was present and pumps had minimal exposure to air. The reason for the slight difference in the distances travelled can be attributed to the extra bin offloading and tipping procedures needed for the conventional method, as well as the design of the mobile press, where the layout of equipment is more compact and hence the product is transported over shorter distances. To utilise the advantages of cooler conditions during harvest season, grapes are usually harvested during night time or early morning. Once harvested, these grapes must be transported and this usually occurs in much warmer conditions. The high exposure time for the conventional method is mainly due to the transportation of grapes. Phenolic compounds continually extracted from the skins during transport are vulnerable to oxidation and closely related to the browning of wines [11]. With the mobile press method the skins are separated from the juice prior to transportation, hence minimising the concentration of phenols in the juice. Besides the long distance transport exposure time, the conventional method has twice the amount of exposure time per 500kg bin (6min) compared to the mobile press method (3min). The reason for this is the extra bin tipping and offloading needed for the conventional method. The atmospheric exposure time of the conventional method, together with results from [3, 5, 6, 7, 8, 9, 10], suggests that the mobile cellar concept protects the quality of the grapes/juice to a much greater extent. Although the difference in labour needed is minor, it does serve as an advantage point for the mobile press concept. In terms of the load alleviation during peak harvest season, it was clear from the diagrams and analyses that the press is usually the bottleneck during the processing of the grapes. The reason for this is the fact that the press processes in batches and there is not a continuous process. Therefore the entire line must wait for the press to complete a cycle in order to continue. Press cycles are also relatively time consuming, with a 10 ton press cycle averaging around 2-3 hours. Even though the mobile press is not eliminating the cellar pressing process, it does suggest that if the pressing process were to be done elsewhere in addition to keeping the press in the cellar the load on the press in the cellar would definitely be alleviated. The cellar would then receive cooled juice from the vineyards which can be pumped directly into cooled containers for further processing, thus eliminating the need for the cellar to process these grapes through the bottleneck. The Mobile Vineyard Press A suggested mobile vineyard press concept is presented in Figure 4 and Figure 5. This design was obtained from a study [4] to determine the feasibility of a mobile vineyard press for wine farmers.

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1

2

3

5

6

Figure 4: Mobile Press Concept Design

A

B

4

Figure 5: Concept Design Back View

The position of the loading tray (1) in Figure 4 is specifically for the processing of handpicked and mechanically harvested grapes. The design allows for the loading tray to be shifted directly above the press (see Figure 6) for the pressing of whole-bunch grapes. The mobile vineyard press concept design comprises the following components, numbered according to the system used in Figure 4 and Figure 5:

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CIE42 Proceedings, 16-18 July 2012, Cape Town, South Africa © 2012 CIE & SAIIE

No.

Component:

Remarks:

1

Loading tray

Receive harvested grapes which are tipped into loading tray

2

Destemmer/Crusher

Leaves, stems, etc. removed from berries and berries crushed

3

Buffer tank

Crushed berries stored in buffer tank. means of cooling jackets.

4

Mash Cooler

Crushed berries and must is cooled by means of glycol heat exchanger.

5

Press

Reductive pneumatic membrane press.

6

Cooled Tankers

Two cooled tankers, allowing for separation of free run and press juice.

A

Cooling unit

Glycol cooling unit supplies cooling jackets and heat exchanger with cooled glycol.

B

Diesel generator

Diesel generator to power all necessary equipment.

Tank is cooled by

Figure 6: Whole Bunch Pressing Setup Grapes are loaded into the loading tray from the harvesting bins (Error! Reference source not found.). The auger feeds the grapes via the shute to the destemmer ( Figure 8). The feed from the loading tray into the destemmer is controlled manually using a motorised auger system. Crushed grape berries are pumped into the buffer tank (Figure 9). The buffer tank is cooled by means of glycol cooling jackets. This allows for the crushed grapes to be stored under suitable conditions to prevent oxidation and exposure to the atmosphere. Once the press upstream is ready for the next cycle, the crushed berries/must is pumped through the mash cooler (Figure 10) to reduce the temperature to approximately 10°C. Cooled must is pumped from the mash cooler into the press (Figure 11. The press is filled and the pressing cycle commences. Cooled juice obtained from the press is pumped either into the cooled tankers (Figure 12) or directly into a cooled transport tanker to be transported to the relevant cellar. The cooled tanker design allows for free run juice to be separated from the press juice in 2 separate tankers. Once these storage tanks are filled, 53-9

CIE42 Proceedings, 16-18 July 2012, Cape Town, South Africa © 2012 CIE & SAIIE

the juice will be transferred into a tanker which will then transport the cooled juice to the relevant cellar for further processing.

Figure 7: Loading Tray

Figure 8: Destemmer

Figure 9: Buffer Tank

Figure 10: Mash Cooler

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Figure 11: Press

Figure 12: Cooler Tankers

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CONCLUSION

White wine grapes are susceptible to oxidation when exposed to atmospheric conditions after harvesting. The oxidation and browning effects are further accelerated by increased temperatures during skin contact of the juice with the skins, caused by an increase in the concentration of phenolic compounds, which are vulnerable to oxidation, and unstable proteins in the juice. Atmospheric exposure of the grapes/juice under warm conditions should be avoided in white grapes/juice. According to the process flow charts and time studies in this paper, the conventional method of transporting grapes over relatively long distances causes increased exposure times of the grapes/juice to the atmosphere. The mobile vineyard press concept seems to minimise the time between the harvesting and the pressing of the grapes, thus separating the skins from the juice as soon as possible and limiting the concentration of phenolic compounds and unstable proteins within the juice/wine, which agrees with findings of C.S. Ough et al. [12]. By minimising the concentration of phenolic compounds and heat unstable proteins caused by these exposure times, there is an increase in the end product quality, which agrees with findings from [2, 7, 8, 9 10, 11]. The press is a batch process and hence appears as the bottleneck in the processing of the grapes after harvesting. By introducing an additional press, in this case a mobile vineyard press, the load placed on the press inside the cellar should be alleviated to an extent, together with the advantages of receiving cooled juice which has had minimal atmospheric exposure.

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REFERENCES

[1]

P Baggio. A pressing issue: throughput and the big picture. The Australian & New Zealand Grapegrower & Winemaker, p.74, June 2005.

[2]

Pocock et al.The effect of mechanical harvesting and transport of grapes, and juice oxidation, on the protein stability of wines. Australian Journal of Grape and Wine Research 4, 136-139, 1998.

[3]

J. Marais. Effect of Grape Temperature, Oxidation and Skin Contact on Sauvignon blanc Juice and Wine Composition and Wine Quality. South African Journal of Enology and Viticulture 19, no.1, 1998

[4]

K. Lemmer. Concept Investigation of a Mobile Vineyard Press for Wine Grapes. MSc Thesis, Stellenbosch University, 2012

[5]

D. Ramey et al. Effects of Skin Contact Temperature on Chardonnay Must and Wine Composition. American Journal of Enology and Viticulture 37, no.2, 1986.

[6]

Singleton et al. White table wine quality and polyphenol composition as affected by must SO2 content and pomace contact time. American Journal of Enology and Viticulture 31, 14-20, 1980.

[7]

Singelton et al. Composition and sensory qualities of wines prepared from white grapes by fermentation with and without grape solids. American Journal of Enology and Viticulture 26, 62-69, 1975.

[8]

Antonio Ceäsar Silva Ferreira et al. Identification of Key Odorants Related to the Typical Aroma of Oxidation-Spoiled White Wines. Journal of Agricultural and Food Chemistry 51, 1377-1381, 2003.

[9]

R.F. Simpson. Factors affecting the oxidative browning of white wine. Vitis 21, 233239, 1982.

[10]

Nikolay Stoyanov et al. Extractability of Grape Seed and Skin Phenolic Compounds During Grape Maturity. Department of Winemaking and Brewing, University of Food Technologies, Plovdiv, Bulgaria, 2002

[11]

Hua Li et al.Mechanisms of oxidative browning of wine. Food Chemistry 108, 1-13, 2008

[12]

C.S. Ough et al. Simulated Mechanicla Harvest and Gondola Transport. II. Effect of Temperature, Atmosphere and Skin Contact on Chemical and Sensory Qualities of White Wines. Department of Viticulture and Enology, University of California, 1971.

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