In Part One of our guide to building a crush pad we looked at receiving and processing grapes for fermentation or pressing. Let's now take a look at presses.

The question of basket vs. membrane press comes up frequently, so let's address it upfront.

Basket vs. Pneumatic Membrane Presses

Since we're focusing on crush pads processing anywhere from 3 to 20+ tons per hour of grapes, we'll look at the two most popular options for crush pads of this size: basket and pneumatic membrane presses.

Basket Presses

For a deeper dive you can check out our Guide to Basket Presses. But as a general overview, basket presses have a "platen" (large flat plate) that is connected to one or more hydraulic pistons. The pistons push the platen down slowly until it reaches the grapes held in a cylindrical basket. These hydraulic pistons are capable of generating tens of thousands of pounds of force. As this force reaches the grapes and is distributed over the surface of the grapes, juice runs through the grapes and out the sides of the basket. It collects in a tray that holds the basket. The pressed-out juice is then transferred on to storage or fermentation tanks. The user removes the pressed-out "cake" from the basket, and a new load of grapes can be prepared for pressing.

Membrane Press

Pneumatic membrane presses look a bit like a big stainless tank lying on its side, and that's essentially what they are.

You load a membrane press through doors in the rotating drum. Once the drum is filled, the user shuts the door and begins a pressing cycle. These automated cycles involve alternately rotating the drum and inflating the membrane inside with compressed air. This inflate/rotate cycle is repeated a set number of times. When the cycle is complete, the pressed-out cake can be dumped from the drum, and the press can be reloaded with more grapes.

What is each press style best for?

To paint with broad strokes, basket presses are best at pressing fermented red grapes, while bladder presses are best for fresh and whole cluster grapes. This doesn't mean you can't do fermented reds in a bladder press, or whole cluster in a basket press. You certainly can, but the results will differ.

If a winery has both a membrane press and a basket press, they will typically use the basket press for their high-end red grapes. This is because basket presses are very gentle. Remember, the grapes in a basket press are static. They don't move around. This means they're extremely gentle, which is critical for processing delicate fruit without resulting in a lot of lees.

The main downside of basket presses relative to membrane presses is their size limitation. The largest available basket press tops out at around 15-20 HL or so. Meanwhile the largest membrane presses may be as large as 150 HL; so about 10x as big.

While pneumatic bladder presses can also be used to press fermented red must, they may not be the first choice for this task. The repeated cycle of press, rotate, press, rotate tends to break up fermented red that is already quite delicate. This leads to juice with higher lees content that requires more processing than juice from a basket press.

On the other hand, membrane presses are an excellent choice for fresh destemmed grapes. Since they can run through preprogrammed cycles of pressing & rotating to break up hard packed cake, they are able to extract juice from fresh grapes more easily than basket presses where the cake remains static and pockets of unpressed grapes may form.

If you want to get a basket press and use it for both fresh and fermented grapes, there are a few tactics to help. One such tactic is to use extra nylon diaphragms to break up the layers and keep pockets of unpressed grapes from forming. Whereas with a typical load of fermented red must you would normally use three diaphragms to break up layers, with a load of fresh grapes you may need to use 6-9 diaphragms. This keeps the distribution of grape layers more consistent.

What Size Press Should I Get?

If you want some clarification about press size terminology, we address different ways to think about it in this article.

Once you have the basics of sizing terminology well in hand, you should consider how many tons you will be processing in total and per hour. Given that press cycles may take about 1–2 hours including loading/unloading, try to determine how many pressing cycles you would like to run in a given day to arrive at the best size.

Also bear in mind the smallest load you anticipate pressing. Mori's basket presses can reach to within about a foot of the bottom, so the minimum load may be as small as about 1/4 of the basket.

Membrane presses, on the other hand, should not be under-loaded or you risk damaging the membrane. The minimum load should be no smaller than about 1/3 the basket, and you must lower the maximum pressing pressure to compensate for smaller loads.

In summary, try to understand how many tons you'll be processing per hour, how many pressing cycles you can accommodate per day with your available crew, and what your minimum load is likely to be. This should help you narrow in on the right press size for your facility.

Side Note: Maximizing Throughput

To get a bit of extra throughput with a basket press, some of our customers buy an additional tray or basket/tray combo. Here's how it works with a Mori PZ press. While one load is pressing, you can start filling your second tray/basket with grapes. That way as soon as you're done, you can just pull out the first basket and put the second underneath. Then you can empty and clean the first basket while pressing the second one. Load it up with another batch of grapes, and you can dramatically increase your throughput.

This strategy doesn't work with pneumatic membrane presses, of course. With those you just have to process batches in series and account for load/unload times between cycles.

How Do I Load the Press With Grapes?

It will be important to plan out how you plan to load the press. There are a number of strategies we see commonly used:

Grape Elevator

If you already have a grape elevator you can use it to load your press as well. You'll want to make sure it has adequate clearance to reach the press inlet, of course. Pneumatic membrane presses, particularly ones with leg extensions to allow dumping into bins, may have fairly high inlet doors.

There is, of course, the question of how you get grapes into the elevator, so take that into consideration. If your forklift has a bin dumper, and your elevator has an oversized inlet hopper for receiving dumped bins, this should be pretty easy. It will also save you from needing to buy a hopper that attaches to your press to receive dumped bins.

You may be able to position the the elevator so that you can empty must from your manway into the inlet of the elevator, which carries the grapes into the basket. You'll want to check all clearances first, of course.

Must Pump

The most versatile solution is a must pump. We cover different types of must pump in our Must Pump Guide.

For white grapes going direct to the press after destemming, you can simply output your destemmer into a must pump hopper. Then just pump the grapes directly into the press. Here's a picture from the previous article in this series that shows what this would look like.

To load fermented red into your pump there are a few strategies. You can move the hopper of your must pump directly underneath the manway door of your fermenter. Pump out the free-run juice until the remaining must is mostly dry. Then open the manway door so that the must can fall freely into the pump's hopper. You can reach into your fermenter with a rake or hoe through the manway and pull out any remaining must into the must pump's hopper.

We've also seen some customers use a second liquid-only pump to re-pump free run juice into their fermenter and quickly sluice out the must. You need a good-sized must pump to achieve this, but it can make short work of emptying fermenters.

Bin Dumping Hopper

Most presses have openings that are narrower than a macro bin. Therefore to load bins by forklift you will need an oversized bin dumping hopper that acts as a funnel. Otherwise you'll end up with grapes everywhere.

Bin dumping hoppers are a common add-on feature for pneumatic membrane presses. It's not as common for basket presses, but they can be made.

Conclusion

To summarize, keep in mind the following things when selecting a press:

  • Are you mainly pressing fermented or fresh grapes?
  • If pressing both fresh and fermented, can you budget for both press styles?
  • What are the smallest and largest loads you anticipate per pressing cycle?
  • How do you plan to load the press?

With a solid grasp of these fundamental questions you should have a good intuition for which style of press you need. If you have selected the press and all the gear from part one of this series, the major parts of your crush pad should be complete. We'll go over the ancillary tools you'll need during harvest in the final article in this series.

If you're struggling with these questions feel free to give us a call and talk through it with us!