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Whilst there’s been a tendency away from filtration in recent years in line with the growth in low intervention winemaking and a belief among some winemakers that the process has a sensory impact on wine, it’s impossible to avoid once you start producing no and low alcohol (NOLO) wine. The sensory attributes of NOLO winehave been the main focus of discussions and research around these products, and rightly so if you want them accepted in the marketplace. The less glamorous aspects are the consequences of removing the alcohol on the microbial stability of the wine after bottling.
“A lot of people overlook the fact that ethanol is a significant inhibitor of microbial growth and once you remove that, then you’re simply opening the gates for things to grow,” says Paul Bowyer, group oenologist for Australian filtration specialist BHF Technologies.
Whilst sulfur dioxide is an effective antimicrobial agent, its use is more and more being questioned by consumers. Sterile filtration prior to bottling is the obvious solution.
“Wine isn’t sterile unless you put it through an integrity-test sterile membrane, or pasteurise it through heat or chemical application,” Bowyer states, stressing that many winemakers are under the false impression that crossflow filtration is a sterile process.
“Most crossflows operate at 0.2 microns but it’s not a sterile process because those membranes cannot be physically tested for integrity to ensure there are no holes or ruptures that will affect its sanitising ability. Crossflow units themselves also typically cannot be heat sanitised. But a lot of winemakers have seen that their crossflow units have a nominal pore diameter of 0.2 microns and think that’s going to give them sterile wine out the other side. It’s not a sterile process and you can’t rely on it to deliver a sterile product. I’ve seen many people pigeonhole crossflows as a magic bullet and they’re not that at all, although they are an excellent cellar tool..”
Bowyer says it is also important to remember that the colloidal structure of wine changes when you remove the alcohol which can impact the filterability of a wine, and that’s before you factor in the effect of any wine additives used to counter that loss of ethanol.
He explains that there are two types of colloids: macro molecular colloids and association colloids, the latter being formed when molecules aggregate.“Macro molecular colloids are things like CMC (carboxymethycellulose), gum arabic and mannoproteins. They don’t tend to be too much of a problem when it comes to filtration by and large. We seem to see much more of a problem with association colloids, such as a proteintannin association. If you concentrate a wine, which is basically what happens when you remove the ethanol because you take out a certain portion of the volume of the wine, you’re forcing all the components of that wine into a tighter, more polar environment and that’s going to potentially change the colloidal structure of the wine which can affect its filterability.
“Crossflow filtration will disrupt those colloidal associations too, and they can reform over time, which can be anywhere from hours to months after filtration; they’re unpredictable. And when they reform they won’t reform in necessarily the same way and the filterability of that wine could be a lot worse.
“So there are two aspects to removing alcohol from wine: the micro level and the colloidal interaction that’s caused by concentrating the wine and removing that ethanol. Then there’s an extra layer if you’ve added a bunch of stuff to the wine like mannoproteins and tannins to try and replace the sensory effect of ethanol, and that can make a wine more soupy; you’ve potentially exacerbated the problem,” Bowyer cautions.
“Wine adjuncts tend to be things like yeast mannoproteins, which build up palate weight and a little bit of viscosity. Tannins also play a role in fleshing the palate out along with polysaccharidetype products, gums and all sorts of things that are contributors to palate weight and mouthfeel and can replace some of those elements that have been removed with the ethanol.”
Reducing microbial spoilage risk
To reduce the risk of microbial spoilage, Bowyer says it’s important for NOLO producers to keep the window between alcohol removal and putting the wine through sterile filtration as short as possible.
He also recommends that the products be stored in tank at lower temperatures than their alcoholic counterparts to inhibit the growth of micro-organisims. Injecting dimethyl decarbonate (DMDC) into wine at packaging is also a possibility, but Bowyer cautions that not all export markets will accept wine made using DMDC.
“The other thing I would suggest is not to use a 0.45 micron membrane as the final filter,” he continues. “I recommend switching to 0.2 microns because that’s what is used for bottled water and bottled water obviously doesn’t have ethanol in it, so it doesn’t benefit from the anti-microbial effect of ethanol either.”
Bowyer says some NOLO winemakers may like to consider pasteurisation to destroy micro-organisms, but acknowledges the process can alter the flavour profile of a wine.Associate Professor Paul Grbin is head winemaker at the University of Adelaide and represents one of the three partners, the others being The Australian Wine Research Institute and the South Australian Department of Primary Industries, who are managing a recently-established NOLO trial-scale research facility housed at the university. The aim of the facility is to develop methods and processes that will result in better NOLO wine products.
Grbin says the researchers and producers developing new products who use the facility will be encouraged to sterile filter.
“We’re definitely recommending that it has to happen. Lots of people don’t sterile filter. Most larger commercial companies do, but smaller producers tend not to sterile filter because they don’t have the capabilities to do that.
“We’re also looking at using Velcorin [DMDC] which is a cold sterilising agent as an extra string in the bow,” Grbin adds.” It’s all very nice to think about making wines without alcohol, because there are consumers who want that. But you also have to make a product that’s going to have shelf life. And they’re often sitting in supermarkets, not in nice cellars. Microbial stability is nothing that the majority of wineries can’t deal with, except for the very small. If you don’t sterile filter, then your wines are vulnerable, particularly if you’re adding sugar back in the form of grape juice concentrate and/or xanthan gum, as is the standard approach to replacing the mouthfeel lost through ethanol removal.”Wes Pearson is a research scientist at The Australian Wine Research Institute, one of the other parties in the NOLO trial-scale research facility at the University of Adelaide, and is part of the team behind a Wine Australia-funded research project that is looking at ways to optimise flavour retention in NOLO wines and find solutions to replicate the mouthfeel and texture lost when alcohol is removed.
Pearson says most of the products currently added to NOLO wine are already being used by industry to make regular wines.
“It’s not like we’ve completely delved into food products like thickeners and emulsifiers that generally get added to all kinds of foods from a textual perspective — that hasn’t really happened in wine yet. As our work goes on with these wines we’ll be pushed into new directions. We might explore products we’ve never even considered.”
Pearson continues: “The elephant in the room with no-alcohol wines is that replacing the sensory effect of ethanol is very difficult. When we do start to evaluate potential solutions, the filterability of the product is likely going to be affected. It’s a very complex puzzle.” He says a solution that would address both the microbiological stability of a wine and its filterability might be a product like DMDC that could be added to NOLO wine post-filtering.
“You treat the wine normally then, once it’s sterile filtered in the winery, you make your adds. I could see how that might be a direction that you could go down. That’s another thing that we’re looking at: what can we add to achieve microbiological stability.”
For now, Pearson says he’s not aware of any NOLO producers who have experienced issues with microbial stability using conventional methods.
“In chatting with winemakers, generally speaking, nobody’s had a disastrous outcome with a commercial product, like refermentation. So, for those winemakers, the processes that are in place currently are doing their job, they’re working. But, they also understand the risk involved in making a NOLO product. And so their approach to make them is pretty conservative when it comes to trying new things and understandably so — the risk of damage to their brand is huge.
“That’s where we’re trying to step in and wrap our heads around the potential alternatives so we can confidently say, you can add this to your wine and it’s going to achieve a certain result every time.”
Adelaide Hills-based Sidewood Estate falls into the category of Australian wineries that Pearson talks about that has turned its hand to making NOLO wines using conventional methods and is yet to experience any major disasters.
Sidewood Estate released two no-alcohol products in 2022 — a sparkling and a Sauvignon Blanc under a label it has called Nearly Naked. The winery uses a spinning cone column at Australian Vintage Limited (AVL) to remove the alcohol from these wines.
“We send it (to AVL) as a finished, crossflowed, bottle ready wine,” explains Sidewood’s chief winemaking consultant Darryl Catlin. “It comes back not that much altered in terms of colour, NTUs and all that sort of stuff — it’s pretty well all the same.
“When it comes back, it’s all about maintaining low temperatures, sulfur levels, and making sure that it is crossflow filtered again just to make sure that if it did pick up anything we reduce those colloidal-forming components and any kind of thing that can start to grow again. It’s also about maintaining that inert gas cover and low DOs — those kind of things that we normally do anyway at the bottling line.
“In some cases, if we’ve got pressure tanks available, we might even keep the wine in them under a little bit of positive gas pressure, that kind of stuff. But, mainly, it just maintained at cold temperatures in other tanks.
“You just have make sure that as soon as you add sugar in any form or concentrate, you need to be able to bottle it straightaway, don’t hesitate. That hesitation or a breakdown in the bottling line will mean you’ll struggle to hold it from refermenting, unless you flash pasteurise or something like that, but then you might affect the quality,” Catlin advises.
“We probably do have some filterability issues somewhere, but we haven’t experienced any major problems at the stage. Once we run it through our crossflow it seems to go through our pre-bottling filters OK. But, we probably need to do a couple more bottlings to really get some evidence.”
Catlin says Sidewood Estate’s winemaking team did a lot of research before it embarked on producing a 0% alcohol product, and finding data on sterile filtration as it relates to the production of such products was the hardest to come by.
“We normally bottle under the 0.45 micron regime. We go through depth filtration at 0.6 microns and then a 0.45 sterile membrane. That works pretty well. There was some suggestion that we run it through UV lights and all those sort of things because of the nature of the product. We don’t do that but we do take the extra precaution of running it through a 0.2 micron sterile filter now. We do that mainly because we don’t want to make any other additions like Velcorin — we just don’t add that kind of stuff to any of our products out of principle mainly.”
While avoiding going into specifics, Catlin unsurprisingly confirms that additives are made to Sidewood’s 0% products to help with mouthfeel.
“If you don’t add them, you’ve got a product that is sour and thin and horrible — it’s not a very nice product. And we do that in balance with added residual sugar or concentrate. We don’t want to create a product that’s lolly water. To reduce the amount of glucose and fructose you add you need to add other things, so it’s a real blending exercise.
“We’ve played around with them to get them right, there’s no doubt about it. Even now, with all the things we’ve been doing, going forward they will be even better. We’ve learned more since those initial releases,” Catlin admits, revealing another 0% product is also in the works that will “benefit from the learning curve that we’ve gone through”.