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APRIL ISSUE
Announcement:
Starting May 1st, our service lab will be available on a limited basis. Activity on campus is still minimal, and shipping and delivery are delayed, so arrangements need to be made in advance. We are only accepting samples upon request. For any questions please email mmoroney@iastate.edu.
Thank you for your cooperation!
How MGWII Staff is Keeping Busy while Social Distancing and Working from Home
Erin has continued making her delicious bread and baked goods while her daughter Naomi enjoys taste testing all of them!
Maureen- I’ve been cooking a lot, taking a lot of walks, and trying to be at least a little creative. For the first few days, I was doing a quick daily sketch of stuff related to wine and/or the lab – some turned out better than others – and I played along with the Getty Museum Challenge
(https://www.washingtonpost.com/travel/2020/04/03/people-are-re-creating-famous-artworks-with-their-pets-whatever-else-is-lying-around/).
I filled out my Census and sent in my absentee ballot request form for the primary on June 2, because who knows what the stay-home situation will be by then. (Story County residents can find a postage-paid form here: https://www.storycountyiowa.gov/DocumentCenter/View/265)
I tried making bread with (expired) wine yeast, which was a very moderate success.
I also contributed a piece to “The Pandemic Issue” of Backchannels Journal (https://www.backchannelsjournal.net/instant-publishing-the-pandemic-issue).
Jennie- Our extra time at home has included my best efforts at homeschooling a first grader and preschooler (which has me feeling super thankful for our teachers), chalk art, bike rides and walks, cattle chores, some landscaping, and running after farmers (big and small :D).
Sarahi- I was staying in Des Moines with my parents for several weeks, while I was there we started and havent finished a 2,000 piece puzzle, I dressed my dogs in old Halloween costumes, and I went to a couple of prenatal appointments. Now I'm back in Ames and enjoying the nice weather (still with my dogs)!
Somchai-  All of my running races have been cancelled or postponed so I’ve been hitting the trails on my own. We celebrated the Asian new year. I 3D printed a wine bottle holder an made some masks.
Sensory Tasting in The Winery
Erin Norton
 
Part 1: When to use a sensory test in your winery.

In this series of articles, Erin Norton (Education & Outreach Coordinator) will provide details on how you can use sensory evaluation in your winery.  Any questions or comments, please direct them to Erin at elnorton@iastate.edu.

Many of you have attended the MGWII’s Intensive Tasting Proficiency Training workshop that we have performed close to a dozen times.  During this workshop we try to teach you how to taste wine professionally, how to focus in on some of your senses while tasting wine (aroma, flavor, mouthfeel), how to identify some wine faults and how to describe what you are tasting.  We also briefly introduce the idea of sensory testing and how we at the institute use sensory evaluation in our research to understand new varieties, winemaking techniques and troubleshooting wine problems for you in our analytical lab.
You too can use some of these sensory evaluation tests in your own winery to gather information on your wines.  Instead of basing decisions on gut feelings, or customer anecdotes, sensory evaluation tests can help you add some numerical assurance to your decisions.

In this first article of a three part series, I will highlight some cases where you can use sensory evaluation to help your decision-making in the winery.  And it does not have to stop with winemaking decisions.  You can use some of these tests to evaluate the aesthetics of your labels, or marketing campaigns, or even develop a more in-depth research trial to detect if vineyard practices make a different on wine quality (feel free to contact Erin or others at the MGWII if you would like to chat about setting up a vineyard research trial).

It is always a good idea to get multiple opinions or interpretations of results you obtain in the winery.
 

Some situations where you could set up a sensory evaluation test include (but are not limited to):
  • Yeast Trials
    • If you want to evaluate how a particular yeast performs, and what sensory characteristics it imparts to the wine, do a small fermentation with the new yeast. (Be sure to process the grapes, and perform all winemaking identical between the regular yeast batch and the new yeast batch)
  • Fining Trials
    • Using the same batch of wine, try different fining products.Instead of just evaluating yourself, get others to help decide which wine is “better” or aligns with the style you are trying to make.
  • Back-label descriptions
Collect data from customers on what they smell or taste in a wine, and what they would pair it with.  Often times back-label descriptions are esoteric and do not connect with the target consumers.
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Microbial Terroir
Maureen Moroney
Recent Research on Microbial Terroir

Like much of the wine world, I’ve been thinking, reading, and talking a lot lately about the idea of microbial terroir in wine. That is, whether and how regional distributions of microbes like yeast and bacteria on grapes and in wine contribute to regionally-distinctive sensory expressions.
 
I was scheduled to give a talk on the topic at the end of March, but as you all know, the university cancelled all in-person events before that happened. So I recorded it instead.
 
It got a little long – I guess that’s what happens when it’s just me talking at my laptop in my kitchen, trying to describe sensory exercises without being able to do them in person – but you can find it on our Facebook page here (and feel free to skip through to the bits that interest you most): https://tinyurl.com/Microbial-Terroir-MGWII
Two of the articles I mentioned in the talk are below, and if this is a topic you’d like to explore, I highly recommend them.

The first is a research study correlating microbes, metabolites (like acids, esters, and lactones), and fermentation behavior by region. The figures may look a little intimidating at first, but the text is well-written and insightful.
 
Bokulich et al., 2016.
“Associations among Wine Grape Microbiome, Metabolome, and Fermentation Behavior Suggest Microbial Contribution to Regional Wine Characteristics.”
https://mbio.asm.org/content/7/3/e00631-16.full (Open Access)

Some excerpts:
“Traditional winemaking practices encourage or rely entirely on ‘native’ (noninoculated) microbiota to conduct fermentations, a practice that adherents regard as enhancing regional typicity. In spite of the well-defined role microbial interactions play in grapevine health, fruit quality, and wine quality, the influence of grape microbiota on regional characteristics of wines is undefined.”
 
“Many of these compounds represent acids, esters, and aldehydes, some of which are likely microbial. Others, such as tartaric acid, are strictly grape derived. Many of the grape-derived compounds, such as the phenolic compounds coumaric acid, gallic acid, catechin, epicatechin, and caffeic acid, are modified by microbial metabolism during wine fermentation.”
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Winery Process Water
Jennie Savits

Water is an important topic in the world of wine. Protecting and conserving resources is of utmost concern so water is often looked at from the standpoint of usage and treatment of wastewater. Water quality is also critically important in food and beverage production. The conditions of the water must be suitable for the purpose it serves.

Throughout the winemaking process, water serves many functions; it’s used as a tool, to clean and sanitize, and as an additive or processing aid to make/prepare additions. Clean, potable water for use in wine production is typically sourced from a municipal (tap), a rural water district, or a well. However, there are some considerations beyond drinking water standards (set by the EPA) when it comes it’s use for winemaking. In production settings, the term process water defines water used for a variety of functions; rinsing, cooling, product water, or transport. Process water is generally treated in some manner to best fit the application. In winemaking, both water hardness and chlorination need consideration.

Water Hardness
Water contains minerals (specifically calcium and magnesium) along with other alkali metals that lead to water hardness (Table 1). At a level over 120 mg/L measured as calcium carbonate, a given water source is considered hard. Hardness in water can cause issues with respect to cleaning and sanitation because it reduces the effectiveness of detergents (especially bicarbonates). Hardness also causes scale or deposits on equipment and can be a culprit in premature filter clogging.
Water hardness is especially problematic in conditions that are alkaline (pH >7) and/or increased temperature. These deposits are unsightly and lead to other organic debris build up that make cleaning more difficult. High mineral content in water can also decrease the effectiveness of ozone.

To combat the issue of water hardness, water testing and subsequent use of water softening or conditioning systems can be employed. Water from different sources will have different composition, so testing prior to implementing a treatment system is imperative to ensure the best results. Water softening systems typically utilize ion exchange to remove positively charged calcium and magnesium from the water by use of an ion exchange resin that exchanges the calcium and magnesium ions in the water with the positively charged sodium ions on the resin. This results in an increase of the salinity of the water. As an alternative to sodium, potassium resin can be used. This results in an increase of the potassium content of the water.
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Let's focus on.. with Dr. Watrelot
Focusing on Research Winemaking
Tannins in Grapes
 
In wine, polyphenols are responsible for the difference between white and red wines as they play a major role in the color and the texture/taste. Polyphenols are a large family of complex compounds including two groups, phenolic acids and flavonoids, recognized as having antioxidant and anti-inflammatory properties. Among this latter group, anthocyanins are responsible for the red-purple grape skins, sometimes flesh, color and condensed tannins are popular for their antioxidant properties and the astringency perception.

In this research winemaking focus, tannins in grapes will be explained starting from the chemical structure of tannins to the role of grape tannins in wine.

What are Grape tannins?
Grape tannins are also called condensed tannins or proanthocyanidins based upon their chemical structure. Condensed tannins are oligomers or polymers of flavan-3-ols that are a sub-group of flavonoid. As a result of acid hydrolysis in presence of alcohol at high temperature, proanthocyanidin releases an anthocyanidin by breaking the interflavan bonds (Figure 1). Tannins are highly reactive with proteins such as collagen from animal skins that has been discovered during the fabrication of leather. This physico-chemical property is involved in the astringency perception of red wine.
Figure 1. Condensed tannins or proanthocyanidins releasing anthocyanidins after an acid treatment with alcohol and high temperature. On the left, the molecule of tannin is composed of epicatechin, epigallocatechin, catechin and epicatechin (from top to bottom), and it releases different anthocyanidins (on the right).

Figure 1. Condensed tannins or proanthocyanidins releasing anthocyanidins after an acid treatment with alcohol and high temperature. On the left, the molecule of tannin is composed of epicatechin, epigallocatechin, catechin and epicatechin (from top to bottom), and it releases different anthocyanidins (on the right).

Grape condensed tannins are characterized by their four main constitutive units: epicatechin, catechin, epigallocatechin and epicatechin gallate which can be found as extension and/or in terminal units (Figure 1). The mean degree of polymerization (mDP) corresponds to the number of constitutive units which are linked to each other mostly through C4-C8 interflavan bonds. Those three characteristics of condensed tannins affect their conformation in red wine and also their interaction with other macromolecules. For example, galloyl groups or a high mDP are associated with high astringency intensity.
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Focusing on a Grape Variety
Petite Pearl
Petite Pearl is a cross between MN 1094 and E.S. 4-7-26 with Vitis species such as V. vinifera, V. riparia and V. labrusca among others. Tom Plocher in Hugo, Minnesota bred Petite Pearl in 1996 and the release of it was in 2010. Petite Pearl can resist to temperatures as low as -32°F. This cold-hardy grape variety is highly resistant to powdery and downy mildew and to black and bunch rot. Based on a report from the Northern grape project (Gomez et al., 2016), Petite Pearl does not seem to be susceptible or injured by copper-fungicide and sulfur-fungicide when applied in Wisconsin.

Bud break is late spring and it is a late-ripening variety with a range of GDD between 1350 to 1500 C (Plocher & Vines). The grape berries of Petite Pearl are black, weighing 2 g, compact and the clusters are very dense.

In a recent study, Scharfetter et al. (2019) measured the effect of leaf removal on polyphenols of cold-hardy grape varieties including Petite Pearl. The vines were planted in 2011 and were trained to a high cordon system. The harvest times varied from October 2nd in 2015 to September 12th in 2016. The yield was between 11.7 to 6.2 kg/vine at the respective harvest dates and the Ravaz index was 13.7 and 5.0 kg fruit/kg pruning, respectively.

In 2017 one-week postfermentation wine, the °Brix was 7.3, the TA was 7.77 g/L tartaric acid equivalent and the pH was at 3.62. The total phenolic concentration measured by a modified Folin-Ciocalteu method, was 1439 mg/L gallic equivalent in the control and significantly higher in wine made from leaf-removal treatment grapes. The concentration of monomeric anthocyanins and polymeric pigments were significantly higher in wine made from leaf-removal treatment grapes.
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