I crushed and pressed my own pears this year hoping to make a perry. The original specific gravity (SG) was only 1.034 so I added 5 pounds (2.3 kg) of sugar, some British ale yeast and yeast energizer. It fermented for a bit, then stopped at about 1.025 and tastes very sweet. I then added a white wine yeast, but it still did not ferment. I also made a batch with both apples and pears and added 5 pounds (2.3 kg) of sugar. Like the perry, it fermented then stopped short and is sweet. I suspect the pears have non-fermentable sugars. Is there anything I can do to encourage further fermentation, or should I learn to enjoy sweet wines? One more note, we made a batch of perry from the same pear tree two years ago and it was delicious and dry. We let those pears soften much longer than the ones we used this year. Did allowing the pears to become very soft prior to pressing change the sugars to become more fermentable?
Kevin Buck
Via email

You are making me thirsty! I am a huge fan of cider and perry (pear cider), especially when it's tart, dry-ish and has a sparkling finish. Yummy yum yum! I applaud you for keeping this ancient and tasty art alive in your neck of the woods.
   
You present an interesting scenario above. Since I don't know your batch sizes (volume) I can't help you calculate what 5 pounds (2.3 kg) of dry sugar (cane sugar? Malt sugar?) would do to your specific gravity, though an initial specific gravity of 1.034, being about
8.5 °Brix, certainly needs some sugar added to it. It's possible you added too much, which would account for your stuck fermentation of about 6.5 °Brix or so (the 1.025 that you mention above). Once alcohol levels get above 14.5%, most yeasts start to struggle to complete a fermentation, which is why I try to never start my fermentations above 25.0 °Brix (1.106 specific gravity) if I can help it. Though the number varies from year to year and winery to winery, in my experience, alcohol conversion rates tend to be 0.55–0.58 alcohol points for every degree of Brix you start with. I recommend making sure you don't add too much sugar; be sure to measure your initial starting Brix and add sugar gradually to your must to avoid over doing it.
   
I'm no pomologist (fruit scientist), but from what I understand, letting pears soften (i.e. get ripe) prior to pressing doesn't make the sugars more fermentable per se, it just makes more sugar.  Soft, ripe fruit has a higher sugar concentration than hard, unripe fruit due to ethelyne gas triggering enzymatic activity, which transforms starches into sugars. My guess is that you experienced something this year that lead to both the stuck fermentations you witnessed.        
   
Though the causes of stuck fermentations are sometimes difficult to deduce (I myself was stumped by one of my own this year — arrrgh!), here are some possibilities:  you added too much sugar to your batches (and 5 lbs/2.23 kg of sugar could go a long way depending on your batch size), you had a bad batch of yeast that wasn't robust enough to finish the fermentation, you had an organism get into your fermentations (either acetobacter or pediococcus) that caused the VA to climb and the yeast to give up, or you didn't have enough of a certain kind of micronutrient.
   
The latter reason is particularly interesting because fermentations conducted with high levels of dry sugar (beet, cane, etc) often don't have the required nutrients or healthy fermentation factors your average yeast beastie requires. Perhaps the year you started with riper fruit, your yeast enjoyed the goodies (amino acids, pantothenate, biotin, vitamins, nitrogen, not to mention suspended solids/pulp that are often important for fermentation kinetics) that come with fermenting real fruit juice rather than a white sugar solution. Pure sugar adds degrees Brix to a fermentation (higher potential alcohol), but little else.


I can't remember anyone speaking to the use of ammonia as a cleaning agent in the winery. We use it for glass and plastic gear, and do not use it for metal. With it, I believe that it totally dissipates, and there is no possibility of a residue. Is it ok to use in the winery?
 PHIL FEINER
SAN CARLOS, CALIFORNIA

Regarding ammonia (chemical formula NH3), I’m glad you brought the subject up. There’s a reason why we don’t use ammonia for sanitation in the winery and one acronym says it all: DAP. More on that in just a little bit, however.        

Myself, I keep a little ammonia squirt bottle under the kitchen sink to remove persistent grease stains from my stovetop. Just squirt it on, wait a few seconds and wipe clean with my little scrubby sponge. Presto change-o, no more grease-o! I Love it for the occasional dirty-job use in kitchen, but not for my winery. Why, you ask? Let me explain.
   
One of the most popular and widely-used yeast nutrients for home and large-scale winemakers alike is DAP, aka: diammonium phosphate (chemical formula (NH4)2HPO4). When added to juice or must, the ammonia part of DAP disassociates (becomes free in solution) and is available to the fermentation as a source of nitrogen for your soon-to-be happy yeast beasties. Nitrogen (N) is a critical component for yeast metabolism and for the completion of a healthy fermentation. Grape juice and must naturally contain nitrogen, but often, if it is lacking, we supplement with other nitrogen-containing yeast nutrient blends, which are specially formulated for winemaking. Perhaps the cheapest sources of nitrogen is the aforementioned diammonium phosphate, usually sold in powder form. Feeding the right amount is important too; if you have residual nitrogen in your wine after it goes dry, you will just be feeding the leftovers to spoilage microbes. This is why, if you can afford it, it’s key to measure the “yeast assimilable nitrogen” (YAN) of your juice or must before adjusting. If you have a wine lab nearby and don’t mind paying for the privilege (depending on the lab, $35–75), get your baseline YAN (can range anywhere from about 50 to 300) and then only add nitrogen so that the initial total is about 300 ppm. This is enough to get a healthy fermentation but not too much so that you’ll have beaucoup leftover. As an aside, more-complex nutrient blends containing critical amino acids like argenine and proline as well as other yeast-supporting ingredients like yeast hulls are probably a better choice than DAP alone as they provide more balanced yeast nutrition.
   
So what does this all mean for your idea about using ammonia in the cellar to clean equipment? Well, if you’re rinsing ammonia (which contains lots of nitrogen) down the drain in your winery, it means you’ll be feeding the microbes (bacteria, fungi, yeast etc) that live in your drains, on your floors, and even in the nooks and crannies in your equipment (like underneath the lip of your plastic buckets, for instance, where fresh rinse water sometimes doesn’t quite go).        
   
I don’t know about you, but I like to keep the population of “bad guys” to a minimum in my winery, not add to it. In winemaking, when everything depends on a healthy fermentation during harvest, and then protection from undesirable microbes the rest of the year, it pays to have as clean of a cellar as possible with a minimal microbial population. Targeted ammonia application, when you do it at all, should be done to juice or must only. Otherwise you are not just feeding the yeast, you could also be feeding a beast!