Using leftover wort to prime next beer
TroubleShooting
Ken Durigan • Hainesville, Illinois asks,
I have been an all-grain brewer for the past two years. In the bottom of my boiling kettle, I always find a fair amount of hop trub mixed with wort, which I separate from the main primary. Just for grins, I dumped all but the thickest of this “mud” into a sanitized half-gallon growler and loosely put on the cap. By the next day, all of the trub had settled to the bottom of the growler and there was about a quart of clean wort on top. I siphoned this into sanitized bottles, then placed the bottles in 180° F water and held it there for 20 minutes. I then capped the bottles, let them cool and stuck them in the fridge. The sterile wort has a gravity of 1.113. I would like to use this wort to prime my latest batch of barleywine, but I don’t know how much to use. I don’t want bottle bombs, nor do I want undercarbonated brew. How much should I add in a 4.5-gallon batch to give the proper carbonation level? The specific gravity of the barleywine is 1.018, if that makes a difference. Also, is there any reason to not use the “nasties” from the boiling kettle in the way I have described? I have done this for the past few batches, so I now have a growing supply of this wort for yeast starters and for the occasional bottling that I do.
Priming with wort is very tricky, because wort is not completely fermentable and its fermentability varies from batch to batch. Breweries that bottle-condition with wort determine the fermentability of each lot before use and have tables that enable them to consistently carbonate with it.
If you want your barleywine to be its best and want to carbonate with wort, add one liter of the high-gravity wort to the beer, condition it in a keg, and carefully bleed off the excess pressure to fine-tune the carbonation level. If you try to bottle it using wort, the results very likely will be disappointing unless you do some trial runs to determine the right amount to add. By using a series of voodoo calculations, I estimate that there is about 190 grams of fermentable sugar in one liter of your 1.113 SG wort. These 190 grams of sugar will produce about 95 grams of carbon dioxide. A good carbonation level is five grams of carbon dioxide per liter of beer; therefore, to carbonate 4.5 gallons of beer you will need 900 ml (30 ounces) of your 1.113 SG wort. This sounds convincing, but I don’t have much faith in bottle conditioning unless I run some trials. So condition it in a keg or use plain old corn sugar for the priming.
As far as using the “nasties,” it sounds like you are employing a clever method of squeezing out good wort from what most people discard as waste. I don’t agree with your method used to “sterilize” the wort, however. Cold wort from the refrigerator transferred to a bottle and submerged in an 180° F water bath for 20 minutes is not the same as heating the wort to 180° F (or higher) and holding for 20 minutes. Your method might not even heat the wort to 180° F after 20 minutes. I recommend putting the loosely capped bottles in boiling water for 30 minutes to ensure sterilization of the wort. Other than that, I think your method is very slick!
