Get rid of the sour taste

[chaosmaster]

I am new here. We have a microbrewery in Nanjing, China. So, hello to everyone from China.

Recently we have brewed couple batches of hefeweizen using Chinese wheat, and the W3068 yeast, the first batch was very impressive, smooth taste and strong banana flavor. I was happy.

Now the problem is that, the second batch tastes sour.

Our wort boiling tun holds only 1T volume but our fermentation tank is 2t, so we have to make two seperated batches of wort in two days to fill up the ferm tank. Yeast was added only once to the first half.

During the making of the second batch. The first half went in well, CO2 came with characteristic banana fregrance. We were out of hops so we waited two days for the the second half. It went in well again, smelled fine for the first week, then we sealed the tank and let the pressure build up to 0.10 MPa.

Two weeks later, I tasted the beer, it was a little too sour. Not enough banana fragrance compared to our previouse production. I opened the pressure valve and let go the CO2 pressure. The gas smelled rubbery. Then I aerated the tank with CO2 for about 10 minutes, attempted to get rid of some of the bad smell, and finally pressurized the ferm tank to 0.15 MPa. I also lowered the temp to 5 C, (about 40F), during the next 10 days, I cropped the yeast every day. And I tasted it again...two days ago, it was still sour, with very mild banana flavor.

Questions are:
1. What have I done wrong? Do I seal the valve too early?
2. One major inccident was that the second half almost over-filled the ferm tank, spillage (with burps) came out from the side venting pipeline during the first three days. Could this affect the taste.
3. How to get rid of the sour taste. Flushing the wort with CO2 work effectively?

Thank you all.

[beerking1]

You have described two different off-flavors/aromas: sour, and rubbery.

Sour is likely from some bacterial or wild yeast contamination. Can you describe the sour flavor? Is it like vinegar, or like sour milk? Vinegar character is likely from acetobacter. Sour milk character is likely from lactobacillus. The most likely time this may have been introduced is during transfer of the yeast from one batch to the next. How did you transfer it? The safest method is cone to cone transfer. Dump the bottom sediment in your conical until it turns from brown to light tan/cream color. Shut off the valve, and change hoses, Make sure the hoses you hook up are as sanitary as you can possibly get them.
Now connect a hose from the primary to your next fermenter (empty). Make sure you have a sight glass inline so you can observe the yeast during transfer. Open that valve one the empty (sanitary) conical first, then open the valve on the (full) primary from your last batch. Watch the sight glass and close the valve when yeast slurry becomes beer. Now transfer your cooled wort onto the yeast in the empty fermenter.
With proper sanitation, you can dump the clean yeast into a sanitary bucket and put a lid on it and keep in it the cooler for a day or so.

This gets to your second off aroma: rubbery. This is likely from yeast autolysis. Basically, your yeasts have gone cannibal and begun consuming the dead cells in the culture. Hefe yeast is extremely fragile and short lived. So much so that i understand most German breweries that bottle condition use a lager yeast in the bottle for their Heffeweizens. I do not brew much heffe, but I have been told be many that this yeast will not last more than a day or two between batches unless you take extra measures to keep it viable.

Unfortunately, I don't think there is any way to remove these off characters from the beer you have, you just have to learn an move on.

[lhall]

Waiting two days for the second batch is a problem. You are introducing fresh wort (aerated?) into a fermentation that is probably almost done. You should ideally do both batches in the same day.

Also, our hefe yeast is very tempermental regarding pitching rate. Overpitching it reduces the nice bannana esters. If we under pitch it, the degree of fermentation is reduced. It would be very hard to control pitching rates with a cone-to-cone transfer.

[beerking1]

It would be very hard to control pitching rates with a cone-to-cone transfer.

Good point!

[chaosmaster]

Thank you all for your advise and help.

The sour taste is like sour apple, which i thought it would eventually go away. my major concern is the rubbery taste and lacking of fruity smell/taste. Overpitched? underpitched?

I did the cone to cone yeast transfer, just as you said. the first half was good which means the yeast was not contaminated. Autolysis? I doubt it because we cropped the yeast sediment from the third day, once every two days. the sediment has a white creamy color, just like other yeast dumps. However, it doesn't smell banana as other hefe yeast wastes.

well, it seems like there is nothing i can do but to wait and hope the beer will improve itself as time goes by. It is painful, but i will keep you all posted.

Thank you again.

[beerking1]

Sour apple or green apple aroma and flavor sounds like Acetaldehyde.

Acetaldehyde is naturally produced by the yeast in the early stages of fermentation, but is normally reduced to ethanol by yeast during the secondary fermentation. Higher levels in the finished beer can either mean the beer was moved off the yeast too soon, or possibly the finished beer was oxidized, converting ethanol back to acetaldehyde.

Some bacterial contamination can also produce Acetaldehyde, most notably Zymomonas or Acetobacter.

[gitchegumee]

Doesn't acetobacter require O2 to synthesize vinegar? With no O2 source (excess air movement over open fermenters), I've never seen an acetobacter infection. Are there other metabolic pathways to vinegar?

[fatty_matty]

Have you taken pH readings throughout the brew and fermentation process?

Checking pH is a fundamental and easy way to assertain that the quality of your wort and fermenting beer is in good shape. Is its below 3.88 then you could have some trouble on your hands and no amount of CO2 purging will make any difference im afraid.

We've lost a batch of weizen due to sourness, primarily because of lactobacillus. I remember the aroma was very unpleasant and sharp, the taste verged on that of cider.

You also mention that you were out of hops, did you only add hops to your second batch of wort? Personally I would never pitch yeast into unhopped wort it could lead to infection problems...

[chaosmaster]

To Fatty: the hop content is 0.37 kg per 1000L. (roughly 0.37oz per 5 gallon) we used Hallatau Hersbruck. I have brewed one batch of hefe with 0.5kg per 1000L, it worked fine.

pH value was checked only for the wort, but not though days during fermentation. I will take a pH reading and post it here.

[Jephro]

I use the 3068 too, we only use for 3 gens because of a slew of problems we have had in higher gens. One problem that took a while for me to get a handle on was sulfur production. I changed pitch rates, oxygenation, bunging, not bunging, temp, and finally figured out common denominator. Every time i filled up the FV and left little head space i got excess sulfur that had to be scrubbed out - sometimes successfully. Some or my best hefe's have been a single batch in a double tank.

I must strongly agree that YES, pitching rates on the 3068 play a huge role in the ester (banana) production. I also have found using a high oxygenation rate when underpitching seems to produce a better hefe. I like to stress the yeast not starve it.

[jason.koehler]

'Rubbery' describes phenols above flavor thresholds to me. I second the pH checks, especially during sparging.

I've also heard some stories before about breweries who make single batches great, but then run into infection problems with double batches. The tops of fermenters can be difficult to clean, and if you're overfilling it, you might be putting the wort into contact with some critters living on the top of the fermenter. On a single brew, not enough of them get into the mix to make a difference...but on a double...

[chaosmaster]

Jason, good thinking, how come I have never thought about that... the top corners of the fermentation tank.

It is only the second gen so I don't think the viability is an issue, however, I did overlooked the pitching rate for the second batch! We did a cone to cone yeast transfer and lost yeast counts that way. The first batch was good because we cultured the yeast in lab and pitched with the exact quantity.

Great feedbacks!

[chaosmaster]

Well, the sour taste is gone! after 15 days of cold storage at 35F (3C). Still the banana flavor is not as strong as the first batch.

Nevertheless, this once again proves that beer doesn't go bad easily. Viva la yeast!

[SRB]

So can it be deduced that this was not contamination but a yeast based issue?